From: Theodore Ts'o Subject: [PATCH] ext4: fix a potential deadlock in __ext4_es_shrink() Date: Sat, 12 Jul 2014 15:33:23 -0400 Message-ID: <1405193603-15614-1-git-send-email-tytso@mit.edu> References: <20140707233326.GA6076@bbox> Cc: Minchan Kim , Theodore Ts'o , stable@vger.kernel.org, Zheng Liu To: Ext4 Developers List Return-path: In-Reply-To: <20140707233326.GA6076@bbox> Sender: stable-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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: [] __ext4_es_shrink+0x4f/0x2e0 but task is already holding lock: (&ei->i_es_lock){++++-.}, at: [] 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: [] process_one_work+0x180/0x560 #1: ((&(&wb->dwork)->work)){+.+.+.}, at: [] process_one_work+0x180/0x560 #2: (&type->s_umount_key#22){++++++}, at: [] grab_super_passive+0x44/0x90 #3: (jbd2_handle){+.+...}, at: [] start_this_handle+0x189/0x5f0 #4: (&ei->i_data_sem){++++..}, at: [] ext4_map_blocks+0x132/0x550 #5: (&ei->i_es_lock){++++-.}, at: [] 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: [] dump_stack+0x4e/0x68 [] print_circular_bug+0x1fb/0x20c [] __lock_acquire+0x163e/0x1d00 [] ? retint_restore_args+0xe/0xe [] ? __slab_alloc+0x4a8/0x4ce [] ? __ext4_es_shrink+0x4f/0x2e0 [] lock_acquire+0x87/0x120 [] ? __ext4_es_shrink+0x4f/0x2e0 [] ? ext4_es_free_extent+0x5d/0x70 [] _raw_spin_lock+0x39/0x50 [] ? __ext4_es_shrink+0x4f/0x2e0 [] ? kmem_cache_alloc+0x18b/0x1a0 [] __ext4_es_shrink+0x4f/0x2e0 [] ext4_es_insert_extent+0xc8/0x180 [] ext4_map_blocks+0x1c4/0x550 [] ext4_writepages+0x6d4/0xd00 ... Reported-by: Minchan Kim Signed-off-by: Theodore Ts'o Reported-by: Minchan Kim Cc: stable@vger.kernel.org Cc: Zheng Liu --- 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 3f5c188..0b7e28e 100644 --- a/fs/ext4/extents_status.c +++ b/fs/ext4/extents_status.c @@ -966,10 +966,10 @@ 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); -- 2.0.0