* [PATCH] dm-snapshot: workaround for a lockdep warning
@ 2013-09-17 20:47 Mikulas Patocka
2013-09-17 23:24 ` Mikulas Patocka
0 siblings, 1 reply; 7+ messages in thread
From: Mikulas Patocka @ 2013-09-17 20:47 UTC (permalink / raw)
To: Alasdair G. Kergon, dm-devel
dm-snapshot: workaround for a lockdep warning
The kernel reports a lockdep warning if a snapshot is invalidated because
it runs out of space.
The lockdep warning was triggered by commit
0976dfc1d0cd80a4e9dfaf87bd8744612bde475a in the kernel 3.5.
The warning is false positive. The real cause for the warning is that the
lockdep engine treats different instances of md->lock as a single lock.
This patch is a workaround - we use flush_workqueue instead of flush_work.
This code path is not performance sensitive (it is called only on
initialization or invalidation), thus it doesn't matter that we flush the
whole workqueue.
The real fix for the problem would be to teach the lockdep engine to treat
different instances of md->lock as separate locks.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@kernel.org # 3.5+
Index: linux-2.6-devel/drivers/md/dm-snap-persistent.c
===================================================================
--- linux-2.6-devel.orig/drivers/md/dm-snap-persistent.c 2013-05-10 18:27:31.132358000 +0200
+++ linux-2.6-devel/drivers/md/dm-snap-persistent.c 2013-09-17 18:41:39.023940000 +0200
@@ -256,7 +256,7 @@
*/
INIT_WORK_ONSTACK(&req.work, do_metadata);
queue_work(ps->metadata_wq, &req.work);
- flush_work(&req.work);
+ flush_workqueue(ps->metadata_wq);
return req.result;
}
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] dm-snapshot: workaround for a lockdep warning
2013-09-17 20:47 [PATCH] dm-snapshot: workaround for a lockdep warning Mikulas Patocka
@ 2013-09-17 23:24 ` Mikulas Patocka
2013-09-18 0:08 ` Mikulas Patocka
0 siblings, 1 reply; 7+ messages in thread
From: Mikulas Patocka @ 2013-09-17 23:24 UTC (permalink / raw)
To: Alasdair G. Kergon, dm-devel, Stephen Boyd
BTW. this patch is no longer needed on 3.11 because md->io_lock was
removed there, so the false lockdep warning doesn't happen.
So we need to get this patch to stable trees 3.5 to 3.10, but not
upstream. How to push the patch there without pushing it upstream?
Mikulas
On Tue, 17 Sep 2013, Mikulas Patocka wrote:
> dm-snapshot: workaround for a lockdep warning
>
> The kernel reports a lockdep warning if a snapshot is invalidated because
> it runs out of space.
>
> The lockdep warning was triggered by commit
> 0976dfc1d0cd80a4e9dfaf87bd8744612bde475a in the kernel 3.5.
>
> The warning is false positive. The real cause for the warning is that the
> lockdep engine treats different instances of md->lock as a single lock.
>
> This patch is a workaround - we use flush_workqueue instead of flush_work.
> This code path is not performance sensitive (it is called only on
> initialization or invalidation), thus it doesn't matter that we flush the
> whole workqueue.
>
> The real fix for the problem would be to teach the lockdep engine to treat
> different instances of md->lock as separate locks.
>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: stable@kernel.org # 3.5+
>
> Index: linux-2.6-devel/drivers/md/dm-snap-persistent.c
> ===================================================================
> --- linux-2.6-devel.orig/drivers/md/dm-snap-persistent.c 2013-05-10 18:27:31.132358000 +0200
> +++ linux-2.6-devel/drivers/md/dm-snap-persistent.c 2013-09-17 18:41:39.023940000 +0200
> @@ -256,7 +256,7 @@
> */
> INIT_WORK_ONSTACK(&req.work, do_metadata);
> queue_work(ps->metadata_wq, &req.work);
> - flush_work(&req.work);
> + flush_workqueue(ps->metadata_wq);
>
> return req.result;
> }
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] dm-snapshot: workaround for a lockdep warning
2013-09-17 23:24 ` Mikulas Patocka
@ 2013-09-18 0:08 ` Mikulas Patocka
2013-09-18 6:57 ` Zdenek Kabelac
0 siblings, 1 reply; 7+ messages in thread
From: Mikulas Patocka @ 2013-09-18 0:08 UTC (permalink / raw)
To: Alasdair G. Kergon, Zdenek Kabelac, dm-devel, Stephen Boyd
On Tue, 17 Sep 2013, Mikulas Patocka wrote:
> BTW. this patch is no longer needed on 3.11 because md->io_lock was
> removed there, so the false lockdep warning doesn't happen.
>
> So we need to get this patch to stable trees 3.5 to 3.10, but not
> upstream. How to push the patch there without pushing it upstream?
>
> Mikulas
It's more complicated than that - the original Zdenek's report shows that
the false warning happened on kernel "3.11.1-300.fc20.x86_64+debug". But I
am not able to reproduce the bug on 3.11, I only reproduced it on 3.5-3.10
kernels.
Zdenek, could you reproduce the bug on kernel 3.11?
Mikulas
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] dm-snapshot: workaround for a lockdep warning
2013-09-18 0:08 ` Mikulas Patocka
@ 2013-09-18 6:57 ` Zdenek Kabelac
2013-09-18 15:57 ` Mikulas Patocka
0 siblings, 1 reply; 7+ messages in thread
From: Zdenek Kabelac @ 2013-09-18 6:57 UTC (permalink / raw)
To: Mikulas Patocka; +Cc: dm-devel, Stephen Boyd, Alasdair G. Kergon
Dne 18.9.2013 02:08, Mikulas Patocka napsal(a):
>
>
> On Tue, 17 Sep 2013, Mikulas Patocka wrote:
>
>> BTW. this patch is no longer needed on 3.11 because md->io_lock was
>> removed there, so the false lockdep warning doesn't happen.
>>
>> So we need to get this patch to stable trees 3.5 to 3.10, but not
>> upstream. How to push the patch there without pushing it upstream?
>>
>> Mikulas
>
> It's more complicated than that - the original Zdenek's report shows that
> the false warning happened on kernel "3.11.1-300.fc20.x86_64+debug". But I
> am not able to reproduce the bug on 3.11, I only reproduced it on 3.5-3.10
> kernels.
>
> Zdenek, could you reproduce the bug on kernel 3.11?
>
> Mikulas
>
Since I do not have clean 3.11 at my hands - I've reproduced it with my -rc6
kernel (few patches based on 8495e9c4a9616c9d19f23182d0536485902259db)
With enabled kmemleak=on lockdep.prove_locking=1 lockdep.lock_stat=1.
[ 173.077483] device-mapper: snapshots: Invalidating snapshot: Unable to
allocate exception.
[ 173.077928] ======================================================
[ 173.077930] [ INFO: possible circular locking dependency detected ]
[ 173.077934] 3.11.0-rc6-00153-gf4c4c6a #160 Not tainted
[ 173.077936] -------------------------------------------------------
[ 173.077939] kworker/u4:3/50 is trying to acquire lock:
[ 173.077941] ((&req.work)){+.+...}, at: [<ffffffff81067915>]
flush_work+0x5/0x60
[ 173.077954]
but task is already holding lock:
[ 173.077957] (&s->lock){++++..}, at: [<ffffffffa0a71b3a>]
snapshot_map+0x2aa/0x3a0 [dm_snapshot]
[ 173.077968]
which lock already depends on the new lock.
[ 173.077971]
the existing dependency chain (in reverse order) is:
[ 173.077974]
-> #1 (&s->lock){++++..}:
[ 173.077980] [<ffffffff810bd5e3>] lock_acquire+0x93/0x200
[ 173.077986] [<ffffffff8158df60>] _raw_spin_lock+0x40/0x80
[ 173.077991] [<ffffffff815849b9>] __slab_alloc.constprop.67+0x141/0x50d
[ 173.077996] [<ffffffff8118bd42>] kmem_cache_alloc+0x252/0x290
[ 173.078001] [<ffffffff8119f969>] create_object+0x39/0x310
[ 173.078006] [<ffffffff8157e2ae>] kmemleak_alloc+0x4e/0xb0
[ 173.078011] [<ffffffff8118b8b5>] kmem_cache_alloc_trace+0x105/0x2a0
[ 173.078015] [<ffffffff8121c502>] sysfs_open_file+0x1e2/0x240
[ 173.078021] [<ffffffff811a232b>] do_dentry_open+0x1fb/0x290
[ 173.078025] [<ffffffff811a2400>] finish_open+0x40/0x50
[ 173.078029] [<ffffffff811b3c9a>] do_last+0x4ca/0xe00
[ 173.078033] [<ffffffff811b468e>] path_openat+0xbe/0x6f0
[ 173.078037] [<ffffffff811b539a>] do_filp_open+0x3a/0x90
[ 173.078040] [<ffffffff811a37ee>] do_sys_open+0x12e/0x210
[ 173.078045] [<ffffffff811a38ee>] SyS_open+0x1e/0x20
[ 173.078049] [<ffffffff81597106>] system_call_fastpath+0x1a/0x1f
[ 173.078053]
-> #0 ((&req.work)){+.+...}:
[ 173.078060] [<ffffffff810bcac0>] __lock_acquire+0x1790/0x1af0
[ 173.078063] [<ffffffff810bd5e3>] lock_acquire+0x93/0x200
[ 173.078067] [<ffffffff81067946>] flush_work+0x36/0x60
[ 173.078071] [<ffffffffa0a72748>] chunk_io+0x118/0x150 [dm_snapshot]
[ 173.078076] [<ffffffffa0a727d9>] write_header+0x59/0x60 [dm_snapshot]
[ 173.078081] [<ffffffffa0a727f9>] persistent_drop_snapshot+0x19/0x30
[dm_snapshot]
[ 173.078086] [<ffffffffa0a6fe9c>]
__invalidate_snapshot.part.13+0x2c/0x70 [dm_snapshot]
[ 173.078091] [<ffffffffa0a719b7>] snapshot_map+0x127/0x3a0 [dm_snapshot]
[ 173.078096] [<ffffffffa0a4e7ee>] __map_bio+0x3e/0x1f0 [dm_mod]
[ 173.078104] [<ffffffffa0a4eb80>]
__clone_and_map_data_bio+0x150/0x230 [dm_mod]
[ 173.078109] [<ffffffffa0a4f08c>] __split_and_process_bio+0x38c/0x5a0
[dm_mod]
[ 173.078115] [<ffffffffa0a4f5a9>] dm_request+0x1b9/0x2f0 [dm_mod]
[ 173.078121] [<ffffffff813042b2>] generic_make_request+0xc2/0x110
[ 173.078127] [<ffffffff81304362>] submit_bio+0x62/0x130
[ 173.078131] [<ffffffff811e7ac8>] __mpage_writepage+0x448/0x680
[ 173.078136] [<ffffffff8114931b>] write_cache_pages+0x27b/0x630
[ 173.078142] [<ffffffff811e763a>] mpage_writepages+0x5a/0xa0
[ 173.078146] [<ffffffff812429d5>] ext2_writepages+0x15/0x20
[ 173.078151] [<ffffffff8114b081>] do_writepages+0x21/0x50
[ 173.078155] [<ffffffff811d27d0>] __writeback_single_inode+0x40/0x600
[ 173.078160] [<ffffffff811d3000>] writeback_sb_inodes+0x270/0x570
[ 173.078164] [<ffffffff811d339f>] __writeback_inodes_wb+0x9f/0xd0
[ 173.078168] [<ffffffff811d3743>] wb_writeback+0x373/0x5a0
[ 173.078172] [<ffffffff811d4094>] bdi_writeback_workfn+0x134/0x6d0
[ 173.078176] [<ffffffff8106993d>] process_one_work+0x1fd/0x6f0
[ 173.078180] [<ffffffff81069f53>] worker_thread+0x123/0x3b0
[ 173.078184] [<ffffffff81074a0e>] kthread+0xde/0xf0
[ 173.078188] [<ffffffff8159705c>] ret_from_fork+0x7c/0xb0
[ 173.078192]
other info that might help us debug this:
[ 173.078196] Possible unsafe locking scenario:
[ 173.078198] CPU0 CPU1
[ 173.078200] ---- ----
[ 173.078202] lock(&s->lock);
[ 173.078207] lock((&req.work));
[ 173.078211] lock(&s->lock);
[ 173.078215] lock((&req.work));
[ 173.078219]
*** DEADLOCK ***
[ 173.078222] 5 locks held by kworker/u4:3/50:
[ 173.078225] #0: (writeback){++++.+}, at: [<ffffffff810698db>]
process_one_work+0x19b/0x6f0
[ 173.078233] #1: ((&(&wb->dwork)->work)){+.+.+.}, at: [<ffffffff810698db>]
process_one_work+0x19b/0x6f0
[ 173.078242] #2: (&type->s_umount_key#30){++++..}, at:
[<ffffffff811a7f64>] grab_super_passive+0x44/0x90
[ 173.078252] #3: (&md->io_barrier){.+.+..}, at: [<ffffffffa0a4f335>]
dm_get_live_table+0x5/0xc0 [dm_mod]
[ 173.078263] #4: (&s->lock){++++..}, at: [<ffffffffa0a71b3a>]
snapshot_map+0x2aa/0x3a0 [dm_snapshot]
[ 173.078273]
stack backtrace:
[ 173.078277] CPU: 0 PID: 50 Comm: kworker/u4:3 Not tainted
3.11.0-rc6-00153-gf4c4c6a #160
[ 173.078280] Hardware name: LENOVO 6464CTO/6464CTO, BIOS 7LETC9WW (2.29 )
03/18/2011
[ 173.078284] Workqueue: writeback bdi_writeback_workfn (flush-253:3)
[ 173.078289] ffffffff82369540 ffff8801305732f8 ffffffff815869ad
ffffffff82369540
[ 173.078295] ffff880130573338 ffffffff815827ab ffff880130573390
ffff880130ab4ef8
[ 173.078301] 0000000000000004 ffff880130ab4ec0 ffff880130ab46e0
ffff880130ab4ef8
[ 173.078307] Call Trace:
[ 173.078312] [<ffffffff815869ad>] dump_stack+0x4e/0x82
[ 173.078317] [<ffffffff815827ab>] print_circular_bug+0x200/0x20f
[ 173.078322] [<ffffffff810bcac0>] __lock_acquire+0x1790/0x1af0
[ 173.078326] [<ffffffff810b78df>] ? trace_hardirqs_off_caller+0x1f/0xc0
[ 173.078330] [<ffffffff810b8089>] ? put_lock_stats.isra.27+0x29/0x40
[ 173.078334] [<ffffffff810bd5e3>] lock_acquire+0x93/0x200
[ 173.078338] [<ffffffff81067915>] ? flush_work+0x5/0x60
[ 173.078342] [<ffffffff81067946>] flush_work+0x36/0x60
[ 173.078346] [<ffffffff81067915>] ? flush_work+0x5/0x60
[ 173.078351] [<ffffffffa0a72748>] chunk_io+0x118/0x150 [dm_snapshot]
[ 173.078357] [<ffffffffa0a72600>] ? persistent_prepare_exception+0xa0/0xa0
[dm_snapshot]
[ 173.078363] [<ffffffffa0a727d9>] write_header+0x59/0x60 [dm_snapshot]
[ 173.078368] [<ffffffffa0a727f9>] persistent_drop_snapshot+0x19/0x30
[dm_snapshot]
[ 173.078373] [<ffffffffa0a6fe9c>] __invalidate_snapshot.part.13+0x2c/0x70
[dm_snapshot]
[ 173.078378] [<ffffffffa0a719b7>] snapshot_map+0x127/0x3a0 [dm_snapshot]
[ 173.078384] [<ffffffffa0a4e7ee>] __map_bio+0x3e/0x1f0 [dm_mod]
[ 173.078391] [<ffffffffa0a4eb80>] __clone_and_map_data_bio+0x150/0x230 [dm_mod]
[ 173.078397] [<ffffffffa0a4f08c>] __split_and_process_bio+0x38c/0x5a0 [dm_mod]
[ 173.078404] [<ffffffffa0a4f5a9>] dm_request+0x1b9/0x2f0 [dm_mod]
[ 173.078410] [<ffffffffa0a4f425>] ? dm_request+0x35/0x2f0 [dm_mod]
[ 173.078414] [<ffffffff813042b2>] generic_make_request+0xc2/0x110
[ 173.078419] [<ffffffff81304362>] submit_bio+0x62/0x130
[ 173.078423] [<ffffffff811e7ac8>] __mpage_writepage+0x448/0x680
[ 173.078429] [<ffffffff81084c2d>] ? get_parent_ip+0xd/0x50
[ 173.078433] [<ffffffff810baddb>] ? mark_held_locks+0xbb/0x140
[ 173.078438] [<ffffffff8114906c>] ? clear_page_dirty_for_io+0xac/0xe0
[ 173.078442] [<ffffffff810baf75>] ? trace_hardirqs_on_caller+0x115/0x1e0
[ 173.078446] [<ffffffff8114931b>] write_cache_pages+0x27b/0x630
[ 173.078450] [<ffffffff810ba933>] ? check_irq_usage+0x83/0xc0
[ 173.078455] [<ffffffff811e7680>] ? mpage_writepages+0xa0/0xa0
[ 173.078459] [<ffffffff81243620>] ? ext2_get_blocks+0xa90/0xa90
[ 173.078463] [<ffffffff811e763a>] mpage_writepages+0x5a/0xa0
[ 173.078467] [<ffffffff81243620>] ? ext2_get_blocks+0xa90/0xa90
[ 173.078472] [<ffffffff812429d5>] ext2_writepages+0x15/0x20
[ 173.078476] [<ffffffff8114b081>] do_writepages+0x21/0x50
[ 173.078481] [<ffffffff811d27d0>] __writeback_single_inode+0x40/0x600
[ 173.078485] [<ffffffff811d3000>] writeback_sb_inodes+0x270/0x570
[ 173.078489] [<ffffffff811d339f>] __writeback_inodes_wb+0x9f/0xd0
[ 173.078494] [<ffffffff811d3743>] wb_writeback+0x373/0x5a0
[ 173.078498] [<ffffffff811d4094>] bdi_writeback_workfn+0x134/0x6d0
[ 173.078503] [<ffffffff810698db>] ? process_one_work+0x19b/0x6f0
[ 173.078507] [<ffffffff8106993d>] process_one_work+0x1fd/0x6f0
[ 173.078511] [<ffffffff810698db>] ? process_one_work+0x19b/0x6f0
[ 173.078515] [<ffffffff81069f53>] worker_thread+0x123/0x3b0
[ 173.078519] [<ffffffff81069e30>] ? process_one_work+0x6f0/0x6f0
[ 173.078523] [<ffffffff81074a0e>] kthread+0xde/0xf0
[ 173.078529] [<ffffffff81074930>] ? insert_kthread_work+0x70/0x70
[ 173.078532] [<ffffffff8159705c>] ret_from_fork+0x7c/0xb0
[ 173.078537] [<ffffffff81074930>] ? insert_kthread_work+0x70/0x70
[ 173.120355] quiet_error: 1206 callbacks suppressed
[ 173.120362] Buffer I/O error on device dm-3, logical block 34
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] dm-snapshot: workaround for a lockdep warning
2013-09-18 6:57 ` Zdenek Kabelac
@ 2013-09-18 15:57 ` Mikulas Patocka
2013-09-18 19:07 ` Zdenek Kabelac
0 siblings, 1 reply; 7+ messages in thread
From: Mikulas Patocka @ 2013-09-18 15:57 UTC (permalink / raw)
To: Zdenek Kabelac; +Cc: dm-devel, Stephen Boyd, Alasdair G. Kergon
On Wed, 18 Sep 2013, Zdenek Kabelac wrote:
> Dne 18.9.2013 02:08, Mikulas Patocka napsal(a):
> >
> >
> > On Tue, 17 Sep 2013, Mikulas Patocka wrote:
> >
> > > BTW. this patch is no longer needed on 3.11 because md->io_lock was
> > > removed there, so the false lockdep warning doesn't happen.
> > >
> > > So we need to get this patch to stable trees 3.5 to 3.10, but not
> > > upstream. How to push the patch there without pushing it upstream?
> > >
> > > Mikulas
> >
> > It's more complicated than that - the original Zdenek's report shows that
> > the false warning happened on kernel "3.11.1-300.fc20.x86_64+debug". But I
> > am not able to reproduce the bug on 3.11, I only reproduced it on 3.5-3.10
> > kernels.
> >
> > Zdenek, could you reproduce the bug on kernel 3.11?
> >
> > Mikulas
> >
>
>
> Since I do not have clean 3.11 at my hands - I've reproduced it with my -rc6
> kernel (few patches based on 8495e9c4a9616c9d19f23182d0536485902259db)
> With enabled kmemleak=on lockdep.prove_locking=1 lockdep.lock_stat=1.
So - try this patch and tell me if it fixes the problem:
Index: linux-2.6-devel/drivers/md/dm-snap-persistent.c
===================================================================
--- linux-2.6-devel.orig/drivers/md/dm-snap-persistent.c 2013-05-10 18:27:31.132358000 +0200
+++ linux-2.6-devel/drivers/md/dm-snap-persistent.c 2013-09-17 18:41:39.023940000 +0200
@@ -256,7 +256,7 @@
*/
INIT_WORK_ONSTACK(&req.work, do_metadata);
queue_work(ps->metadata_wq, &req.work);
- flush_work(&req.work);
+ flush_workqueue(ps->metadata_wq);
return req.result;
}
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] dm-snapshot: workaround for a lockdep warning
2013-09-18 15:57 ` Mikulas Patocka
@ 2013-09-18 19:07 ` Zdenek Kabelac
2013-09-18 23:14 ` Mikulas Patocka
0 siblings, 1 reply; 7+ messages in thread
From: Zdenek Kabelac @ 2013-09-18 19:07 UTC (permalink / raw)
To: Mikulas Patocka; +Cc: dm-devel, Stephen Boyd, Alasdair G. Kergon
Dne 18.9.2013 17:57, Mikulas Patocka napsal(a):
>
>
> On Wed, 18 Sep 2013, Zdenek Kabelac wrote:
>
>> Dne 18.9.2013 02:08, Mikulas Patocka napsal(a):
>>>
>>>
>>> On Tue, 17 Sep 2013, Mikulas Patocka wrote:
>>>
>>>> BTW. this patch is no longer needed on 3.11 because md->io_lock was
>>>> removed there, so the false lockdep warning doesn't happen.
>>>>
>>>> So we need to get this patch to stable trees 3.5 to 3.10, but not
>>>> upstream. How to push the patch there without pushing it upstream?
>>>>
>>>> Mikulas
>>>
>>> It's more complicated than that - the original Zdenek's report shows that
>>> the false warning happened on kernel "3.11.1-300.fc20.x86_64+debug". But I
>>> am not able to reproduce the bug on 3.11, I only reproduced it on 3.5-3.10
>>> kernels.
>>>
>>> Zdenek, could you reproduce the bug on kernel 3.11?
>>>
>>> Mikulas
>>>
>>
>>
>> Since I do not have clean 3.11 at my hands - I've reproduced it with my -rc6
>> kernel (few patches based on 8495e9c4a9616c9d19f23182d0536485902259db)
>> With enabled kmemleak=on lockdep.prove_locking=1 lockdep.lock_stat=1.
>
> So - try this patch and tell me if it fixes the problem:
>
> Index: linux-2.6-devel/drivers/md/dm-snap-persistent.c
> ===================================================================
> --- linux-2.6-devel.orig/drivers/md/dm-snap-persistent.c 2013-05-10 18:27:31.132358000 +0200
> +++ linux-2.6-devel/drivers/md/dm-snap-persistent.c 2013-09-17 18:41:39.023940000 +0200
> @@ -256,7 +256,7 @@
> */
> INIT_WORK_ONSTACK(&req.work, do_metadata);
> queue_work(ps->metadata_wq, &req.work);
> - flush_work(&req.work);
> + flush_workqueue(ps->metadata_wq);
>
> return req.result;
> }
>
Yes - this seems to eliminate reported INFO.
Though I'm getting curious why some tests are running much much much slower
when kmemleak and lockdep is in use.
Zdenek
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH] dm-snapshot: workaround for a lockdep warning
2013-09-18 19:07 ` Zdenek Kabelac
@ 2013-09-18 23:14 ` Mikulas Patocka
0 siblings, 0 replies; 7+ messages in thread
From: Mikulas Patocka @ 2013-09-18 23:14 UTC (permalink / raw)
To: dm-devel, Zdenek Kabelac; +Cc: Tejun Heo, Stephen Boyd, Alasdair G. Kergon
On Wed, 18 Sep 2013, Zdenek Kabelac wrote:
> Dne 18.9.2013 17:57, Mikulas Patocka napsal(a):
> >
> >
> > On Wed, 18 Sep 2013, Zdenek Kabelac wrote:
> >
> > > Dne 18.9.2013 02:08, Mikulas Patocka napsal(a):
> > > >
> > > > It's more complicated than that - the original Zdenek's report
> > > > shows that the false warning happened on kernel
> > > > "3.11.1-300.fc20.x86_64+debug". But I am not able to reproduce the
> > > > bug on 3.11, I only reproduced it on 3.5-3.10 kernels.
> > > >
> > > > Zdenek, could you reproduce the bug on kernel 3.11?
> > > >
> > > > Mikulas
> > > >
> > >
> > >
> > > Since I do not have clean 3.11 at my hands - I've reproduced it with my
> > > -rc6
> > > kernel (few patches based on 8495e9c4a9616c9d19f23182d0536485902259db)
> > > With enabled kmemleak=on lockdep.prove_locking=1 lockdep.lock_stat=1.
> >
> > So - try this patch and tell me if it fixes the problem:
> >
> > Index: linux-2.6-devel/drivers/md/dm-snap-persistent.c
> > ===================================================================
> > --- linux-2.6-devel.orig/drivers/md/dm-snap-persistent.c 2013-05-10
> > 18:27:31.132358000 +0200
> > +++ linux-2.6-devel/drivers/md/dm-snap-persistent.c 2013-09-17
> > 18:41:39.023940000 +0200
> > @@ -256,7 +256,7 @@
> > */
> > INIT_WORK_ONSTACK(&req.work, do_metadata);
> > queue_work(ps->metadata_wq, &req.work);
> > - flush_work(&req.work);
> > + flush_workqueue(ps->metadata_wq);
> >
> > return req.result;
> > }
> >
>
> Yes - this seems to eliminate reported INFO.
OK - so I am submitting the patch for the upstream kernel too.
> Though I'm getting curious why some tests are running much much much slower
> when kmemleak and lockdep is in use.
Because these checks slow things down - that's nothing unexpected.
> Zdenek
Mikulas
---
dm-snapshot: workaround for a lockdep warning
The kernel reports a lockdep warning if a snapshot is invalidated because
it runs out of space.
The lockdep warning was triggered by commit
0976dfc1d0cd80a4e9dfaf87bd8744612bde475a in the kernel 3.5.
The warning is false positive. The real cause for the warning is that the
lockdep engine treats different instances of md->lock as a single lock.
This patch is a workaround - we use flush_workqueue instead of flush_work.
This code path is not performance sensitive (it is called only on
initialization or invalidation), thus it doesn't matter that we flush the
whole workqueue.
The real fix for the problem would be to teach the lockdep engine to treat
different instances of md->lock as separate locks.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Alasdair G Kergon <agk@redhat.com>
Cc: stable@kernel.org # 3.5+
Index: linux-2.6-devel/drivers/md/dm-snap-persistent.c
===================================================================
--- linux-2.6-devel.orig/drivers/md/dm-snap-persistent.c 2013-05-10 18:27:31.132358000 +0200
+++ linux-2.6-devel/drivers/md/dm-snap-persistent.c 2013-09-17 18:41:39.023940000 +0200
@@ -256,7 +256,7 @@
*/
INIT_WORK_ONSTACK(&req.work, do_metadata);
queue_work(ps->metadata_wq, &req.work);
- flush_work(&req.work);
+ flush_workqueue(ps->metadata_wq);
return req.result;
}
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2013-09-18 23:14 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2013-09-17 20:47 [PATCH] dm-snapshot: workaround for a lockdep warning Mikulas Patocka
2013-09-17 23:24 ` Mikulas Patocka
2013-09-18 0:08 ` Mikulas Patocka
2013-09-18 6:57 ` Zdenek Kabelac
2013-09-18 15:57 ` Mikulas Patocka
2013-09-18 19:07 ` Zdenek Kabelac
2013-09-18 23:14 ` Mikulas Patocka
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