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Date: Tue, 15 Dec 2015 14:39:47 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@redhat.com>, Arnaldo Carvalho de Melo <acme@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Kostya Serebryany <kcc@google.com>,
        Alexander Potapenko <glider@google.com>,
        Sasha Levin <sasha.levin@oracle.com>,
        Eric Dumazet <edumazet@google.com>
Subject: Re: perf: stalls in perf_install_in_context/perf_remove_from_context
Message-ID: <20151215133947.GG6357@twins.programming.kicks-ass.net>
References: <CACT4Y+Za4L4q6FZLXjyGbnSYRwa7RJZYcG_s562q+CrNy9C75w@mail.gmail.com>
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On Tue, Dec 15, 2015 at 02:01:32PM +0100, Dmitry Vyukov wrote:


> Call Trace:
>  <IRQ>  [<ffffffff810e5e38>] sched_show_task+0x148/0x250 kernel/sched/core.c:4934

 <snip>

>  [<ffffffff823ff46c>] apic_timer_interrupt+0x8c/0xa0 arch/x86/entry/entry_64.S:520
>
>  <EOI>  [<     inline     >] ? arch_local_irq_enable ./arch/x86/include/asm/paravirt.h:816
>  <EOI>  [<     inline     >] ? __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:170
>  <EOI>  [<ffffffff823fde9e>] ? _raw_spin_unlock_irq+0x2e/0x40 kernel/locking/spinlock.c:199
>  [<     inline     >] ? __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:170
>  [<ffffffff823fde97>] ? _raw_spin_unlock_irq+0x27/0x40 kernel/locking/spinlock.c:199
>  [<ffffffff8119c8bb>] perf_install_in_context+0x6b/0xf0 kernel/events/core.c:2173
>  [<ffffffff811a492c>] SYSC_perf_event_open+0x63c/0xe40 kernel/events/core.c:8565
>  [<ffffffff811a7739>] SyS_perf_event_open+0x9/0x10 kernel/events/core.c:8261
>  [<ffffffff823fe676>] entry_SYSCALL_64_fastpath+0x16/0x7a arch/x86/entry/entry_64.S:185


So this looks like its stuck in the retry loop in
perf_install_in_context(). We do the raw_spin_unlock_irq(), which allows
the above watchdog interrupt to happen, but make no progress.

This means the task_function_call() thing keeps failing, which is
extremely unlikely.

Let me have a play with your test-case to see if it reproduces.