linux-kernel - Re: [PATCH] perf: Fix oops when kthread execs user process

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Message-ID: <20190530103536.GA56046@lakrids.cambridge.arm.com>
Date:   Thu, 30 May 2019 11:35:36 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will.deacon@....com>,
        Young Xiao <92siuyang@...il.com>, linux@...linux.org.uk,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, x86@...nel.org,
        kan.liang@...ux.intel.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, ravi.bangoria@...ux.vnet.ibm.com,
        mpe@...erman.id.au, acme@...hat.com, eranian@...gle.com,
        fweisbec@...il.com, jolsa@...hat.com
Subject: Re: [PATCH] perf: Fix oops when kthread execs user process

On Wed, May 29, 2019 at 07:03:13PM +0200, Peter Zijlstra wrote:
> On Wed, May 29, 2019 at 05:38:54PM +0100, Mark Rutland wrote:
> > Generally speaking though, if we ever task task_pt_regs() of an idle
> > task we'll get junk, and user_mode() could be true.
> 
> Agreed, but we're not doing that.

Sure.

I just think that might be an argument for having task_pt_regs() return
NULL for kthreads, or having a WARN_ON_ONCE(t->flags & PF_KTHREAD) to
catch missing checks elsewhere.

Thanks,
Mark.