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Date: Tue, 6 Sep 2016 10:13:23 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: lkml <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Yanqiu Zhang <yanqzhan@redhat.com>, Tony Luck <tony.luck@intel.com>,
        Vikas Shivappa <vikas.shivappa@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] perf/x86/intel/cqm: Check cqm/mbm enabled state in event
 init
Message-ID: <20160906081323.GE10153@twins.programming.kicks-ass.net>
References: <1473089407-21857-1-git-send-email-jolsa@kernel.org>
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On Mon, Sep 05, 2016 at 05:30:07PM +0200, Jiri Olsa wrote:
> Yanqiu Zhang reported kernel panic when using mbm event
> on system where CQM is detected but without mbm event
> support, like with perf:
> 
>   # perf stat -e 'intel_cqm/event=3/' -a
> 
>   BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
>   IP: [<ffffffff8100d64c>] update_sample+0xbc/0xe0
>   ...
>    <IRQ>
>    [<ffffffff8100d688>] __intel_mbm_event_init+0x18/0x20
>    [<ffffffff81113d6b>] flush_smp_call_function_queue+0x7b/0x160
>    [<ffffffff81114853>] generic_smp_call_function_single_interrupt+0x13/0x60
>    [<ffffffff81052017>] smp_call_function_interrupt+0x27/0x40
>    [<ffffffff816fb06c>] call_function_interrupt+0x8c/0xa0
>   ...
> 
> The reason is that we currently allow to init mbm event
> even if mbm support is not detected.  Adding checks for
> both cqm and mbm events and support into cqm's event_init.
> 
> Reported-by: Yanqiu Zhang <yanqzhan@redhat.com>
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>

Fixes: 33c3cc7acfd9 ("perf/x86/mbm: Add Intel Memory B/W Monitoring enumeration and init")

Cc: stable@vger.kernelo.org # 4.6+