Re: [PATCH] perf/x86/intel/bts: don't dereference ds unconditionally

From	Alexander Shishkin <alexander.shishkin@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] perf/x86/intel/bts: don't dereference ds unconditionally
Date	2016-09-20 15:50 +0200
Message-ID	<sjtAR-3Al-19@gated-at.bofh.it> (permalink)
References	<seoBP-2y1-9@gated-at.bofh.it> <seoLv-2B1-27@gated-at.bofh.it> <sjt7P-3qP-17@gated-at.bofh.it>
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Sebastian Andrzej Siewior <sebastian@breakpoint.cc> writes:

> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>
> Since commit 4d4c47412464 ("perf/x86/intel/bts: Fix BTS PMI detection")
> my box goes boom on boot:
>
> | .... node  #0, CPUs:      #1 #2 #3 #4 #5 #6 #7
> | BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
> | IP: [<ffffffff8100c463>] intel_bts_interrupt+0x43/0x130
> | Call Trace:
> |  <NMI> d [<ffffffff8100b341>] intel_pmu_handle_irq+0x51/0x4b0
> |  [<ffffffff81004d47>] perf_event_nmi_handler+0x27/0x40
>
> I don't know what is going on here but ds is not always dereferenced
> unconditionally hence here the `ds' check to avoid the crash.

Good catch! I'm going to guess you don't have the NMI watchdog enabled?

Thanks,
--
Alex

Thread

[PATCH] perf/x86/intel/bts: don't dereference ds unconditionally Sebastian Andrzej Siewior <sebastian@breakpoint.cc> - 2016-09-20 15:20 +0200
  Re: [PATCH] perf/x86/intel/bts: don't dereference ds unconditionally Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-20 15:50 +0200
    Re: [PATCH] perf/x86/intel/bts: don't dereference ds unconditionally Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-09-20 16:00 +0200
  [tip:perf/urgent] perf/x86/intel/bts: Make sure debug store is  valid tip-bot for Sebastian Andrzej Siewior <tipbot@zytor.com> - 2016-09-20 16:20 +0200

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