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From: Andreas Gruenbacher <agruenba@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Paul Mackerras <paulus@ozlabs.org>
Cc: Jan Kara <jack@suse.cz>, Matthew Wilcox <willy@infradead.org>,
	cluster-devel@redhat.com, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com,
	Andreas Gruenbacher <agruenba@redhat.com>,
	kvm-ppc@vger.kernel.org
Subject: [PATCH v5 00/12] gfs2: Fix mmap + page fault deadlocks
Date: Tue,  3 Aug 2021 21:18:06 +0200	[thread overview]
Message-ID: <20210803191818.993968-1-agruenba@redhat.com> (raw)

Hi all,

here's another update on top of v5.14-rc4.  There seems to be a bug in
get_user_pages_fast when called with FOLL_FAST_ONLY; please see below.

Changes:

 * Change fault_in_pages_{readable,writeable} to return the number of
   bytes that should be accessible instead of failing outright when
   part of the requested region cannot be faulted in.  Change
   iov_iter_fault_in_readable to those same semantics.

 * Add fault_in_iov_iter_writeable for safely faulting in pages for
   writing without modifying the pages.


With this patch queue, fstest generic/208 (aio-dio-invalidate-failure.c)
endlessly spins in gfs2_file_direct_write.  It looks as if there's a bug
in get_user_pages_fast when called with FOLL_FAST_ONLY:

 (1) The test case performs an aio write into a 32 MB buffer.

 (2) The buffer is initially not in memory, so when iomap_dio_rw() ->
     ... -> bio_iov_iter_get_pages() is called with the iter->noio flag
     set, we get to get_user_pages_fast() with FOLL_FAST_ONLY set.
     get_user_pages_fast() returns 0, which causes
     bio_iov_iter_get_pages to return -EFAULT.

 (3) Then gfs2_file_direct_write faults in the entire buffer with
     fault_in_iov_iter_readable(), which succeeds.

 (4) With the buffer in memory, we retry the iomap_dio_rw() ->
     ... -> bio_iov_iter_get_pages() -> ... -> get_user_pages_fast().
     This should succeed now, but get_user_pages_fast() still returns 0.

 (5) Thus we end up in step (3) again.

The buffered writes generic/208 performs are unrelated to this hang.


Apart from the generic/208 hang, gfs2 still needs a better strategy for
faulting in more reasonable chunks of memory at a time and for resuming
requests after faulting in pages.  We've got some of the pieces in place
for safely allowing that, but more work remains to be done.


For immediate consideration by Al Viro:

  iov_iter: Fix iov_iter_get_pages{,_alloc} page fault return value


For immediate consideration by Paul Mackerras:

  powerpc/kvm: Fix kvm_use_magic_page


Thanks,
Andreas


Andreas Gruenbacher (12):
  iov_iter: Fix iov_iter_get_pages{,_alloc} page fault return value
  powerpc/kvm: Fix kvm_use_magic_page
  Turn fault_in_pages_{readable,writeable} into
    fault_in_{readable,writeable}
  Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable
  iov_iter: Introduce fault_in_iov_iter_writeable
  gfs2: Add wrapper for iomap_file_buffered_write
  gfs2: Fix mmap + page fault deadlocks for buffered I/O
  iomap: Fix iomap_dio_rw return value for user copies
  iomap: Support restarting direct I/O requests after user copy failures
  iomap: Add done_before argument to iomap_dio_rw
  iov_iter: Introduce noio flag to disable page faults
  gfs2: Fix mmap + page fault deadlocks for direct I/O

 arch/powerpc/kernel/kvm.c           |   3 +-
 arch/powerpc/kernel/signal_32.c     |   4 +-
 arch/powerpc/kernel/signal_64.c     |   2 +-
 arch/x86/kernel/fpu/signal.c        |   8 +-
 drivers/gpu/drm/armada/armada_gem.c |   7 +-
 fs/btrfs/file.c                     |   8 +-
 fs/btrfs/ioctl.c                    |   7 +-
 fs/ext4/file.c                      |   5 +-
 fs/f2fs/file.c                      |   6 +-
 fs/fuse/file.c                      |   2 +-
 fs/gfs2/file.c                      |  95 ++++++++++++++++++++---
 fs/iomap/buffered-io.c              |   2 +-
 fs/iomap/direct-io.c                |  28 +++++--
 fs/ntfs/file.c                      |   2 +-
 fs/xfs/xfs_file.c                   |   6 +-
 fs/zonefs/super.c                   |   4 +-
 include/linux/iomap.h               |  11 ++-
 include/linux/pagemap.h             |  58 +-------------
 include/linux/uio.h                 |   4 +-
 lib/iov_iter.c                      | 107 ++++++++++++++++++++------
 mm/filemap.c                        |   4 +-
 mm/gup.c                            | 113 ++++++++++++++++++++++++++++
 22 files changed, 360 insertions(+), 126 deletions(-)

-- 
2.26.3


             reply	other threads:[~2021-08-03 19:18 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03 19:18 Andreas Gruenbacher [this message]
2021-08-03 19:18 ` [PATCH v5 01/12] iov_iter: Fix iov_iter_get_pages{,_alloc} page fault return value Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 02/12] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 03/12] Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable} Andreas Gruenbacher
2021-08-03 19:43   ` Linus Torvalds
2021-08-03 20:57   ` Al Viro
2021-08-03 21:38     ` Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 04/12] Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 05/12] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-08-04 15:24   ` Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 06/12] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 07/12] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 08/12] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 09/12] iomap: Support restarting direct I/O requests after user copy failures Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 10/12] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 11/12] iov_iter: Introduce noio flag to disable page faults Andreas Gruenbacher
2021-08-03 19:18 ` [PATCH v5 12/12] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-08-03 19:45 ` [PATCH v5 00/12] gfs2: Fix mmap + page fault deadlocks Linus Torvalds
2021-08-16 19:14   ` Andreas Gruenbacher
2021-08-18 21:49     ` Linus Torvalds
2021-08-19 19:40       ` Andreas Gruenbacher
2021-08-19 20:14         ` Linus Torvalds
2021-08-19 21:39           ` Andreas Gruenbacher

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