Messages in this thread | | | Subject | Re: rcu: endless stalls | From | Mike Galbraith <> | Date | Wed, 13 Jun 2012 07:56:14 +0200 |
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On Tue, 2012-06-12 at 21:31 -0700, Hugh Dickins wrote: > On Wed, 13 Jun 2012, Mike Galbraith wrote: > > On Mon, 2012-06-11 at 20:10 +0200, Mike Galbraith wrote: > > > On Mon, 2012-06-11 at 11:01 -0700, Paul E. McKenney wrote: > > > > > > > 2aa15890 - mm: prevent concurrent unmap_mapping_range() on the same inode > > > > > > > > I confess, you lost me on this one. You believe that this commit is > > > > the cause of the RCU CPU stall warnings? > > > > > > 4096 tasks on 4096 CPUs exit (well, try to) simultaneously. > > > > > > Call Trace: > > > __mutex_lock_slowpath+0x94/0x150 > > > mutex_lock+0x1a/0x40 > > > unlink_file_vma+0x3f/0xf0 > > > free_pgtables+0x40/0x100 > > > exit_mmap+0xb0/0x120 > > > mmput+0x49/0x120 > > > exit_mm+0x122/0x160 > > > do_exit+0x179/0x8d0 > > > do_group_exit+0x3d/0xb0 > > > sys_exit_group+0x12/0x20 > > > > > > Monster box dies screaming. > > > > That commit landed in stable, box with way too many cores (NR_CPUS=0!!) > > chokes instantly with loads of spinners. Ok, so zillion CPUs grabbing a > > mutex in lockstep is a bad idea (_having_ zillion?), but is there pilot > > error involved in a logjam like this? > > Surely some mistake...
Yup.
> I can't find any mention of which kernel release you're talking about. > > But Miklos's 2aa15890 unmap_mutex was introduced in 2.6.38 and removed > in 3.0, when PeterZ converted i_mmap_lock to i_mmap_mutex, and removed > the need for the additional unmap_mutex. > > The unmap_mutex would never have been taken in unlink_file_vma(), > shown in your stacktrace above: it was for truncation and invalidation. > > The likely mutex in unlink_file_vma() would be the i_mmap_mutex. > So I expect you're talking about a 3.0 or later kernel.
Yeah.
> But then why would someone "backport" Miklos's patch to stable for it? > > You lost me too!
Sorry, /me is hopping around vigorously between too many darn trees, it's already there, not a stable addition.
Question remains though. Maybe the box hit some other problem that led to death by RCU gripage, but the info I received indicated the box was in the midst of a major spin-fest.
-Mike
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