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* possible deadlock in vfs_fallocate
@ 2018-04-29 17:00 syzbot
  2018-05-09  7:57 ` Eric Biggers
  0 siblings, 1 reply; 5+ messages in thread
From: syzbot @ 2018-04-29 17:00 UTC (permalink / raw)
  To: linux-fsdevel, linux-kernel, syzkaller-bugs, viro

Hello,

syzbot hit the following crash on upstream commit
cdface5209349930ae1b51338763c8e029971b97 (Sun Apr 29 03:07:21 2018 +0000)
Merge tag 'for_linus_stable' of  
git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=148c2885d71194f18d28

C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5054004375584768
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=6438048191479808
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5404215203594240
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=7043958930931867332
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+148c2885d71194f18d28@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.
If you forward the report, please keep this part and the footer.

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)

======================================================
WARNING: possible circular locking dependency detected
4.17.0-rc2+ #23 Not tainted
------------------------------------------------------
syz-executor715/4492 is trying to acquire lock:
         (ptrval) (sb_writers#6){.+.+}, at: file_start_write  
include/linux/fs.h:2718 [inline]
         (ptrval) (sb_writers#6){.+.+}, at: vfs_fallocate+0x5be/0x8d0  
fs/open.c:318

but task is already holding lock:
         (ptrval) (ashmem_mutex){+.+.}, at: ashmem_shrink_scan+0xac/0x560  
drivers/staging/android/ashmem.c:440

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (ashmem_mutex){+.+.}:
        __mutex_lock_common kernel/locking/mutex.c:756 [inline]
        __mutex_lock+0x16d/0x17f0 kernel/locking/mutex.c:893
        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
        ashmem_mmap+0x53/0x460 drivers/staging/android/ashmem.c:361
        call_mmap include/linux/fs.h:1789 [inline]
        mmap_region+0xd13/0x1820 mm/mmap.c:1723
        do_mmap+0xc79/0x11d0 mm/mmap.c:1494
        do_mmap_pgoff include/linux/mm.h:2237 [inline]
        vm_mmap_pgoff+0x1fb/0x2a0 mm/util.c:357
        ksys_mmap_pgoff+0x4c9/0x640 mm/mmap.c:1544
        __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
        __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
        __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (&mm->mmap_sem){++++}:
        __might_fault+0x155/0x1e0 mm/memory.c:4555
        _copy_to_user+0x30/0x110 lib/usercopy.c:25
        copy_to_user include/linux/uaccess.h:155 [inline]
        filldir+0x1ea/0x3a0 fs/readdir.c:196
        dir_emit_dot include/linux/fs.h:3378 [inline]
        dir_emit_dots include/linux/fs.h:3389 [inline]
        dcache_readdir+0x13a/0x620 fs/libfs.c:192
        iterate_dir+0x4b0/0x5d0 fs/readdir.c:51
        __do_sys_getdents fs/readdir.c:231 [inline]
        __se_sys_getdents fs/readdir.c:212 [inline]
        __x64_sys_getdents+0x293/0x4e0 fs/readdir.c:212
        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&sb->s_type->i_mutex_key#11){++++}:
        down_write+0x87/0x120 kernel/locking/rwsem.c:70
        inode_lock include/linux/fs.h:713 [inline]
        do_last fs/namei.c:3274 [inline]
        path_openat+0x123b/0x4e20 fs/namei.c:3501
        do_filp_open+0x249/0x350 fs/namei.c:3535
        do_sys_open+0x56f/0x740 fs/open.c:1093
        __do_sys_open fs/open.c:1111 [inline]
        __se_sys_open fs/open.c:1106 [inline]
        __x64_sys_open+0x7e/0xc0 fs/open.c:1106
        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (sb_writers#6){.+.+}:
        lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
        percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36  
[inline]
        percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
        __sb_start_write+0x1e9/0x300 fs/super.c:1385
        file_start_write include/linux/fs.h:2718 [inline]
        vfs_fallocate+0x5be/0x8d0 fs/open.c:318
        ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
        ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
        vfs_ioctl fs/ioctl.c:46 [inline]
        file_ioctl fs/ioctl.c:500 [inline]
        do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
        ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
        __do_sys_ioctl fs/ioctl.c:708 [inline]
        __se_sys_ioctl fs/ioctl.c:706 [inline]
        __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
        entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
   sb_writers#6 --> &mm->mmap_sem --> ashmem_mutex

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(ashmem_mutex);
                                lock(&mm->mmap_sem);
                                lock(ashmem_mutex);
   lock(sb_writers#6);

  *** DEADLOCK ***

1 lock held by syz-executor715/4492:
  #0:         (ptrval) (ashmem_mutex){+.+.}, at:  
ashmem_shrink_scan+0xac/0x560 drivers/staging/android/ashmem.c:440

stack backtrace:
CPU: 1 PID: 4492 Comm: syz-executor715 Not tainted 4.17.0-rc2+ #23
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
  print_circular_bug.isra.36.cold.54+0x1bd/0x27d  
kernel/locking/lockdep.c:1223
  check_prev_add kernel/locking/lockdep.c:1863 [inline]
  check_prevs_add kernel/locking/lockdep.c:1976 [inline]
  validate_chain kernel/locking/lockdep.c:2417 [inline]
  __lock_acquire+0x343e/0x5140 kernel/locking/lockdep.c:3431
  lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
  percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline]
  percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
  __sb_start_write+0x1e9/0x300 fs/super.c:1385
  file_start_write include/linux/fs.h:2718 [inline]
  vfs_fallocate+0x5be/0x8d0 fs/open.c:318
  ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
  ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
  vfs_ioctl fs/ioctl.c:46 [inline]
  file_ioctl fs/ioctl.c:500 [inline]
  do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
  __do_sys_ioctl fs/ioctl.c:708 [inline]
  __se_sys_ioctl fs/ioctl.c:706 [inline]
  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440179
RSP: 002b:00007ffc165d4a28 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 6873612f7665642f RCX: 0000000000440179
RDX: 0000000000000000 RSI: 000000000000770a RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000004 R11: 0000000000000217 R12: 00000000004016a0
R13: 0000000000401730 R14: 0000000000000000 R15: 0000000000000000
random: crng init done


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzkaller@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is  
merged
into any tree, please reply to this email with:
#syz fix: exact-commit-title
If you want to test a patch for this bug, please reply with:
#syz test: git://repo/address.git branch
and provide the patch inline or as an attachment.
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug  
report.
Note: all commands must start from beginning of the line in the email body.

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: possible deadlock in vfs_fallocate
  2018-04-29 17:00 possible deadlock in vfs_fallocate syzbot
@ 2018-05-09  7:57 ` Eric Biggers
  2018-05-09 16:56   ` Todd Kjos
  0 siblings, 1 reply; 5+ messages in thread
From: Eric Biggers @ 2018-05-09  7:57 UTC (permalink / raw)
  To: Greg Kroah-Hartman, Arve Hjønnevåg, Todd Kjos,
	Martijn Coenen, devel
  Cc: linux-fsdevel, linux-kernel, syzkaller-bugs, syzbot

[+ashmem maintainers]

On Sun, Apr 29, 2018 at 10:00:03AM -0700, syzbot wrote:
> Hello,
> 
> syzbot hit the following crash on upstream commit
> cdface5209349930ae1b51338763c8e029971b97 (Sun Apr 29 03:07:21 2018 +0000)
> Merge tag 'for_linus_stable' of
> git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=148c2885d71194f18d28
> 
> C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5054004375584768
> syzkaller reproducer:
> https://syzkaller.appspot.com/x/repro.syz?id=6438048191479808
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=5404215203594240
> Kernel config:
> https://syzkaller.appspot.com/x/.config?id=7043958930931867332
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+148c2885d71194f18d28@syzkaller.appspotmail.com
> It will help syzbot understand when the bug is fixed. See footer for
> details.
> If you forward the report, please keep this part and the footer.
> 
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.17.0-rc2+ #23 Not tainted
> ------------------------------------------------------
> syz-executor715/4492 is trying to acquire lock:
>         (ptrval) (sb_writers#6){.+.+}, at: file_start_write
> include/linux/fs.h:2718 [inline]
>         (ptrval) (sb_writers#6){.+.+}, at: vfs_fallocate+0x5be/0x8d0
> fs/open.c:318
> 
> but task is already holding lock:
>         (ptrval) (ashmem_mutex){+.+.}, at: ashmem_shrink_scan+0xac/0x560
> drivers/staging/android/ashmem.c:440
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #3 (ashmem_mutex){+.+.}:
>        __mutex_lock_common kernel/locking/mutex.c:756 [inline]
>        __mutex_lock+0x16d/0x17f0 kernel/locking/mutex.c:893
>        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>        ashmem_mmap+0x53/0x460 drivers/staging/android/ashmem.c:361
>        call_mmap include/linux/fs.h:1789 [inline]
>        mmap_region+0xd13/0x1820 mm/mmap.c:1723
>        do_mmap+0xc79/0x11d0 mm/mmap.c:1494
>        do_mmap_pgoff include/linux/mm.h:2237 [inline]
>        vm_mmap_pgoff+0x1fb/0x2a0 mm/util.c:357
>        ksys_mmap_pgoff+0x4c9/0x640 mm/mmap.c:1544
>        __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
>        __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
>        __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
>        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> -> #2 (&mm->mmap_sem){++++}:
>        __might_fault+0x155/0x1e0 mm/memory.c:4555
>        _copy_to_user+0x30/0x110 lib/usercopy.c:25
>        copy_to_user include/linux/uaccess.h:155 [inline]
>        filldir+0x1ea/0x3a0 fs/readdir.c:196
>        dir_emit_dot include/linux/fs.h:3378 [inline]
>        dir_emit_dots include/linux/fs.h:3389 [inline]
>        dcache_readdir+0x13a/0x620 fs/libfs.c:192
>        iterate_dir+0x4b0/0x5d0 fs/readdir.c:51
>        __do_sys_getdents fs/readdir.c:231 [inline]
>        __se_sys_getdents fs/readdir.c:212 [inline]
>        __x64_sys_getdents+0x293/0x4e0 fs/readdir.c:212
>        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> -> #1 (&sb->s_type->i_mutex_key#11){++++}:
>        down_write+0x87/0x120 kernel/locking/rwsem.c:70
>        inode_lock include/linux/fs.h:713 [inline]
>        do_last fs/namei.c:3274 [inline]
>        path_openat+0x123b/0x4e20 fs/namei.c:3501
>        do_filp_open+0x249/0x350 fs/namei.c:3535
>        do_sys_open+0x56f/0x740 fs/open.c:1093
>        __do_sys_open fs/open.c:1111 [inline]
>        __se_sys_open fs/open.c:1106 [inline]
>        __x64_sys_open+0x7e/0xc0 fs/open.c:1106
>        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> -> #0 (sb_writers#6){.+.+}:
>        lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
>        percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36
> [inline]
>        percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
>        __sb_start_write+0x1e9/0x300 fs/super.c:1385
>        file_start_write include/linux/fs.h:2718 [inline]
>        vfs_fallocate+0x5be/0x8d0 fs/open.c:318
>        ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
>        ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
>        vfs_ioctl fs/ioctl.c:46 [inline]
>        file_ioctl fs/ioctl.c:500 [inline]
>        do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
>        ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
>        __do_sys_ioctl fs/ioctl.c:708 [inline]
>        __se_sys_ioctl fs/ioctl.c:706 [inline]
>        __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
>        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> other info that might help us debug this:
> 
> Chain exists of:
>   sb_writers#6 --> &mm->mmap_sem --> ashmem_mutex
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(ashmem_mutex);
>                                lock(&mm->mmap_sem);
>                                lock(ashmem_mutex);
>   lock(sb_writers#6);
> 
>  *** DEADLOCK ***
> 
> 1 lock held by syz-executor715/4492:
>  #0:         (ptrval) (ashmem_mutex){+.+.}, at:
> ashmem_shrink_scan+0xac/0x560 drivers/staging/android/ashmem.c:440
> 
> stack backtrace:
> CPU: 1 PID: 4492 Comm: syz-executor715 Not tainted 4.17.0-rc2+ #23
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>  print_circular_bug.isra.36.cold.54+0x1bd/0x27d
> kernel/locking/lockdep.c:1223
>  check_prev_add kernel/locking/lockdep.c:1863 [inline]
>  check_prevs_add kernel/locking/lockdep.c:1976 [inline]
>  validate_chain kernel/locking/lockdep.c:2417 [inline]
>  __lock_acquire+0x343e/0x5140 kernel/locking/lockdep.c:3431
>  lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
>  percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline]
>  percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
>  __sb_start_write+0x1e9/0x300 fs/super.c:1385
>  file_start_write include/linux/fs.h:2718 [inline]
>  vfs_fallocate+0x5be/0x8d0 fs/open.c:318
>  ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
>  ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  file_ioctl fs/ioctl.c:500 [inline]
>  do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
>  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
>  __do_sys_ioctl fs/ioctl.c:708 [inline]
>  __se_sys_ioctl fs/ioctl.c:706 [inline]
>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x440179
> RSP: 002b:00007ffc165d4a28 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 6873612f7665642f RCX: 0000000000440179
> RDX: 0000000000000000 RSI: 000000000000770a RDI: 0000000000000004
> RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000004 R11: 0000000000000217 R12: 00000000004016a0
> R13: 0000000000401730 R14: 0000000000000000 R15: 0000000000000000
> random: crng init done
> 
> 
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@googlegroups.com.
> 
> syzbot will keep track of this bug report.
> If you forgot to add the Reported-by tag, once the fix for this bug is
> merged
> into any tree, please reply to this email with:
> #syz fix: exact-commit-title
> If you want to test a patch for this bug, please reply with:
> #syz test: git://repo/address.git branch
> and provide the patch inline or as an attachment.
> To mark this as a duplicate of another syzbot report, please reply with:
> #syz dup: exact-subject-of-another-report
> If it's a one-off invalid bug report, please reply with:
> #syz invalid
> Note: if the crash happens again, it will cause creation of a new bug
> report.
> Note: all commands must start from beginning of the line in the email body.

Looks like yet another locking bug in ashmem.  ashmem_mutex normally ranks below
mmap_sem, but ashmem_shrink_scan() inverts that order, via the
file_start_write() in vfs_fallocate().

- Eric

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: possible deadlock in vfs_fallocate
  2018-05-09  7:57 ` Eric Biggers
@ 2018-05-09 16:56   ` Todd Kjos
  2019-01-22 13:58     ` Dmitry Vyukov
  0 siblings, 1 reply; 5+ messages in thread
From: Todd Kjos @ 2018-05-09 16:56 UTC (permalink / raw)
  To: Eric Biggers, Joel Fernandes
  Cc: Greg Kroah-Hartman, Arve Hjønnevåg, Todd Kjos,
	Martijn Coenen, open list:ANDROID DRIVERS, linux-fsdevel, LKML,
	syzkaller-bugs, syzbot+148c2885d71194f18d28

[-- Attachment #1: Type: text/plain, Size: 9296 bytes --]

+Joel Fernandes <joelaf@google.com>

On Wed, May 9, 2018 at 12:55 AM Eric Biggers <ebiggers3@gmail.com> wrote:

> [+ashmem maintainers]
>
> On Sun, Apr 29, 2018 at 10:00:03AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot hit the following crash on upstream commit
> > cdface5209349930ae1b51338763c8e029971b97 (Sun Apr 29 03:07:21 2018 +0000)
> > Merge tag 'for_linus_stable' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
> > syzbot dashboard link:
> > https://syzkaller.appspot.com/bug?extid=148c2885d71194f18d28
> >
> > C reproducer:
> https://syzkaller.appspot.com/x/repro.c?id=5054004375584768
> > syzkaller reproducer:
> > https://syzkaller.appspot.com/x/repro.syz?id=6438048191479808
> > Raw console output:
> > https://syzkaller.appspot.com/x/log.txt?id=5404215203594240
> > Kernel config:
> > https://syzkaller.appspot.com/x/.config?id=7043958930931867332
> > compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the
> commit:
> > Reported-by: syzbot+148c2885d71194f18d28@syzkaller.appspotmail.com
> > It will help syzbot understand when the bug is fixed. See footer for
> > details.
> > If you forward the report, please keep this part and the footer.
> >
> > random: sshd: uninitialized urandom read (32 bytes read)
> > random: sshd: uninitialized urandom read (32 bytes read)
> > random: sshd: uninitialized urandom read (32 bytes read)
> >
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > 4.17.0-rc2+ #23 Not tainted
> > ------------------------------------------------------
> > syz-executor715/4492 is trying to acquire lock:
> >         (ptrval) (sb_writers#6){.+.+}, at: file_start_write
> > include/linux/fs.h:2718 [inline]
> >         (ptrval) (sb_writers#6){.+.+}, at: vfs_fallocate+0x5be/0x8d0
> > fs/open.c:318
> >
> > but task is already holding lock:
> >         (ptrval) (ashmem_mutex){+.+.}, at: ashmem_shrink_scan+0xac/0x560
> > drivers/staging/android/ashmem.c:440
> >
> > which lock already depends on the new lock.
> >
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #3 (ashmem_mutex){+.+.}:
> >        __mutex_lock_common kernel/locking/mutex.c:756 [inline]
> >        __mutex_lock+0x16d/0x17f0 kernel/locking/mutex.c:893
> >        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
> >        ashmem_mmap+0x53/0x460 drivers/staging/android/ashmem.c:361
> >        call_mmap include/linux/fs.h:1789 [inline]
> >        mmap_region+0xd13/0x1820 mm/mmap.c:1723
> >        do_mmap+0xc79/0x11d0 mm/mmap.c:1494
> >        do_mmap_pgoff include/linux/mm.h:2237 [inline]
> >        vm_mmap_pgoff+0x1fb/0x2a0 mm/util.c:357
> >        ksys_mmap_pgoff+0x4c9/0x640 mm/mmap.c:1544
> >        __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
> >        __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
> >        __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
> >        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
> >        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > -> #2 (&mm->mmap_sem){++++}:
> >        __might_fault+0x155/0x1e0 mm/memory.c:4555
> >        _copy_to_user+0x30/0x110 lib/usercopy.c:25
> >        copy_to_user include/linux/uaccess.h:155 [inline]
> >        filldir+0x1ea/0x3a0 fs/readdir.c:196
> >        dir_emit_dot include/linux/fs.h:3378 [inline]
> >        dir_emit_dots include/linux/fs.h:3389 [inline]
> >        dcache_readdir+0x13a/0x620 fs/libfs.c:192
> >        iterate_dir+0x4b0/0x5d0 fs/readdir.c:51
> >        __do_sys_getdents fs/readdir.c:231 [inline]
> >        __se_sys_getdents fs/readdir.c:212 [inline]
> >        __x64_sys_getdents+0x293/0x4e0 fs/readdir.c:212
> >        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
> >        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > -> #1 (&sb->s_type->i_mutex_key#11){++++}:
> >        down_write+0x87/0x120 kernel/locking/rwsem.c:70
> >        inode_lock include/linux/fs.h:713 [inline]
> >        do_last fs/namei.c:3274 [inline]
> >        path_openat+0x123b/0x4e20 fs/namei.c:3501
> >        do_filp_open+0x249/0x350 fs/namei.c:3535
> >        do_sys_open+0x56f/0x740 fs/open.c:1093
> >        __do_sys_open fs/open.c:1111 [inline]
> >        __se_sys_open fs/open.c:1106 [inline]
> >        __x64_sys_open+0x7e/0xc0 fs/open.c:1106
> >        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
> >        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > -> #0 (sb_writers#6){.+.+}:
> >        lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
> >        percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36
> > [inline]
> >        percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
> >        __sb_start_write+0x1e9/0x300 fs/super.c:1385
> >        file_start_write include/linux/fs.h:2718 [inline]
> >        vfs_fallocate+0x5be/0x8d0 fs/open.c:318
> >        ashmem_shrink_scan+0x1f1/0x560
> drivers/staging/android/ashmem.c:447
> >        ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
> >        vfs_ioctl fs/ioctl.c:46 [inline]
> >        file_ioctl fs/ioctl.c:500 [inline]
> >        do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
> >        ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
> >        __do_sys_ioctl fs/ioctl.c:708 [inline]
> >        __se_sys_ioctl fs/ioctl.c:706 [inline]
> >        __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
> >        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
> >        entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > other info that might help us debug this:
> >
> > Chain exists of:
> >   sb_writers#6 --> &mm->mmap_sem --> ashmem_mutex
> >
> >  Possible unsafe locking scenario:
> >
> >        CPU0                    CPU1
> >        ----                    ----
> >   lock(ashmem_mutex);
> >                                lock(&mm->mmap_sem);
> >                                lock(ashmem_mutex);
> >   lock(sb_writers#6);
> >
> >  *** DEADLOCK ***
> >
> > 1 lock held by syz-executor715/4492:
> >  #0:         (ptrval) (ashmem_mutex){+.+.}, at:
> > ashmem_shrink_scan+0xac/0x560 drivers/staging/android/ashmem.c:440
> >
> > stack backtrace:
> > CPU: 1 PID: 4492 Comm: syz-executor715 Not tainted 4.17.0-rc2+ #23
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Call Trace:
> >  __dump_stack lib/dump_stack.c:77 [inline]
> >  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
> >  print_circular_bug.isra.36.cold.54+0x1bd/0x27d
> > kernel/locking/lockdep.c:1223
> >  check_prev_add kernel/locking/lockdep.c:1863 [inline]
> >  check_prevs_add kernel/locking/lockdep.c:1976 [inline]
> >  validate_chain kernel/locking/lockdep.c:2417 [inline]
> >  __lock_acquire+0x343e/0x5140 kernel/locking/lockdep.c:3431
> >  lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
> >  percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36
> [inline]
> >  percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
> >  __sb_start_write+0x1e9/0x300 fs/super.c:1385
> >  file_start_write include/linux/fs.h:2718 [inline]
> >  vfs_fallocate+0x5be/0x8d0 fs/open.c:318
> >  ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
> >  ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
> >  vfs_ioctl fs/ioctl.c:46 [inline]
> >  file_ioctl fs/ioctl.c:500 [inline]
> >  do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
> >  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
> >  __do_sys_ioctl fs/ioctl.c:708 [inline]
> >  __se_sys_ioctl fs/ioctl.c:706 [inline]
> >  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
> >  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
> >  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x440179
> > RSP: 002b:00007ffc165d4a28 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 6873612f7665642f RCX: 0000000000440179
> > RDX: 0000000000000000 RSI: 000000000000770a RDI: 0000000000000004
> > RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000004 R11: 0000000000000217 R12: 00000000004016a0
> > R13: 0000000000401730 R14: 0000000000000000 R15: 0000000000000000
> > random: crng init done
> >
> >
> > ---
> > This bug is generated by a dumb bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for details.
> > Direct all questions to syzkaller@googlegroups.com.
> >
> > syzbot will keep track of this bug report.
> > If you forgot to add the Reported-by tag, once the fix for this bug is
> > merged
> > into any tree, please reply to this email with:
> > #syz fix: exact-commit-title
> > If you want to test a patch for this bug, please reply with:
> > #syz test: git://repo/address.git branch
> > and provide the patch inline or as an attachment.
> > To mark this as a duplicate of another syzbot report, please reply with:
> > #syz dup: exact-subject-of-another-report
> > If it's a one-off invalid bug report, please reply with:
> > #syz invalid
> > Note: if the crash happens again, it will cause creation of a new bug
> > report.
> > Note: all commands must start from beginning of the line in the email
> body.
>
> Looks like yet another locking bug in ashmem.  ashmem_mutex normally ranks
> below
> mmap_sem, but ashmem_shrink_scan() inverts that order, via the
> file_start_write() in vfs_fallocate().
>
> - Eric
>

[-- Attachment #2: Type: text/html, Size: 12083 bytes --]

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: possible deadlock in vfs_fallocate
  2018-05-09 16:56   ` Todd Kjos
@ 2019-01-22 13:58     ` Dmitry Vyukov
  2019-01-22 14:26       ` syzbot
  0 siblings, 1 reply; 5+ messages in thread
From: Dmitry Vyukov @ 2019-01-22 13:58 UTC (permalink / raw)
  To: Todd Kjos
  Cc: Eric Biggers, Joel Fernandes, Greg Kroah-Hartman,
	Arve Hjønnevåg, Todd Kjos, Martijn Coenen,
	open list:ANDROID DRIVERS, linux-fsdevel, LKML, syzkaller-bugs,
	syzbot+148c2885d71194f18d28, Tetsuo Handa

[-- Attachment #1: Type: text/plain, Size: 9684 bytes --]

On Wed, May 9, 2018 at 6:57 PM 'Todd Kjos' via syzkaller-bugs
<syzkaller-bugs@googlegroups.com> wrote:
>
> +Joel Fernandes
>
> On Wed, May 9, 2018 at 12:55 AM Eric Biggers <ebiggers3@gmail.com> wrote:
>>
>> [+ashmem maintainers]
>>
>> On Sun, Apr 29, 2018 at 10:00:03AM -0700, syzbot wrote:
>> > Hello,
>> >
>> > syzbot hit the following crash on upstream commit
>> > cdface5209349930ae1b51338763c8e029971b97 (Sun Apr 29 03:07:21 2018 +0000)
>> > Merge tag 'for_linus_stable' of
>> > git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
>> > syzbot dashboard link:
>> > https://syzkaller.appspot.com/bug?extid=148c2885d71194f18d28
>> >
>> > C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5054004375584768
>> > syzkaller reproducer:
>> > https://syzkaller.appspot.com/x/repro.syz?id=6438048191479808
>> > Raw console output:
>> > https://syzkaller.appspot.com/x/log.txt?id=5404215203594240
>> > Kernel config:
>> > https://syzkaller.appspot.com/x/.config?id=7043958930931867332
>> > compiler: gcc (GCC) 8.0.1 20180413 (experimental)

Let's test Tetsuo's patch

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master



>> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> > Reported-by: syzbot+148c2885d71194f18d28@syzkaller.appspotmail.com
>> > It will help syzbot understand when the bug is fixed. See footer for
>> > details.
>> > If you forward the report, please keep this part and the footer.
>> >
>> > random: sshd: uninitialized urandom read (32 bytes read)
>> > random: sshd: uninitialized urandom read (32 bytes read)
>> > random: sshd: uninitialized urandom read (32 bytes read)
>> >
>> > ======================================================
>> > WARNING: possible circular locking dependency detected
>> > 4.17.0-rc2+ #23 Not tainted
>> > ------------------------------------------------------
>> > syz-executor715/4492 is trying to acquire lock:
>> >         (ptrval) (sb_writers#6){.+.+}, at: file_start_write
>> > include/linux/fs.h:2718 [inline]
>> >         (ptrval) (sb_writers#6){.+.+}, at: vfs_fallocate+0x5be/0x8d0
>> > fs/open.c:318
>> >
>> > but task is already holding lock:
>> >         (ptrval) (ashmem_mutex){+.+.}, at: ashmem_shrink_scan+0xac/0x560
>> > drivers/staging/android/ashmem.c:440
>> >
>> > which lock already depends on the new lock.
>> >
>> >
>> > the existing dependency chain (in reverse order) is:
>> >
>> > -> #3 (ashmem_mutex){+.+.}:
>> >        __mutex_lock_common kernel/locking/mutex.c:756 [inline]
>> >        __mutex_lock+0x16d/0x17f0 kernel/locking/mutex.c:893
>> >        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>> >        ashmem_mmap+0x53/0x460 drivers/staging/android/ashmem.c:361
>> >        call_mmap include/linux/fs.h:1789 [inline]
>> >        mmap_region+0xd13/0x1820 mm/mmap.c:1723
>> >        do_mmap+0xc79/0x11d0 mm/mmap.c:1494
>> >        do_mmap_pgoff include/linux/mm.h:2237 [inline]
>> >        vm_mmap_pgoff+0x1fb/0x2a0 mm/util.c:357
>> >        ksys_mmap_pgoff+0x4c9/0x640 mm/mmap.c:1544
>> >        __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
>> >        __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
>> >        __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
>> >        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> >        entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > -> #2 (&mm->mmap_sem){++++}:
>> >        __might_fault+0x155/0x1e0 mm/memory.c:4555
>> >        _copy_to_user+0x30/0x110 lib/usercopy.c:25
>> >        copy_to_user include/linux/uaccess.h:155 [inline]
>> >        filldir+0x1ea/0x3a0 fs/readdir.c:196
>> >        dir_emit_dot include/linux/fs.h:3378 [inline]
>> >        dir_emit_dots include/linux/fs.h:3389 [inline]
>> >        dcache_readdir+0x13a/0x620 fs/libfs.c:192
>> >        iterate_dir+0x4b0/0x5d0 fs/readdir.c:51
>> >        __do_sys_getdents fs/readdir.c:231 [inline]
>> >        __se_sys_getdents fs/readdir.c:212 [inline]
>> >        __x64_sys_getdents+0x293/0x4e0 fs/readdir.c:212
>> >        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> >        entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > -> #1 (&sb->s_type->i_mutex_key#11){++++}:
>> >        down_write+0x87/0x120 kernel/locking/rwsem.c:70
>> >        inode_lock include/linux/fs.h:713 [inline]
>> >        do_last fs/namei.c:3274 [inline]
>> >        path_openat+0x123b/0x4e20 fs/namei.c:3501
>> >        do_filp_open+0x249/0x350 fs/namei.c:3535
>> >        do_sys_open+0x56f/0x740 fs/open.c:1093
>> >        __do_sys_open fs/open.c:1111 [inline]
>> >        __se_sys_open fs/open.c:1106 [inline]
>> >        __x64_sys_open+0x7e/0xc0 fs/open.c:1106
>> >        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> >        entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > -> #0 (sb_writers#6){.+.+}:
>> >        lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
>> >        percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36
>> > [inline]
>> >        percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
>> >        __sb_start_write+0x1e9/0x300 fs/super.c:1385
>> >        file_start_write include/linux/fs.h:2718 [inline]
>> >        vfs_fallocate+0x5be/0x8d0 fs/open.c:318
>> >        ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
>> >        ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
>> >        vfs_ioctl fs/ioctl.c:46 [inline]
>> >        file_ioctl fs/ioctl.c:500 [inline]
>> >        do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
>> >        ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
>> >        __do_sys_ioctl fs/ioctl.c:708 [inline]
>> >        __se_sys_ioctl fs/ioctl.c:706 [inline]
>> >        __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
>> >        do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> >        entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > other info that might help us debug this:
>> >
>> > Chain exists of:
>> >   sb_writers#6 --> &mm->mmap_sem --> ashmem_mutex
>> >
>> >  Possible unsafe locking scenario:
>> >
>> >        CPU0                    CPU1
>> >        ----                    ----
>> >   lock(ashmem_mutex);
>> >                                lock(&mm->mmap_sem);
>> >                                lock(ashmem_mutex);
>> >   lock(sb_writers#6);
>> >
>> >  *** DEADLOCK ***
>> >
>> > 1 lock held by syz-executor715/4492:
>> >  #0:         (ptrval) (ashmem_mutex){+.+.}, at:
>> > ashmem_shrink_scan+0xac/0x560 drivers/staging/android/ashmem.c:440
>> >
>> > stack backtrace:
>> > CPU: 1 PID: 4492 Comm: syz-executor715 Not tainted 4.17.0-rc2+ #23
>> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> > Google 01/01/2011
>> > Call Trace:
>> >  __dump_stack lib/dump_stack.c:77 [inline]
>> >  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>> >  print_circular_bug.isra.36.cold.54+0x1bd/0x27d
>> > kernel/locking/lockdep.c:1223
>> >  check_prev_add kernel/locking/lockdep.c:1863 [inline]
>> >  check_prevs_add kernel/locking/lockdep.c:1976 [inline]
>> >  validate_chain kernel/locking/lockdep.c:2417 [inline]
>> >  __lock_acquire+0x343e/0x5140 kernel/locking/lockdep.c:3431
>> >  lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
>> >  percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline]
>> >  percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
>> >  __sb_start_write+0x1e9/0x300 fs/super.c:1385
>> >  file_start_write include/linux/fs.h:2718 [inline]
>> >  vfs_fallocate+0x5be/0x8d0 fs/open.c:318
>> >  ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
>> >  ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
>> >  vfs_ioctl fs/ioctl.c:46 [inline]
>> >  file_ioctl fs/ioctl.c:500 [inline]
>> >  do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
>> >  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
>> >  __do_sys_ioctl fs/ioctl.c:708 [inline]
>> >  __se_sys_ioctl fs/ioctl.c:706 [inline]
>> >  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
>> >  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> >  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> > RIP: 0033:0x440179
>> > RSP: 002b:00007ffc165d4a28 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
>> > RAX: ffffffffffffffda RBX: 6873612f7665642f RCX: 0000000000440179
>> > RDX: 0000000000000000 RSI: 000000000000770a RDI: 0000000000000004
>> > RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
>> > R10: 0000000000000004 R11: 0000000000000217 R12: 00000000004016a0
>> > R13: 0000000000401730 R14: 0000000000000000 R15: 0000000000000000
>> > random: crng init done
>> >
>> >
>> > ---
>> > This bug is generated by a dumb bot. It may contain errors.
>> > See https://goo.gl/tpsmEJ for details.
>> > Direct all questions to syzkaller@googlegroups.com.
>> >
>> > syzbot will keep track of this bug report.
>> > If you forgot to add the Reported-by tag, once the fix for this bug is
>> > merged
>> > into any tree, please reply to this email with:
>> > #syz fix: exact-commit-title
>> > If you want to test a patch for this bug, please reply with:
>> > #syz test: git://repo/address.git branch
>> > and provide the patch inline or as an attachment.
>> > To mark this as a duplicate of another syzbot report, please reply with:
>> > #syz dup: exact-subject-of-another-report
>> > If it's a one-off invalid bug report, please reply with:
>> > #syz invalid
>> > Note: if the crash happens again, it will cause creation of a new bug
>> > report.
>> > Note: all commands must start from beginning of the line in the email body.
>>
>> Looks like yet another locking bug in ashmem.  ashmem_mutex normally ranks below
>> mmap_sem, but ashmem_shrink_scan() inverts that order, via the
>> file_start_write() in vfs_fallocate().
>>
>> - Eric

[-- Attachment #2: ashmem.patch --]
[-- Type: text/x-patch, Size: 3279 bytes --]

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 90a8a9f1ac7d..1a890c43a10a 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -75,6 +75,17 @@ struct ashmem_range {
 /* LRU list of unpinned pages, protected by ashmem_mutex */
 static LIST_HEAD(ashmem_lru_list);
 
+static struct workqueue_struct *ashmem_wq;
+static atomic_t ashmem_shrink_inflight = ATOMIC_INIT(0);
+static DECLARE_WAIT_QUEUE_HEAD(ashmem_shrink_wait);
+
+struct ashmem_shrink_work {
+	struct work_struct work;
+	struct file *file;
+	loff_t start;
+	loff_t end;
+};
+
 /*
  * long lru_count - The count of pages on our LRU list.
  *
@@ -292,6 +303,7 @@ static ssize_t ashmem_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 	int ret = 0;
 
 	mutex_lock(&ashmem_mutex);
+	wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
 
 	/* If size is not set, or set to 0, always return EOF. */
 	if (asma->size == 0)
@@ -359,6 +371,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
 	int ret = 0;
 
 	mutex_lock(&ashmem_mutex);
+	wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
 
 	/* user needs to SET_SIZE before mapping */
 	if (!asma->size) {
@@ -421,6 +434,19 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
 	return ret;
 }
 
+static void ashmem_shrink_worker(struct work_struct *work)
+{
+	struct ashmem_shrink_work *w = container_of(work, typeof(*w), work);
+
+	w->file->f_op->fallocate(w->file,
+				 FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+				 w->start, w->end - w->start);
+	fput(w->file);
+	kfree(w);
+	if (atomic_dec_and_test(&ashmem_shrink_inflight))
+		wake_up_all(&ashmem_shrink_wait);
+}
+
 /*
  * ashmem_shrink - our cache shrinker, called from mm/vmscan.c
  *
@@ -449,12 +475,18 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 		return -1;
 
 	list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) {
-		loff_t start = range->pgstart * PAGE_SIZE;
-		loff_t end = (range->pgend + 1) * PAGE_SIZE;
+		struct ashmem_shrink_work *w = kzalloc(sizeof(*w), GFP_ATOMIC);
+
+		if (!w)
+			break;
+		INIT_WORK(&w->work, ashmem_shrink_worker);
+		w->file = range->asma->file;
+		get_file(w->file);
+		w->start = range->pgstart * PAGE_SIZE;
+		w->end = (range->pgend + 1) * PAGE_SIZE;
+		atomic_inc(&ashmem_shrink_inflight);
+		queue_work(ashmem_wq, &w->work);
 
-		range->asma->file->f_op->fallocate(range->asma->file,
-				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
-				start, end - start);
 		range->purged = ASHMEM_WAS_PURGED;
 		lru_del(range);
 
@@ -713,6 +745,7 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
 		return -EFAULT;
 
 	mutex_lock(&ashmem_mutex);
+	wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
 
 	if (!asma->file)
 		goto out_unlock;
@@ -883,8 +916,15 @@ static int __init ashmem_init(void)
 		goto out_free2;
 	}
 
+	ashmem_wq = alloc_workqueue("ashmem_wq", WQ_MEM_RECLAIM, 0);
+	if (!ashmem_wq) {
+		pr_err("failed to create workqueue\n");
+		goto out_demisc;
+	}
+
 	ret = register_shrinker(&ashmem_shrinker);
 	if (ret) {
+		destroy_workqueue(ashmem_wq);
 		pr_err("failed to register shrinker!\n");
 		goto out_demisc;
 	}

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: possible deadlock in vfs_fallocate
  2019-01-22 13:58     ` Dmitry Vyukov
@ 2019-01-22 14:26       ` syzbot
  0 siblings, 0 replies; 5+ messages in thread
From: syzbot @ 2019-01-22 14:26 UTC (permalink / raw)
  To: arve, devel, dvyukov, ebiggers3, gregkh, joelaf, linux-fsdevel,
	linux-kernel, maco, penguin-kernel, syzkaller-bugs, tkjos, tkjos

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger  
crash:

Reported-and-tested-by:  
syzbot+148c2885d71194f18d28@syzkaller.appspotmail.com

Tested on:

commit:         48b161983ae5 Merge tag 'xarray-5.0-rc3' of git://git.infra..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=dd3a020d055fa2e8
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16e6d908c00000

Note: testing is done by a robot and is best-effort only.

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2019-01-22 14:26 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-04-29 17:00 possible deadlock in vfs_fallocate syzbot
2018-05-09  7:57 ` Eric Biggers
2018-05-09 16:56   ` Todd Kjos
2019-01-22 13:58     ` Dmitry Vyukov
2019-01-22 14:26       ` syzbot

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