Messages in this thread | | | Date | Tue, 10 Dec 2013 10:40:33 -0800 | Subject | Re: process 'stuck' at exit. | From | Linus Torvalds <> |
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Hmm. Looks like the futex code is somehow stuck in a loop, calling get_user_pages_fast().
The futex code itself is apparently so low-overhead that it doesn't show up in your 'perf top' report (which is dominated by all the expensive debug things that get_user_pages_fast() etc ends up doing), but that's the only looping I can see. Perhaps the "goto again" case for transparent huge pages in get_futex_key()? Or the "retry[_private]" cases in futex_requeue()? Some error condition that causes us to retry forever, rather than returning the error code?
Added a few more people to the cc.. Ideas?
Linus
On Tue, Dec 10, 2013 at 7:47 AM, Dave Jones <davej@redhat.com> wrote: > I woke up to find my fuzzer in a curious state. > > 1121 pts/5 SN+ 0:00 | \_ ../trinity -q -l off -N 999999 -C 42 > 1130 pts/5 SN+ 0:01 | \_ ../trinity -q -l off -N 999999 -C 42 > 1131 pts/5 SN+ 0:17 | \_ ../trinity -q -l off -N 999999 -C 42 > 10818 ? RNs 21115152:53 | \_ ../trinity -q -l off -N 999999 -C 42 > > (ignore the first 3 pids, they're waiting on 10818, which is the interesting one) > > It's completed its run of 999999 syscalls, and looking at tmux, it tried to exit. > > /proc/10818/stack just shows > > [<ffffffffffffffff>] 0xffffffffffffffff > > Top reports a core is spinning in the kernel 100%, so I ran perf top -a > and saw.. > > 8.63% [kernel] [k] trace_hardirqs_off_caller > 7.68% [kernel] [k] __lock_acquire > 5.35% [kernel] [k] gup_huge_pmd > 5.31% [kernel] [k] put_compound_page > 4.93% [kernel] [k] gup_pud_range > 4.76% [kernel] [k] trace_hardirqs_on_caller > 4.58% [kernel] [k] get_user_pages_fast > 4.00% [kernel] [k] debug_smp_processor_id > 4.00% [kernel] [k] lock_is_held > 3.73% [kernel] [k] lock_acquired > 3.67% [kernel] [k] lock_release > > > sysrq-t shows.. > > trinity-child27 R running task 5520 10818 1131 0x00080004 > 0000000000000000 ffff8801b0ef4170 000000000000032c ffff8801b609e108 > 0000000000000000 ffff880160d21c30 ffffffff810ad895 ffffffff817587a0 > ffff8801b0ef4170 ffff8801b609e0a8 ffff8801b609e000 ffff880160d21d50 > Call Trace: > [<ffffffff817587a0>] ? retint_restore_args+0xe/0xe > [<ffffffff8132af0e>] ? trace_hardirqs_on_thunk+0x3a/0x3f > [<ffffffff8100b184>] ? native_sched_clock+0x24/0x80 > [<ffffffff8109624f>] ? local_clock+0xf/0x50 > [<ffffffff810aa27e>] ? put_lock_stats.isra.28+0xe/0x30 > [<ffffffff8103edd0>] ? gup_pud_range+0x170/0x190 > [<ffffffff8103f0d5>] ? get_user_pages_fast+0x1a5/0x1c0 > [<ffffffff810ad1f5>] ? trace_hardirqs_on_caller+0x115/0x1e0 > [<ffffffff810a8a2f>] ? up_read+0x1f/0x40 > [<ffffffff8103f0d5>] ? get_user_pages_fast+0x1a5/0x1c0 > [<ffffffff8115f76c>] ? put_page+0x3c/0x50 > [<ffffffff810dd525>] ? get_futex_key+0xd5/0x2c0 > [<ffffffff810df18a>] ? futex_requeue+0xfa/0x9c0 > [<ffffffff810e019e>] ? do_futex+0xae/0xc80 > [<ffffffff810aa27e>] ? put_lock_stats.isra.28+0xe/0x30 > [<ffffffff810aa7de>] ? lock_release_holdtime.part.29+0xee/0x170 > [<ffffffff8114f16e>] ? context_tracking_user_exit+0x4e/0x190 > [<ffffffff810ad1f5>] ? trace_hardirqs_on_caller+0x115/0x1e0 > [<ffffffff810e0de1>] ? SyS_futex+0x71/0x150 > [<ffffffff81010a45>] ? syscall_trace_enter+0x145/0x2a0 > [<ffffffff81760be4>] ? tracesys+0xdd/0xe2 > > > any ideas ? > > Dave >
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