(Adding Greg to cc to see if he recalls seeing issues with sysfs dentry
suffering from recursive locking recently)
On Thu, Jan 05, 2012 at 10:35:04AM -0800, Paul E. McKenney wrote:
> On Thu, Jan 05, 2012 at 04:35:29PM +0000, Russell King - ARM Linux wrote:
> > On Thu, Jan 05, 2012 at 04:17:39PM +0000, Mel Gorman wrote:
> > > Link please?
> >
> > Forwarded, as its still in my mailbox.
> >
> > > I'm including a patch below under development that is
> > > intended to only cope with the page allocator case under heavy memory
> > > pressure. Currently it does not pass testing because eventually RCU
> > > gets stalled with the following trace
> > >
> > > [ 1817.176001] [<ffffffff810214d7>] arch_trigger_all_cpu_backtrace+0x87/0xa0
> > > [ 1817.176001] [<ffffffff810c4779>] __rcu_pending+0x149/0x260
> > > [ 1817.176001] [<ffffffff810c48ef>] rcu_check_callbacks+0x5f/0x110
> > > [ 1817.176001] [<ffffffff81068d7f>] update_process_times+0x3f/0x80
> > > [ 1817.176001] [<ffffffff8108c4eb>] tick_sched_timer+0x5b/0xc0
> > > [ 1817.176001] [<ffffffff8107f28e>] __run_hrtimer+0xbe/0x1a0
> > > [ 1817.176001] [<ffffffff8107f581>] hrtimer_interrupt+0xc1/0x1e0
> > > [ 1817.176001] [<ffffffff81020ef3>] smp_apic_timer_interrupt+0x63/0xa0
> > > [ 1817.176001] [<ffffffff81449073>] apic_timer_interrupt+0x13/0x20
> > > [ 1817.176001] [<ffffffff8116c135>] vfsmount_lock_local_lock+0x25/0x30
> > > [ 1817.176001] [<ffffffff8115c855>] path_init+0x2d5/0x370
> > > [ 1817.176001] [<ffffffff8115eecd>] path_lookupat+0x2d/0x620
> > > [ 1817.176001] [<ffffffff8115f4ef>] do_path_lookup+0x2f/0xd0
> > > [ 1817.176001] [<ffffffff811602af>] user_path_at_empty+0x9f/0xd0
> > > [ 1817.176001] [<ffffffff81154e7b>] vfs_fstatat+0x4b/0x90
> > > [ 1817.176001] [<ffffffff81154f4f>] sys_newlstat+0x1f/0x50
> > > [ 1817.176001] [<ffffffff81448692>] system_call_fastpath+0x16/0x1b
> > >
> > > It might be a separate bug, don't know for sure.
>
I rebased the patch on top of 3.2 and tested again with a bunch of
debugging options set (PROVE_RCU, PROVE_LOCKING etc). Same results. CPU
hotplug is a lot more reliable and less likely to hang but eventually
gets into trouble.
Taking a closer look though, I don't think this is an RCU problem. It's
just the messenger.
> Do you get multiple RCU CPU stall-warning messages?
Yes, one roughly every 50000 jiffies or so (HZ=250).
[ 878.315029] INFO: rcu_sched detected stall on CPU 3 (t=16250 jiffies)
[ 878.315032] INFO: rcu_sched detected stall on CPU 6 (t=16250 jiffies)
[ 1072.878669] INFO: rcu_sched detected stall on CPU 3 (t=65030 jiffies)
[ 1072.878672] INFO: rcu_sched detected stall on CPU 6 (t=65030 jiffies)
[ 1267.442308] INFO: rcu_sched detected stall on CPU 3 (t=113810 jiffies)
[ 1267.442312] INFO: rcu_sched detected stall on CPU 6 (t=113810 jiffies)
[ 1462.005948] INFO: rcu_sched detected stall on CPU 3 (t=162590 jiffies)
[ 1462.005952] INFO: rcu_sched detected stall on CPU 6 (t=162590 jiffies)
[ 1656.569588] INFO: rcu_sched detected stall on CPU 3 (t=211370 jiffies)
[ 1656.569592] INFO: rcu_sched detected stall on CPU 6 (t=211370 jiffies)
[ 1851.133229] INFO: rcu_sched detected stall on CPU 6 (t=260150 jiffies)
[ 1851.133233] INFO: rcu_sched detected stall on CPU 3 (t=260150 jiffies)
[ 2045.696868] INFO: rcu_sched detected stall on CPU 3 (t=308930 jiffies)
[ 2045.696872] INFO: rcu_sched detected stall on CPU 6 (t=308930 jiffies)
[ 2240.260508] INFO: rcu_sched detected stall on CPU 6 (t=357710 jiffies)
[ 2240.260511] INFO: rcu_sched detected stall on CPU 3 (t=357710 jiffies)
> If so, it can
> be helpful to look at how the stack frame changes over time. These
> stalls are normally caused by a loop in the kernel with preemption
> disabled, though other scenarios can also cause them.
>
The stacks are not changing much over time and start with this;
[ 878.315029] INFO: rcu_sched detected stall on CPU 3 (t=16250 jiffies)
[ 878.315032] INFO: rcu_sched detected stall on CPU 6 (t=16250 jiffies)
[ 878.315036] Pid: 4422, comm: udevd Not tainted 3.2.0-guardipi-v1r6 #2
[ 878.315037] Call Trace:
[ 878.315038] <IRQ> [<ffffffff810a8b20>] __rcu_pending+0x8e/0x36c
[ 878.315052] [<ffffffff81071b9a>] ? tick_nohz_handler+0xdc/0xdc
[ 878.315054] [<ffffffff810a8f04>] rcu_check_callbacks+0x106/0x172
[ 878.315056] [<ffffffff810528e0>] update_process_times+0x3f/0x76
[ 878.315058] [<ffffffff81071c0a>] tick_sched_timer+0x70/0x9a
[ 878.315060] [<ffffffff8106654e>] __run_hrtimer+0xc7/0x157
[ 878.315062] [<ffffffff810667ec>] hrtimer_interrupt+0xba/0x18a
[ 878.315065] [<ffffffff8134fbad>] smp_apic_timer_interrupt+0x86/0x99
[ 878.315067] [<ffffffff8134dbf3>] apic_timer_interrupt+0x73/0x80
[ 878.315068] <EOI> [<ffffffff81345f34>] ? retint_restore_args+0x13/0x13
[ 878.315072] [<ffffffff81139591>] ? __shrink_dcache_sb+0x7d/0x19f
[ 878.315075] [<ffffffff81008c6e>] ? native_read_tsc+0x1/0x16
[ 878.315077] [<ffffffff811df434>] ? delay_tsc+0x3a/0x82
[ 878.315079] [<ffffffff811df4a1>] __delay+0xf/0x11
[ 878.315081] [<ffffffff811e51e5>] do_raw_spin_lock+0xb5/0xf9
[ 878.315083] [<ffffffff81345561>] _raw_spin_lock+0x39/0x3d
[ 878.315085] [<ffffffff8113972a>] ? shrink_dcache_parent+0x77/0x28c
[ 878.315087] [<ffffffff8113972a>] shrink_dcache_parent+0x77/0x28c
[ 878.315089] [<ffffffff8113741d>] ? have_submounts+0x13e/0x1bd
[ 878.315092] [<ffffffff81185970>] sysfs_dentry_revalidate+0xaa/0xbe
[ 878.315093] [<ffffffff8112e731>] do_lookup+0x263/0x2fc
[ 878.315096] [<ffffffff8119ca13>] ? security_inode_permission+0x1e/0x20
[ 878.315098] [<ffffffff8112f33d>] link_path_walk+0x1e2/0x763
[ 878.315099] [<ffffffff8112fd66>] path_lookupat+0x5c/0x61a
[ 878.315102] [<ffffffff810f4810>] ? might_fault+0x89/0x8d
[ 878.315104] [<ffffffff810f47c7>] ? might_fault+0x40/0x8d
[ 878.315105] [<ffffffff8113034e>] do_path_lookup+0x2a/0xa8
[ 878.315107] [<ffffffff81132a51>] user_path_at_empty+0x5d/0x97
[ 878.315109] [<ffffffff8107447f>] ? trace_hardirqs_off+0xd/0xf
[ 878.315111] [<ffffffff81345c4f>] ? _raw_spin_unlock_irqrestore+0x44/0x5a
[ 878.315112] [<ffffffff81132a9c>] user_path_at+0x11/0x13
[ 878.315115] [<ffffffff81128b64>] vfs_fstatat+0x44/0x71
[ 878.315117] [<ffffffff81128bef>] vfs_lstat+0x1e/0x20
[ 878.315118] [<ffffffff81128c10>] sys_newlstat+0x1f/0x40
[ 878.315120] [<ffffffff810759a8>] ? trace_hardirqs_on_caller+0x12d/0x164
[ 878.315122] [<ffffffff811e057e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[ 878.315124] [<ffffffff8107447f>] ? trace_hardirqs_off+0xd/0xf
[ 878.315126] [<ffffffff8134d082>] system_call_fastpath+0x16/0x1b
[ 878.557790] Pid: 5704, comm: udevd Not tainted 3.2.0-guardipi-v1r6 #2
[ 878.564226] Call Trace:
[ 878.566677] <IRQ> [<ffffffff810a8b20>] __rcu_pending+0x8e/0x36c
[ 878.572783] [<ffffffff81071b9a>] ? tick_nohz_handler+0xdc/0xdc
[ 878.578702] [<ffffffff810a8f04>] rcu_check_callbacks+0x106/0x172
[ 878.584794] [<ffffffff810528e0>] update_process_times+0x3f/0x76
[ 878.590798] [<ffffffff81071c0a>] tick_sched_timer+0x70/0x9a
[ 878.596459] [<ffffffff8106654e>] __run_hrtimer+0xc7/0x157
[ 878.601944] [<ffffffff810667ec>] hrtimer_interrupt+0xba/0x18a
[ 878.607778] [<ffffffff8134fbad>] smp_apic_timer_interrupt+0x86/0x99
[ 878.614129] [<ffffffff8134dbf3>] apic_timer_interrupt+0x73/0x80
[ 878.620134] <EOI> [<ffffffff81051e66>] ? run_timer_softirq+0x49/0x32a
[ 878.626759] [<ffffffff81139591>] ? __shrink_dcache_sb+0x7d/0x19f
[ 878.632851] [<ffffffff811df402>] ? delay_tsc+0x8/0x82
[ 878.637988] [<ffffffff811df4a1>] __delay+0xf/0x11
[ 878.642778] [<ffffffff811e51e5>] do_raw_spin_lock+0xb5/0xf9
[ 878.648437] [<ffffffff81345561>] _raw_spin_lock+0x39/0x3d
[ 878.653920] [<ffffffff8113972a>] ? shrink_dcache_parent+0x77/0x28c
[ 878.660186] [<ffffffff8113972a>] shrink_dcache_parent+0x77/0x28c
[ 878.666277] [<ffffffff8113741d>] ? have_submounts+0x13e/0x1bd
[ 878.672107] [<ffffffff81185970>] sysfs_dentry_revalidate+0xaa/0xbe
[ 878.678372] [<ffffffff8112e731>] do_lookup+0x263/0x2fc
[ 878.683596] [<ffffffff8119ca13>] ? security_inode_permission+0x1e/0x20
[ 878.690207] [<ffffffff8112f33d>] link_path_walk+0x1e2/0x763
[ 878.695866] [<ffffffff8112fd66>] path_lookupat+0x5c/0x61a
[ 878.701350] [<ffffffff810f4810>] ? might_fault+0x89/0x8d
[ 878.706747] [<ffffffff810f47c7>] ? might_fault+0x40/0x8d
[ 878.712145] [<ffffffff8113034e>] do_path_lookup+0x2a/0xa8
[ 878.717630] [<ffffffff81132a51>] user_path_at_empty+0x5d/0x97
[ 878.723463] [<ffffffff8107447f>] ? trace_hardirqs_off+0xd/0xf
[ 878.729295] [<ffffffff81345c4f>] ? _raw_spin_unlock_irqrestore+0x44/0x5a
[ 878.736080] [<ffffffff81132a9c>] user_path_at+0x11/0x13
[ 878.741391] [<ffffffff81128b64>] vfs_fstatat+0x44/0x71
[ 878.746616] [<ffffffff81128bef>] vfs_lstat+0x1e/0x20
[ 878.751668] [<ffffffff81128c10>] sys_newlstat+0x1f/0x40
[ 878.756981] [<ffffffff810759a8>] ? trace_hardirqs_on_caller+0x12d/0x164
[ 878.763678] [<ffffffff811e057e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[ 878.770116] [<ffffffff8107447f>] ? trace_hardirqs_off+0xd/0xf
[ 878.775949] [<ffffffff8134d082>] system_call_fastpath+0x16/0x1b
[ 908.769486] BUG: spinlock lockup on CPU#6, udevd/4422
[ 908.774547] lock: ffff8803b4c701c8, .magic: dead4ead, .owner: udevd/5709, .owner_cpu: 4
Seeing that the owner was CPU 4, I found earlier in the log
[ 815.244051] BUG: spinlock lockup on CPU#4, udevd/5709
[ 815.249103] lock: ffff8803b4c701c8, .magic: dead4ead, .owner: udevd/5709, .owner_cpu: 4
[ 815.258430] Pid: 5709, comm: udevd Not tainted 3.2.0-guardipi-v1r6 #2
[ 815.264866] Call Trace:
[ 815.267329] [<ffffffff811e507d>] spin_dump+0x88/0x8d
[ 815.272388] [<ffffffff811e5206>] do_raw_spin_lock+0xd6/0xf9
[ 815.278062] [<ffffffff81345561>] ? _raw_spin_lock+0x39/0x3d
[ 815.283720] [<ffffffff8113972a>] ? shrink_dcache_parent+0x77/0x28c
[ 815.289986] [<ffffffff8113972a>] ? shrink_dcache_parent+0x77/0x28c
[ 815.296249] [<ffffffff8113741d>] ? have_submounts+0x13e/0x1bd
[ 815.302080] [<ffffffff81185970>] ? sysfs_dentry_revalidate+0xaa/0xbe
[ 815.308515] [<ffffffff8112e731>] ? do_lookup+0x263/0x2fc
[ 815.313915] [<ffffffff8119ca13>] ? security_inode_permission+0x1e/0x20
[ 815.320524] [<ffffffff8112f33d>] ? link_path_walk+0x1e2/0x763
[ 815.326357] [<ffffffff8112fd66>] ? path_lookupat+0x5c/0x61a
[ 815.332014] [<ffffffff810f4810>] ? might_fault+0x89/0x8d
[ 815.337410] [<ffffffff810f47c7>] ? might_fault+0x40/0x8d
[ 815.342807] [<ffffffff8113034e>] ? do_path_lookup+0x2a/0xa8
[ 815.348465] [<ffffffff81132a51>] ? user_path_at_empty+0x5d/0x97
[ 815.354474] [<ffffffff8107447f>] ? trace_hardirqs_off+0xd/0xf
[ 815.360303] [<ffffffff81345c4f>] ? _raw_spin_unlock_irqrestore+0x44/0x5a
[ 815.367085] [<ffffffff81132a9c>] ? user_path_at+0x11/0x13
[ 815.372569] [<ffffffff81128b64>] ? vfs_fstatat+0x44/0x71
[ 815.377965] [<ffffffff81128bef>] ? vfs_lstat+0x1e/0x20
[ 815.383192] [<ffffffff81128c10>] ? sys_newlstat+0x1f/0x40
[ 815.388676] [<ffffffff810759a8>] ? trace_hardirqs_on_caller+0x12d/0x164
[ 815.395373] [<ffffffff811e057e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[ 815.401811] [<ffffffff8107447f>] ? trace_hardirqs_off+0xd/0xf
[ 815.407642] [<ffffffff8134d082>] ? system_call_fastpath+0x16/0x1b
The trace is not particularly useful but it looks like it
recursively locked even though the message doesn't say that. If the
shrink_dcache_parent() entry is accurate, that corresponds to this
static int select_parent(struct dentry * parent)
{
struct dentry *this_parent;
struct list_head *next;
unsigned seq;
int found = 0;
int locked = 0;
seq = read_seqbegin(&rename_lock);
again:
this_parent = parent;
spin_lock(&this_parent->d_lock); <----- HERE
I'm not overly clear on how VFS locking is meant to work but it almost
looks as if the last reference to an inode is being dropped during a
sysfs path lookup. Is that meant to happen?
Judging by sysfs_dentry_revalidate() - possibly not. It looks like
we must have reached out_bad: and called shrink_dcache_parent() on a
dentry that was already locked by the running process. Not sure how
this could have happened - Greg, does this look familiar?
--
Mel Gorman
SUSE Labs
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