Note: this will probably need to be sent to Linus as an emergency
bugfix ASAP, since it was introduced in 3.1-rc1, so it represents a
regression.
Jiayingz, I'd appreciate if you could review this, since this is a
partial undo of commit 2581fdc810, which you authored. I don't think
taking out the call to ext4_flush_complted_IO() should should cause any
problems, since it should only delay how long it takes for an inode to
be evicted, and in some cases we are already waiting for a truncate or
journal commit to complete. But I don't want to take any chances, so a
second pair of eyes would be appreciated. Thanks!!
- Ted
>From 18271e31ece46955c0fd61e726fa7540fddf8924 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@xxxxxxx>
Date: Thu, 25 Aug 2011 23:26:01 -0400
Subject: [PATCH] ext4: fix potential deadlock in ext4_evict_inode()
Commit 2581fdc810 moved ext4_ioend_wait() from ext4_destroy_inode() to
ext4_evict_inode(). It also added code to explicitly call
ext4_flush_completed_IO(inode):
mutex_lock(&inode->i_mutex);
ext4_flush_completed_IO(inode);
mutex_unlock(&inode->i_mutex);
Unfortunately, we can't take the i_mutex lock in ext4_evict_inode()
without potentially causing a deadlock.
Fix this by removing the code sequence altogether. This may result in
ext4_evict_inode() taking longer to complete, but that's ok, we're not
in a rush here. That just means we have to wait until the workqueue
is scheduled, which is OK; there's nothing that says we have to do
this work on the current thread, which would require taking a lock
that might lead to a deadlock condition.
See Kernel Bugzilla #41682 for one example of the circular locking
problem that arise. Another one can be seen here:
=======================================================
[ INFO: possible circular locking dependency detected ]
3.1.0-rc3-00012-g2a22fc1 #1839
-------------------------------------------------------
dd/7677 is trying to acquire lock:
(&type->s_umount_key#18){++++..}, at: [<c021ea77>] writeback_inodes_sb_if_idle+0x26/0x3d
but task is already holding lock:
(&sb->s_type->i_mutex_key#3){+.+.+.}, at: [<c01d5956>] generic_file_aio_write+0x52/0xba
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&sb->s_type->i_mutex_key#3){+.+.+.}:
[<c018eb02>] lock_acquire+0x99/0xbd
[<c06a53b5>] __mutex_lock_common+0x33/0x2fb
[<c06a572b>] mutex_lock_nested+0x26/0x2f
[<c026c2db>] ext4_evict_inode+0x3e/0x2bd
[<c0214bb0>] evict+0x8e/0x131
[<c0214de6>] dispose_list+0x36/0x40
[<c0215239>] evict_inodes+0xcd/0xd5
[<c0204a23>] generic_shutdown_super+0x3d/0xaa
[<c0204ab2>] kill_block_super+0x22/0x5e
[<c0204cb8>] deactivate_locked_super+0x22/0x4e
[<c02055b2>] deactivate_super+0x3d/0x43
[<c0218427>] mntput_no_expire+0xda/0xdf
[<c0219486>] sys_umount+0x286/0x2ab
[<c02194bd>] sys_oldumount+0x12/0x14
[<c06a6ac5>] syscall_call+0x7/0xb
-> #0 (&type->s_umount_key#18){++++..}:
[<c018e262>] __lock_acquire+0x967/0xbd2
[<c018eb02>] lock_acquire+0x99/0xbd
[<c06a5991>] down_read+0x28/0x65
[<c021ea77>] writeback_inodes_sb_if_idle+0x26/0x3d
[<c0269630>] ext4_nonda_switch+0xd0/0xe1
[<c026e953>] ext4_da_write_begin+0x3c/0x1cf
[<c01d46ad>] generic_file_buffered_write+0xc0/0x1b4
[<c01d58d3>] __generic_file_aio_write+0x254/0x285
[<c01d596e>] generic_file_aio_write+0x6a/0xba
[<c026732f>] ext4_file_write+0x1d6/0x227
[<c0202789>] do_sync_write+0x8f/0xca
[<c02030d5>] vfs_write+0x85/0xe3
[<c02031d4>] sys_write+0x40/0x65
[<c06a6ac5>] syscall_call+0x7/0xb
https://bugzilla.kernel.org/show_bug.cgi?id=41682
Cc: stable@xxxxxxxxxx
Cc: Jiaying Zhang <jiayingz@xxxxxxxxxx>
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
---
fs/ext4/inode.c | 3 ---
1 files changed, 0 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 29b7148..cf0b515 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -121,9 +121,6 @@ void ext4_evict_inode(struct inode *inode)
trace_ext4_evict_inode(inode);
- mutex_lock(&inode->i_mutex);
- ext4_flush_completed_IO(inode);
- mutex_unlock(&inode->i_mutex);
ext4_ioend_wait(inode);
if (inode->i_nlink) {
--
1.7.4.1.22.gec8e1.dirty
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