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Date:   Wed, 29 May 2019 15:25:15 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Will Deacon <will.deacon@arm.com>
Cc:     Young Xiao <92siuyang@gmail.com>, linux@armlinux.org.uk,
        mark.rutland@arm.com, mingo@redhat.com, bp@alien8.de,
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        ravi.bangoria@linux.vnet.ibm.com, mpe@ellerman.id.au,
        acme@redhat.com, eranian@google.com, fweisbec@gmail.com,
        jolsa@redhat.com
Subject: Re: [PATCH] perf: Fix oops when kthread execs user process
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On Wed, May 29, 2019 at 02:05:21PM +0100, Will Deacon wrote:
> On Wed, May 29, 2019 at 02:55:57PM +0200, Peter Zijlstra wrote:

> >  	if (user_mode(regs)) {
> 
> Hmm, so it just occurred to me that Mark's observation is that the regs
> can be junk in some cases. In which case, should we be checking for
> kthreads first?

task_pt_regs() can return garbage, but @regs is the exception (or
perf_arch_fetch_caller_regs()) regs, and for those user_mode() had
better be correct.