diff mbox

fs-writeback: drop wb->list_lock during blk_finish_plug()

Message ID 20150909152323.GB3784@ret.masoncoding.com
State New, archived
Headers show

Commit Message

Chris Mason Sept. 9, 2015, 3:23 p.m. UTC
Commit d353d7587 added a plug/finish_plug pair to writeback_sb_inodes,
but writeback_sb_inodes has a horrible secret...it's called with the
wb->list_lock held.

Btrfs raid5/6 and MD raid10 have horrible secrets of their own...they
both do allocations in their unplug callbacks.

None of the options to fix it are very pretty.  We don't want to kick
off workers for all of these unplugs, and the lock doesn't look hot
enough to justify bigger restructuring.

[ 2854.025042] BUG: sleeping function called from invalid context at mm/page_alloc.c:3189
[ 2854.041366] in_atomic(): 1, irqs_disabled(): 0, pid: 145562, name: kworker/u66:15
[ 2854.056813] INFO: lockdep is turned off.
[ 2854.064870] CPU: 13 PID: 145562 Comm: kworker/u66:15 Not tainted 4.2.0-mason+ #1
[ 2854.080082] Hardware name: ZTSYSTEMS Echo Ridge T4  /A9DRPF-10D, BIOS 1.07 05/10/2012
[ 2854.096211] Workqueue: writeback wb_workfn (flush-btrfs-244)
[ 2854.107821]  ffffffff81a2bbee ffff880ee09a7598 ffffffff813307bb ffff880ee09a7598
[ 2854.123162]  ffff881010d1ca00 ffff880ee09a75c8 ffffffff81086615 0000000000000000
[ 2854.138556]  0000000000000000 0000000000000c75 ffffffff81a2bbee ffff880ee09a75f8
[ 2854.153936] Call Trace:
[ 2854.181101]  [<ffffffff81086722>] __might_sleep+0x52/0x90
[ 2854.192136]  [<ffffffff8116d2b4>] __alloc_pages_nodemask+0x344/0xbe0
[ 2854.229682]  [<ffffffff811b54aa>] alloc_pages_current+0x10a/0x1e0
[ 2854.255508]  [<ffffffffa0663f19>] full_stripe_write+0x59/0xc0 [btrfs]
[ 2854.268600]  [<ffffffffa0663fb9>] __raid56_parity_write+0x39/0x60 [btrfs]
[ 2854.282385]  [<ffffffffa06640fb>] run_plug+0x11b/0x140 [btrfs]
[ 2854.294259]  [<ffffffffa0664143>] btrfs_raid_unplug+0x23/0x70 [btrfs]
[ 2854.307334]  [<ffffffff81307622>] blk_flush_plug_list+0x82/0x1f0
[ 2854.319542]  [<ffffffff813077c4>] blk_finish_plug+0x34/0x50
[ 2854.330878]  [<ffffffff812079c2>] writeback_sb_inodes+0x122/0x580
[ 2854.343256]  [<ffffffff81208016>] wb_writeback+0x136/0x4e0

Signed-off-by: Chris Mason <clm@fb.com>
---
 fs/fs-writeback.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Jens Axboe Sept. 11, 2015, 6:49 p.m. UTC | #1
On Wed, Sep 09 2015, Chris Mason wrote:
> Commit d353d7587 added a plug/finish_plug pair to writeback_sb_inodes,
> but writeback_sb_inodes has a horrible secret...it's called with the
> wb->list_lock held.
> 
> Btrfs raid5/6 and MD raid10 have horrible secrets of their own...they
> both do allocations in their unplug callbacks.
> 
> None of the options to fix it are very pretty.  We don't want to kick
> off workers for all of these unplugs, and the lock doesn't look hot
> enough to justify bigger restructuring.
> 
> [ 2854.025042] BUG: sleeping function called from invalid context at mm/page_alloc.c:3189
> [ 2854.041366] in_atomic(): 1, irqs_disabled(): 0, pid: 145562, name: kworker/u66:15
> [ 2854.056813] INFO: lockdep is turned off.
> [ 2854.064870] CPU: 13 PID: 145562 Comm: kworker/u66:15 Not tainted 4.2.0-mason+ #1
> [ 2854.080082] Hardware name: ZTSYSTEMS Echo Ridge T4  /A9DRPF-10D, BIOS 1.07 05/10/2012
> [ 2854.096211] Workqueue: writeback wb_workfn (flush-btrfs-244)
> [ 2854.107821]  ffffffff81a2bbee ffff880ee09a7598 ffffffff813307bb ffff880ee09a7598
> [ 2854.123162]  ffff881010d1ca00 ffff880ee09a75c8 ffffffff81086615 0000000000000000
> [ 2854.138556]  0000000000000000 0000000000000c75 ffffffff81a2bbee ffff880ee09a75f8
> [ 2854.153936] Call Trace:
> [ 2854.181101]  [<ffffffff81086722>] __might_sleep+0x52/0x90
> [ 2854.192136]  [<ffffffff8116d2b4>] __alloc_pages_nodemask+0x344/0xbe0
> [ 2854.229682]  [<ffffffff811b54aa>] alloc_pages_current+0x10a/0x1e0
> [ 2854.255508]  [<ffffffffa0663f19>] full_stripe_write+0x59/0xc0 [btrfs]
> [ 2854.268600]  [<ffffffffa0663fb9>] __raid56_parity_write+0x39/0x60 [btrfs]
> [ 2854.282385]  [<ffffffffa06640fb>] run_plug+0x11b/0x140 [btrfs]
> [ 2854.294259]  [<ffffffffa0664143>] btrfs_raid_unplug+0x23/0x70 [btrfs]
> [ 2854.307334]  [<ffffffff81307622>] blk_flush_plug_list+0x82/0x1f0
> [ 2854.319542]  [<ffffffff813077c4>] blk_finish_plug+0x34/0x50
> [ 2854.330878]  [<ffffffff812079c2>] writeback_sb_inodes+0x122/0x580
> [ 2854.343256]  [<ffffffff81208016>] wb_writeback+0x136/0x4e0
> 
> Signed-off-by: Chris Mason <clm@fb.com>

Reviewed-by: Jens Axboe <axboe@fb.com>
diff mbox

Patch

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index ae0f438..07c9c50 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1539,7 +1539,9 @@  static long writeback_sb_inodes(struct super_block *sb,
 				break;
 		}
 	}
+	spin_unlock(&wb->list_lock);
 	blk_finish_plug(&plug);
+	spin_lock(&wb->list_lock);
 	return wrote;
 }