linux-kernel - Re: [PATCHv3] perf/x86/intel: Add cpu_(prepare|starting|dying) for core

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Message-ID: <20150421210016.GC2898@worktop.Skamania.guest>
Date:	Tue, 21 Apr 2015 23:00:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCHv3] perf/x86/intel: Add cpu_(prepare|starting|dying) for
 core_pmu

On Tue, Apr 21, 2015 at 05:26:23PM +0200, Jiri Olsa wrote:
> The core_pmu does not define cpu_* callbacks, which handles
> allocation of 'struct cpu_hw_events::shared_regs' data,
> initialization of debug store and PMU_FL_EXCL_CNTRS counters.
> 
> While this probably won't happen on bare metal, virtual CPU can
> define x86_pmu.extra_regs together with PMU version 1 and thus
> be using core_pmu -> using shared_regs data without it being
> allocated. That could could leave to following panic:
> 
> BUG: unable to handle kernel NULL pointer dereference at (null)
> IP: [<ffffffff8152cd4f>] _spin_lock_irqsave+0x1f/0x40
> 
> SNIP
> 
>  [<ffffffff81024bd9>] __intel_shared_reg_get_constraints+0x69/0x1e0
>  [<ffffffff81024deb>] intel_get_event_constraints+0x9b/0x180
>  [<ffffffff8101e815>] x86_schedule_events+0x75/0x1d0
>  [<ffffffff810586dc>] ? check_preempt_curr+0x7c/0x90
>  [<ffffffff810649fe>] ? try_to_wake_up+0x24e/0x3e0
>  [<ffffffff81064ba2>] ? default_wake_function+0x12/0x20
>  [<ffffffff8109eb16>] ? autoremove_wake_function+0x16/0x40
>  [<ffffffff810577e9>] ? __wake_up_common+0x59/0x90
>  [<ffffffff811a9517>] ? __d_lookup+0xa7/0x150
>  [<ffffffff8119db5f>] ? do_lookup+0x9f/0x230
>  [<ffffffff811a993a>] ? dput+0x9a/0x150
>  [<ffffffff8119c8f5>] ? path_to_nameidata+0x25/0x60
>  [<ffffffff8119e90a>] ? __link_path_walk+0x7da/0x1000
>  [<ffffffff8101d8f9>] ? x86_pmu_add+0xb9/0x170
>  [<ffffffff8101d7a7>] x86_pmu_commit_txn+0x67/0xc0
>  [<ffffffff811b07b0>] ? mntput_no_expire+0x30/0x110
>  [<ffffffff8119c731>] ? path_put+0x31/0x40
>  [<ffffffff8107c297>] ? current_fs_time+0x27/0x30
>  [<ffffffff8117d170>] ? mem_cgroup_get_reclaim_stat_from_page+0x20/0x70
>  [<ffffffff8111b7aa>] group_sched_in+0x13a/0x170
>  [<ffffffff81014a29>] ? sched_clock+0x9/0x10
>  [<ffffffff8111bac8>] ctx_sched_in+0x2e8/0x330
>  [<ffffffff8111bb7b>] perf_event_sched_in+0x6b/0xb0
>  [<ffffffff8111bc36>] perf_event_context_sched_in+0x76/0xc0
>  [<ffffffff8111eb3b>] perf_event_comm+0x1bb/0x2e0
>  [<ffffffff81195ee9>] set_task_comm+0x69/0x80
>  [<ffffffff81195fe1>] setup_new_exec+0xe1/0x2e0
>  [<ffffffff811ea68e>] load_elf_binary+0x3ce/0x1ab0
> 
> Adding cpu_(prepare|starting|dying) for core_pmu to have shared_regs
> data allocated for core_pmu. AFAICS there's no harm to initialize
> debug store and PMU_FL_EXCL_CNTRS either for core_pmu.
> 
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
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