linux-kernel - Re: events: possible deadlock in __perf_event_task_sched

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Date:   Mon, 21 Aug 2017 09:32:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Shubham Bansal <illusionist.neo@...il.com>
Cc:     mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com,
        LKML <linux-kernel@...r.kernel.org>, syzkaller@...glegroups.com
Subject: Re: events: possible deadlock in __perf_event_task_sched_out

On Mon, Aug 21, 2017 at 01:56:27AM +0530, Shubham Bansal wrote:
> -> #1 ((console_sem).lock){......}:
>        lock_acquire+0x173/0x470
>        _raw_spin_lock_irqsave+0x42/0x60
>        down_trylock+0x13/0x70
>        __down_trylock_console_sem+0x38/0xc0
>        console_trylock+0x17/0xb0
>        vprintk_emit+0x410/0x480
>        vprintk_default+0x28/0x30
>        vprintk_func+0x57/0xbe
>        printk+0x9f/0xbb
>        ex_handler_wrmsr_unsafe.cold.1+0xca/0xe2
>        fixup_exception+0x8b/0xb3
>        do_general_protection+0x18f/0x2b0
>        general_protection+0x28/0x30
>        native_write_msr+0x4/0x30
>        x86_pmu_enable+0x347/0xab0
>        ctx_resched+0x1e6/0x2b0
>        __perf_install_in_context+0x244/0x2c0
>        remote_function+0x8e/0x190
>        generic_exec_single+0x292/0x410
>        smp_call_function_single+0x339/0x510
>        task_function_call+0x162/0x220
>        perf_install_in_context+0x247/0x460
>        SYSC_perf_event_open+0x207c/0x2ea0
>        SyS_perf_event_open+0x39/0x50
>        entry_SYSCALL_64_fastpath+0x1f/0xbe

This is a WARN, printk is a pig.