Re: rcu_preempt detected stalls.

[Dave Jones <davej@redhat.com>]

On Thu, Oct 23, 2014 at 11:32:32AM -0700, Paul E. McKenney wrote:
 
 > > trinity-c225    R  running task    13448   646  32295 0x00000000
 > >  ffff880161ccfb28 0000000000000002 ffff880161ccfe10 ffff88000bf85e00
 > >  00000000001d4100 0000000000000003 ffff880161ccffd8 00000000001d4100
 > >  ffff880030124680 ffff88000bf85e00 ffff880161ccffd8 0000000000000000
 > > Call Trace:
 > >  [<ffffffff888368e2>] preempt_schedule_irq+0x52/0xb0
 > >  [<ffffffff8883df10>] retint_kernel+0x20/0x30
 > >  [<ffffffff88233d41>] ? __d_lookup_rcu+0xd1/0x1e0
 > >  [<ffffffff88233dd6>] ? __d_lookup_rcu+0x166/0x1e0
 > >  [<ffffffff88222f9f>] lookup_fast+0x4f/0x3d0
 > >  [<ffffffff88224857>] link_path_walk+0x1a7/0x8a0
 > >  [<ffffffff88224f95>] ? path_lookupat+0x45/0x7b0
 > >  [<ffffffff88224fb7>] path_lookupat+0x67/0x7b0
 > >  [<ffffffff880d385d>] ? trace_hardirqs_off+0xd/0x10
 > >  [<ffffffff8883dda4>] ? retint_restore_args+0xe/0xe
 > >  [<ffffffff8822572b>] filename_lookup+0x2b/0xc0
 > >  [<ffffffff88229c77>] user_path_at_empty+0x67/0xc0
 > >  [<ffffffff880d3dbe>] ? put_lock_stats.isra.27+0xe/0x30
 > >  [<ffffffff880d42a6>] ? lock_release_holdtime.part.28+0xe6/0x160
 > >  [<ffffffff880b15ad>] ? get_parent_ip+0xd/0x50
 > >  [<ffffffff88229ce1>] user_path_at+0x11/0x20
 > >  [<ffffffff8824fac1>] do_utimes+0xd1/0x180
 > >  [<ffffffff8824fbef>] SyS_utime+0x7f/0xc0
 > >  [<ffffffff8883d345>] ? tracesys+0x7e/0xe2
 > >  [<ffffffff8883d3a4>] tracesys+0xdd/0xe2
 > 
 > This one will require more looking.  But did you do something like
 > create a pair of mutually recursive symlinks or something?  ;-)

I'm not 100% sure, but this may have been on a box that I was running
tests on NFS. So maybe the server had disappeared with the mount
still active..

Just a guess tbh.

	Dave