| Message ID | 20090416085153.GC9813@elte.hu |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
Dear Sir Molnar, 2009/4/16 Ingo Molnar <mingo@elte.hu>: [...] >> 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 Proposed patch that i just sent (http://marc.info/?l=linux-kernel&m=123989213917572&w=2) seems fix the lock dependency. I don't know if it is the right way to solve the problem in any case but it works on my laptop, at least. Ciao, Alessio -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Apr 16, 2009 at 10:51:53AM +0200, Ingo Molnar wrote: > > * Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > On Thu, Apr 16, 2009 at 01:07:36AM +0200, Ingo Molnar wrote: > > > > > > * Alexander Beregalov <a.beregalov@gmail.com> wrote: > > > > > > > 2009/4/14 Ingo Molnar <mingo@elte.hu>: > > > > > > > > > > * Alexander Beregalov <a.beregalov@gmail.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@gmail.com> ----- > > > > > > Date: Wed, 15 Apr 2009 22:08:01 +0400 > > > From: Alexander Beregalov <a.beregalov@gmail.com> > > > To: linux-kernel <linux-kernel@vger.kernel.org>, > > > Ingo Molnar <mingo@elte.hu>, linux-nfs@vger.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. Indeed, the problem remains if we do that :-) > It's not a problem of the NFS code, it's the probem of > vfs_kern_mount taking the BKL. Yes, and I think the idea of Alessio to remove the Bkl at this level is the right way. Even though this patch is beeing discussed, I think it opened the right direction to dig. > 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(). I wonder if it is not dropped because it implicitly protects something else. May be simply concurrent accesses to the superblock? Frederic. > Ingo > > --------------> > From 352e0d25def53e6b36234e4dc2083ca7f5d712a9 Mon Sep 17 00:00:00 2001 > From: Ingo Molnar <mingo@elte.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@elte.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(); Yeah as you said, it may not drop but invert the dependency. > return 0; > } > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; }