linux-kernel - Re: [perf] more perf_fuzzer memory corruption

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Message-ID: <20140501131245.GQ11096@twins.programming.kicks-ass.net>
Date:	Thu, 1 May 2014 15:12:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [perf] more perf_fuzzer memory corruption

On Thu, May 01, 2014 at 02:35:02PM +0200, Thomas Gleixner wrote:
> > grep ptr=0xffff880118fda000 bug.out | less
> > 
> > We find lovely bits such as:
> > 
> >      perf_fuzzer-4387  [001]  1773.427175: kmalloc:              (perf_event_alloc+0x5a) call_site=ffffffff8113a8fa ptr=0xffff880118fda000 bytes_req=1272 bytes_alloc=2048 gfp_flags=GFP_KERNEL|GFP_ZERO
> >      ksoftirqd/6-38    [006]  1773.457770: kfree:                (free_event_rcu+0x2f) call_site=ffffffff8113177f ptr=0xffff880118fda000
> >           <idle>-0     [007]  1774.020378: kfree:                (free_event_rcu+0x2f) call_site=ffffffff8113177f ptr=0xffff880118fda000
> >      perf_fuzzer-4387  [000]  1774.096354: kmalloc:              (perf_event_alloc+0x5a) call_site=ffffffff8113a8fa ptr=0xffff880118fda000 bytes_req=1272 bytes_alloc=2048 gfp_flags=GFP_KERNEL|GFP_ZERO
> > 
> > 
> > That's almost half a second between the double free, Vince, is your TSC
> > solid?
> 
> grep DROPPED bug.out
> 
> Now align that with the double malloc/free sites and you have an explanation ...

Argh!
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