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Message-ID: <20090416085153.GC9813@elte.hu>
Date: Thu, 16 Apr 2009 10:51:53 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: Alexander Beregalov <a.beregalov@...il.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
linux-nfs@...r.kernel.org, netdev@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>,
Alessio Igor Bogani <abogani@...ware.it>,
Jeff Mahoney <jeffm@...e.com>,
ReiserFS Development List <reiserfs-devel@...r.kernel.org>,
Chris Mason <chris.mason@...cle.com>
Subject: Re: [tree] latest kill-the-BKL tree, v12
* Frederic Weisbecker <fweisbec@...il.com> wrote:
> On Thu, Apr 16, 2009 at 01:07:36AM +0200, Ingo Molnar wrote:
> >
> > * Alexander Beregalov <a.beregalov@...il.com> wrote:
> >
> > > 2009/4/14 Ingo Molnar <mingo@...e.hu>:
> > > >
> > > > * Alexander Beregalov <a.beregalov@...il.com> wrote:
> > > >
> > > >> On Tue, Apr 14, 2009 at 05:34:22AM +0200, Frederic Weisbecker wrote:
> > > >> > Ingo,
> > > >> >
> > > >> > This small patchset fixes some deadlocks I've faced after trying
> > > >> > some pressures with dbench on a reiserfs partition.
> > > >> >
> > > >> > There is still some work pending such as adding some checks to ensure we
> > > >> > _always_ release the lock before sleeping, as you suggested.
> > > >> > Also I have to fix a lockdep warning reported by Alessio Igor Bogani.
> > > >> > And also some optimizations....
> > > >> >
> > > >> > Thanks,
> > > >> > Frederic.
> > > >> >
> > > >> > Frederic Weisbecker (3):
> > > >> > kill-the-BKL/reiserfs: provide a tool to lock only once the write lock
> > > >> > kill-the-BKL/reiserfs: lock only once in reiserfs_truncate_file
> > > >> > kill-the-BKL/reiserfs: only acquire the write lock once in
> > > >> > reiserfs_dirty_inode
> > > >> >
> > > >> > fs/reiserfs/inode.c | 10 +++++++---
> > > >> > fs/reiserfs/lock.c | 26 ++++++++++++++++++++++++++
> > > >> > fs/reiserfs/super.c | 15 +++++++++------
> > > >> > include/linux/reiserfs_fs.h | 2 ++
> > > >> > 4 files changed, 44 insertions(+), 9 deletions(-)
> > > >> >
> > > >>
> > > >> Hi
> > > >>
> > > >> The same test - dbench on reiserfs on loop on sparc64.
> > > >>
> > > >> [ INFO: possible circular locking dependency detected ]
> > > >> 2.6.30-rc1-00457-gb21597d-dirty #2
> > > >
> > > > I'm wondering ... your version hash suggests you used vanilla
> > > > upstream as a base for your test. There's a string of other fixes
> > > > from Frederic in tip:core/kill-the-BKL branch, have you picked them
> > > > all up when you did your testing?
> > > >
> > > > The most coherent way to test this would be to pick up the latest
> > > > core/kill-the-BKL git tree from:
> > > >
> > > > git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git core/kill-the-BKL
> > > >
> > >
> > > I did not know about this branch, now I am testing it and there is
> > > no more problem with that testcase (dbench).
> > >
> > > I will continue testing.
> >
> > thanks for testing it! It seems reiserfs with Frederic's changes
> > appears to be more stable now on your system.
>
>
>
>
> Yeah, thanks a lot for this testing!
>
>
>
> > I saw your NFS circular locking kill-the-BKL problem report on LKML
> > - also attached below.
> >
> > Hopefully someone on the Cc: list with NFS experience can point out
> > the BKL assumption that is causing this.
> >
> > Ingo
> >
> > ----- Forwarded message from Alexander Beregalov <a.beregalov@...il.com> -----
> >
> > Date: Wed, 15 Apr 2009 22:08:01 +0400
> > From: Alexander Beregalov <a.beregalov@...il.com>
> > To: linux-kernel <linux-kernel@...r.kernel.org>,
> > Ingo Molnar <mingo@...e.hu>, linux-nfs@...r.kernel.org
> > Subject: [core/kill-the-BKL] nfs3: possible circular locking dependency
> >
> > Hi
> >
> > I have pulled core/kill-the-BKL on top of 2.6.30-rc2.
> >
> > device: '0:18': device_add
> >
> > =======================================================
> > [ INFO: possible circular locking dependency detected ]
> > 2.6.30-rc2-00057-g30aa902-dirty #5
> > -------------------------------------------------------
> > mount.nfs/1740 is trying to acquire lock:
> > (kernel_mutex){+.+.+.}, at: [<00000000006f32dc>] lock_kernel+0x28/0x3c
> >
> > but task is already holding lock:
> > (&type->s_umount_key#24/1){+.+.+.}, at: [<00000000004b88a0>] sget+0x228/0x36c
> >
> > which lock already depends on the new lock.
> >
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #1 (&type->s_umount_key#24/1){+.+.+.}:
> > [<00000000004776d0>] lock_acquire+0x5c/0x74
> > [<0000000000469f5c>] down_write_nested+0x38/0x50
> > [<00000000004b88a0>] sget+0x228/0x36c
> > [<00000000005688fc>] nfs_get_sb+0x80c/0xa7c
> > [<00000000004b7ec8>] vfs_kern_mount+0x44/0xa4
> > [<00000000004b7f84>] do_kern_mount+0x30/0xcc
> > [<00000000004cf300>] do_mount+0x7c8/0x80c
> > [<00000000004ed2a4>] compat_sys_mount+0x224/0x274
> > [<0000000000406154>] linux_sparc_syscall32+0x34/0x40
> >
> > -> #0 (kernel_mutex){+.+.+.}:
> > [<00000000004776d0>] lock_acquire+0x5c/0x74
> > [<00000000006f0ebc>] mutex_lock_nested+0x48/0x380
> > [<00000000006f32dc>] lock_kernel+0x28/0x3c
> > [<00000000006d20ec>] rpc_wait_bit_killable+0x64/0x8c
> > [<00000000006f0620>] __wait_on_bit+0x64/0xc0
> > [<00000000006f06e4>] out_of_line_wait_on_bit+0x68/0x7c
> > [<00000000006d2938>] __rpc_execute+0x150/0x2b4
> > [<00000000006d2ac0>] rpc_execute+0x24/0x34
> > [<00000000006cc338>] rpc_run_task+0x64/0x74
> > [<00000000006cc474>] rpc_call_sync+0x58/0x7c
> > [<00000000005717b0>] nfs3_rpc_wrapper+0x24/0xa0
> > [<0000000000572024>] do_proc_get_root+0x6c/0x10c
> > [<00000000005720dc>] nfs3_proc_get_root+0x18/0x5c
> > [<000000000056401c>] nfs_get_root+0x34/0x17c
> > [<0000000000568adc>] nfs_get_sb+0x9ec/0xa7c
> > [<00000000004b7ec8>] vfs_kern_mount+0x44/0xa4
> > [<00000000004b7f84>] do_kern_mount+0x30/0xcc
> > [<00000000004cf300>] do_mount+0x7c8/0x80c
> > [<00000000004ed2a4>] compat_sys_mount+0x224/0x274
> > [<0000000000406154>] linux_sparc_syscall32+0x34/0x40
>
>
>
>
> This is still the dependency between bkl and s_umount_key that has
> been reported recently. I wonder if this is not a problem in the
> fs layer. I should investigate on it.
The problem seem to be that this NFS call context:
-> #0 (kernel_mutex){+.+.+.}:
[<00000000004776d0>] lock_acquire+0x5c/0x74
[<00000000006f0ebc>] mutex_lock_nested+0x48/0x380
[<00000000006f32dc>] lock_kernel+0x28/0x3c
[<00000000006d20ec>] rpc_wait_bit_killable+0x64/0x8c
[<00000000006f0620>] __wait_on_bit+0x64/0xc0
[<00000000006f06e4>] out_of_line_wait_on_bit+0x68/0x7c
[<00000000006d2938>] __rpc_execute+0x150/0x2b4
[<00000000006d2ac0>] rpc_execute+0x24/0x34
[<00000000006cc338>] rpc_run_task+0x64/0x74
[<00000000006cc474>] rpc_call_sync+0x58/0x7c
[<00000000005717b0>] nfs3_rpc_wrapper+0x24/0xa0
[<0000000000572024>] do_proc_get_root+0x6c/0x10c
[<00000000005720dc>] nfs3_proc_get_root+0x18/0x5c
[<000000000056401c>] nfs_get_root+0x34/0x17c
[<0000000000568adc>] nfs_get_sb+0x9ec/0xa7c
[<00000000004b7ec8>] vfs_kern_mount+0x44/0xa4
[<00000000004b7f84>] do_kern_mount+0x30/0xcc
[<00000000004cf300>] do_mount+0x7c8/0x80c
[<00000000004ed2a4>] compat_sys_mount+0x224/0x274
[<0000000000406154>] linux_sparc_syscall32+0x34/0x40
Can be called with the BKL held - and then it schedule()s with the
BKL held, creating dependencies. I did the quick hack below (a year
ago! :-) but indeed that's probably wrong: we just drop and then
re-acquire the BKL at a very low level - inverting the dependency
chain.
It's not a problem of the NFS code, it's the probem of
vfs_kern_mount taking the BKL.
Maybe it would be better if nfs_get_sb() dropped the BKL (knowing
that it's called with the BKL held) - since it does not rely on the
BKL? Not rpc_wait_bit_killable().
Ingo
-------------->
>From 352e0d25def53e6b36234e4dc2083ca7f5d712a9 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@...e.hu>
Date: Wed, 14 May 2008 17:31:41 +0200
Subject: [PATCH] remove the BKL: restructure NFS code
the naked schedule() in rpc_wait_bit_killable() caused the BKL to
be auto-dropped in the past.
avoid the immediate hang in such code. Note that this still leaves
some other locking dependencies to be sorted out in the NFS code.
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
net/sunrpc/sched.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 6eab9bf..e12e571 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -224,9 +224,15 @@ EXPORT_SYMBOL_GPL(rpc_destroy_wait_queue);
static int rpc_wait_bit_killable(void *word)
{
+ int bkl = kernel_locked();
+
if (fatal_signal_pending(current))
return -ERESTARTSYS;
+ if (bkl)
+ unlock_kernel();
schedule();
+ if (bkl)
+ lock_kernel();
return 0;
}
--
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