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From: Eric Biggers <ebiggers@kernel.org>
To: linux-cifs@vger.kernel.org
Cc: linux-ext4@vger.kernel.org, syzkaller-bugs@googlegroups.com,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2] cifs: clear PF_MEMALLOC before exiting demultiplex thread
Date: Sat,  7 Mar 2020 22:16:11 -0800	[thread overview]
Message-ID: <20200308061611.1185481-1-ebiggers@kernel.org> (raw)
In-Reply-To: <20200308043645.1034870-1-ebiggers@kernel.org>

From: Eric Biggers <ebiggers@google.com>

Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set
during do_exit().  That can confuse things.  For example, if BSD process
accounting is enabled, then it's possible for do_exit() to end up
calling ext4_write_inode().  That triggers the
WARN_ON_ONCE(current->flags & PF_MEMALLOC) there, as it assumes
(appropriately) that inodes aren't written when allocating memory.

This case was reported by syzbot at
https://lkml.kernel.org/r/0000000000000e7156059f751d7b@google.com.

Fix this in cifs_demultiplex_thread() by using the helper functions to
save and restore PF_MEMALLOC.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---

v2: added missing include of <linux/sched/mm.h>
    (I missed that I didn't actually have CONFIG_CIFS set...)

 fs/cifs/connect.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 4804d1df8c1c..97b8eb585cf9 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -21,6 +21,7 @@
 #include <linux/fs.h>
 #include <linux/net.h>
 #include <linux/string.h>
+#include <linux/sched/mm.h>
 #include <linux/sched/signal.h>
 #include <linux/list.h>
 #include <linux/wait.h>
@@ -1164,8 +1165,9 @@ cifs_demultiplex_thread(void *p)
 	struct task_struct *task_to_wake = NULL;
 	struct mid_q_entry *mids[MAX_COMPOUND];
 	char *bufs[MAX_COMPOUND];
+	unsigned int noreclaim_flag;
 
-	current->flags |= PF_MEMALLOC;
+	noreclaim_flag = memalloc_noreclaim_save();
 	cifs_dbg(FYI, "Demultiplex PID: %d\n", task_pid_nr(current));
 
 	length = atomic_inc_return(&tcpSesAllocCount);
@@ -1320,6 +1322,7 @@ cifs_demultiplex_thread(void *p)
 		set_current_state(TASK_RUNNING);
 	}
 
+	memalloc_noreclaim_restore(noreclaim_flag);
 	module_put_and_exit(0);
 }
 
-- 
2.25.1


  reply	other threads:[~2020-03-08  6:17 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-26  6:57 WARNING in ext4_write_inode syzbot
2020-03-08  4:35 ` [PATCH] xfs: clear PF_MEMALLOC before exiting xfsaild thread Eric Biggers
2020-03-08 23:03   ` Dave Chinner
2020-03-09  1:04     ` Eric Biggers
2020-03-09  4:34       ` [PATCH v2] " Eric Biggers
2020-03-09 10:57         ` Brian Foster
2020-03-09 16:24         ` Darrick J. Wong
2020-03-09 18:04           ` Eric Biggers
2020-03-09 18:13             ` Darrick J. Wong
2020-03-09 18:57               ` [PATCH v3] " Eric Biggers
2020-03-10 15:47                 ` Darrick J. Wong
2020-03-11  6:34                 ` Christoph Hellwig
2020-03-12 22:20           ` [PATCH v2] " Eric Biggers
2020-03-08  4:36 ` [PATCH] cifs: clear PF_MEMALLOC before exiting demultiplex thread Eric Biggers
2020-03-08  6:16   ` Eric Biggers [this message]
2020-03-08 18:43     ` [PATCH v2] " Steve French
2020-03-09  5:56       ` Eric Biggers
2020-03-09  5:58         ` [PATCH v3] " Eric Biggers

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