linux-kernel - Re: [PATCH 1/2] hw_breakpoint: Fix cpu check in task_bp

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Date:	Thu, 13 Jun 2013 16:20:28 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	trinity@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 1/2] hw_breakpoint: Fix cpu check in task_bp_pinned(cpu)

On Sat, Jun 01, 2013 at 08:21:20PM +0200, Oleg Nesterov wrote:
> trinity fuzzer triggered WARN_ONCE("Can't find any breakpoint slot")
> in arch_install_hw_breakpoint() but the problem is not arch-specific.
> 
> The problem is, task_bp_pinned(cpu) checks "cpu == iter->cpu" but
> this doesn't account the "all cpus" events with iter->cpu < 0.
> 
> This means that, say, register_user_hw_breakpoint(tsk) can happily
> create the arbitrary number > HBP_NUM of breakpoints which can not
> be activated. toggle_bp_task_slot() is equally wrong by the same
> reason and nr_task_bp_pinned[] can have negative entries.
> 
> Simple test:
> 
> 	# perl -e 'sleep 1 while 1' &
> 	# perf record -e mem:0x10,mem:0x10,mem:0x10,mem:0x10,mem:0x10 -p `pidof perl`
> 
> Before this patch this triggers the same problem/WARN_ON(), after
> the patch it correctly fails with -ENOSPC.
> 
> Reported-by: Vince Weaver <vincent.weaver@...ne.edu>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Cc: <stable@...r.kernel.org>

Looks good, thanks!

Acked-by: Frederic Weisbecker <fweisbec@...il.com>


> ---
>  kernel/events/hw_breakpoint.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> index ed1c897..29d3abe 100644
> --- a/kernel/events/hw_breakpoint.c
> +++ b/kernel/events/hw_breakpoint.c
> @@ -120,7 +120,7 @@ static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
>  	list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
>  		if (iter->hw.bp_target == tsk &&
>  		    find_slot_idx(iter) == type &&
> -		    cpu == iter->cpu)
> +		    (iter->cpu < 0 || cpu == iter->cpu))
>  			count += hw_breakpoint_weight(iter);
>  	}
>  
> -- 
> 1.5.5.1
> 
> 
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