This is a note to let you know that I have just added a patch titled
ext4: fix a potential deadlock in __ext4_es_shrink()
to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue
This patch is scheduled to be released in version 3.13.11.6.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From 64e2e7a802f63d1f40591cfd2bd5d6af3d438703 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso at mit.edu>
Date: Sat, 12 Jul 2014 15:32:24 -0400
Subject: ext4: fix a potential deadlock in __ext4_es_shrink()
commit 3f1f9b851311a76226140b55b1ea22111234a7c2 upstream.
This fixes the following lockdep complaint:
[ INFO: possible circular locking dependency detected ]
3.16.0-rc2-mm1+ #7 Tainted: G O
-------------------------------------------------------
kworker/u24:0/4356 is trying to acquire lock:
(&(&sbi->s_es_lru_lock)->rlock){+.+.-.}, at: [<ffffffff81285fff>] __ext4_es_shrink+0x4f/0x2e0
but task is already holding lock:
(&ei->i_es_lock){++++-.}, at: [<ffffffff81286961>] ext4_es_insert_extent+0x71/0x180
which lock already depends on the new lock.
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&ei->i_es_lock);
lock(&(&sbi->s_es_lru_lock)->rlock);
lock(&ei->i_es_lock);
lock(&(&sbi->s_es_lru_lock)->rlock);
*** DEADLOCK ***
6 locks held by kworker/u24:0/4356:
#0: ("writeback"){.+.+.+}, at: [<ffffffff81071d00>] process_one_work+0x180/0x560
#1: ((&(&wb->dwork)->work)){+.+.+.}, at: [<ffffffff81071d00>] process_one_work+0x180/0x560
#2: (&type->s_umount_key#22){++++++}, at: [<ffffffff811a9c74>] grab_super_passive+0x44/0x90
#3: (jbd2_handle){+.+...}, at: [<ffffffff812979f9>] start_this_handle+0x189/0x5f0
#4: (&ei->i_data_sem){++++..}, at: [<ffffffff81247062>] ext4_map_blocks+0x132/0x550
#5: (&ei->i_es_lock){++++-.}, at: [<ffffffff81286961>] ext4_es_insert_extent+0x71/0x180
stack backtrace:
CPU: 0 PID: 4356 Comm: kworker/u24:0 Tainted: G O 3.16.0-rc2-mm1+ #7
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Workqueue: writeback bdi_writeback_workfn (flush-253:0)
ffffffff8213dce0 ffff880014b07538 ffffffff815df0bb 0000000000000007
ffffffff8213e040 ffff880014b07588 ffffffff815db3dd ffff880014b07568
ffff880014b07610 ffff88003b868930 ffff88003b868908 ffff88003b868930
Call Trace:
[<ffffffff815df0bb>] dump_stack+0x4e/0x68
[<ffffffff815db3dd>] print_circular_bug+0x1fb/0x20c
[<ffffffff810a7a3e>] __lock_acquire+0x163e/0x1d00
[<ffffffff815e89dc>] ? retint_restore_args+0xe/0xe
[<ffffffff815ddc7b>] ? __slab_alloc+0x4a8/0x4ce
[<ffffffff81285fff>] ? __ext4_es_shrink+0x4f/0x2e0
[<ffffffff810a8707>] lock_acquire+0x87/0x120
[<ffffffff81285fff>] ? __ext4_es_shrink+0x4f/0x2e0
[<ffffffff8128592d>] ? ext4_es_free_extent+0x5d/0x70
[<ffffffff815e6f09>] _raw_spin_lock+0x39/0x50
[<ffffffff81285fff>] ? __ext4_es_shrink+0x4f/0x2e0
[<ffffffff8119760b>] ? kmem_cache_alloc+0x18b/0x1a0
[<ffffffff81285fff>] __ext4_es_shrink+0x4f/0x2e0
[<ffffffff812869b8>] ext4_es_insert_extent+0xc8/0x180
[<ffffffff812470f4>] ext4_map_blocks+0x1c4/0x550
[<ffffffff8124c4c4>] ext4_writepages+0x6d4/0xd00
...
Reported-by: Minchan Kim <minchan at kernel.org>
Signed-off-by: Theodore Ts'o <tytso at mit.edu>
Reported-by: Minchan Kim <minchan at kernel.org>
Cc: Zheng Liu <gnehzuil.liu at gmail.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
fs/ext4/extents_status.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 3981ff7..171b9fa 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -962,10 +962,10 @@ retry:
continue;
}
- if (ei->i_es_lru_nr == 0 || ei == locked_ei)
+ if (ei->i_es_lru_nr == 0 || ei == locked_ei ||
+ !write_trylock(&ei->i_es_lock))
continue;
- write_lock(&ei->i_es_lock);
shrunk = __es_try_to_reclaim_extents(ei, nr_to_scan);
if (ei->i_es_lru_nr == 0)
list_del_init(&ei->i_es_lru);
--
1.9.1