Messages in this thread | | | Date | Wed, 23 Apr 2014 11:11:53 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: 3.15rc2 hanging processes on exit. |
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On Wed, 23 Apr 2014, Linus Torvalds wrote: > On Wed, Apr 23, 2014 at 7:49 AM, Dave Jones <davej@redhat.com> wrote: > > > > So for reasons I can't figure out, I've not been able to hit it on 3.14
Thanks for trying. Not the reassuring answer that I was hoping for, so I'd better give it a little more thought, to see if we have some reason in 3.15-rc why it should now appear. Not worth spending too much effort on, though: Linus's fix looked good whatever.
> > The only 'interesting' thing I've hit in overnight testing is this, which > > I'm not sure if I've also seen in my .15rc testing, but it doesn't look > > familiar to me. (Though the vm oopses I've seen the last few months > > are starting to all blur together in my memory) > > > > > > kernel BUG at mm/mlock.c:82! > > That's > > mlock_vma_page: > BUG_ON(!PageLocked(page)); > > which is odd, because: > > > Call Trace: > > [<ffffffffbe196612>] try_to_unmap_nonlinear+0x2a2/0x530 > > [<ffffffffbe1972a7>] rmap_walk+0x157/0x320 > > [<ffffffffbe1976e3>] try_to_unmap+0x93/0xf0 > > [<ffffffffbe1bb8f6>] migrate_pages+0x3b6/0x7b0 > > All the calls to "try_to_unmap()" in mm/migrate.c are preceded by the pattern > > if (!trylock_page(page)) { > .... > lock_page(page); > }
Yes, that's true of the mm/migrate.c end, but the nonlinear try_to_unmap_cluster() (Being unable to point directly to the desired page) does this thing of unmapping a cluster of (likely unrelated) pages, in the hope that if it keeps getting called repeatedly, it will sooner or later have unmapped everything required.
> > where there are just a few "goto out" style cases for the "ok, we're > not going to wait for this page lock" in there. > > Very odd. Does anybody see anything I missed?
Easily explained (correct me if I'm wrong): Dave is reporting this from his testing of 3.14, but Linus is looking at his 3.15-rc git tree, which now contains
commit 57e68e9cd65b4b8eb4045a1e0d0746458502554c Author: Vlastimil Babka <vbabka@suse.cz> Date: Mon Apr 7 15:37:50 2014 -0700 mm: try_to_unmap_cluster() should lock_page() before mlocking
precisely to fix this (long-standing but long-unnoticed) issue, which Sasha reported a couple of months ago.
Hugh
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