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From: Mark Rutland <mark.rutland@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>,
	Young Xiao <92siuyang@gmail.com>,
	linux@armlinux.org.uk, mingo@redhat.com, bp@alien8.de,
	hpa@zytor.com, x86@kernel.org, kan.liang@linux.intel.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, 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
Date: Wed, 29 May 2019 17:24:36 +0100	[thread overview]
Message-ID: <20190529162435.GM31777@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20190529161955.GZ2623@hirez.programming.kicks-ass.net>

On Wed, May 29, 2019 at 06:19:55PM +0200, Peter Zijlstra wrote:
> On Wed, May 29, 2019 at 03:35:10PM +0100, Will Deacon wrote:
> > On Wed, May 29, 2019 at 03:25:15PM +0200, Peter Zijlstra wrote:
> > > 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.
> > 
> > So what should we report for the idle task?
> 
> If an interrupt hits the idle task, @regs would be !user_mode(regs),
> we'll find current->flags & PF_KTHREAD (idle not having passed through
> exec()) and therefore we'll take ABI_NONE for the user regs.
> 
> Or am I not getting it?

If the contents of task_pt_regs(current) is garbage, then the result of
user_mode(task_pt_regs(current)) is also garbage, no?

Thanks,
Mark.

WARNING: multiple messages have this Message-ID (diff)
From: Mark Rutland <mark.rutland@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Young Xiao <92siuyang@gmail.com>,
	mpe@ellerman.id.au, jolsa@redhat.com, x86@kernel.org,
	Will Deacon <will.deacon@arm.com>,
	linux@armlinux.org.uk, eranian@google.com,
	linux-kernel@vger.kernel.org, acme@redhat.com, mingo@redhat.com,
	bp@alien8.de, hpa@zytor.com, ravi.bangoria@linux.vnet.ibm.com,
	fweisbec@gmail.com, linux-arm-kernel@lists.infradead.org,
	kan.liang@linux.intel.com
Subject: Re: [PATCH] perf: Fix oops when kthread execs user process
Date: Wed, 29 May 2019 17:24:36 +0100	[thread overview]
Message-ID: <20190529162435.GM31777@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20190529161955.GZ2623@hirez.programming.kicks-ass.net>

On Wed, May 29, 2019 at 06:19:55PM +0200, Peter Zijlstra wrote:
> On Wed, May 29, 2019 at 03:35:10PM +0100, Will Deacon wrote:
> > On Wed, May 29, 2019 at 03:25:15PM +0200, Peter Zijlstra wrote:
> > > 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.
> > 
> > So what should we report for the idle task?
> 
> If an interrupt hits the idle task, @regs would be !user_mode(regs),
> we'll find current->flags & PF_KTHREAD (idle not having passed through
> exec()) and therefore we'll take ABI_NONE for the user regs.
> 
> Or am I not getting it?

If the contents of task_pt_regs(current) is garbage, then the result of
user_mode(task_pt_regs(current)) is also garbage, no?

Thanks,
Mark.

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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2019-05-29 16:24 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-28 12:31 [PATCH] perf: Fix oops when kthread execs user process Young Xiao
2019-05-28 12:31 ` Young Xiao
2019-05-28 12:41 ` Russell King - ARM Linux admin
2019-05-28 12:41   ` Russell King - ARM Linux admin
2019-05-28 14:01 ` Peter Zijlstra
2019-05-28 14:01   ` Peter Zijlstra
2019-05-28 15:32   ` Will Deacon
2019-05-28 15:32     ` Will Deacon
2019-05-28 16:12     ` Mark Rutland
2019-05-28 16:12       ` Mark Rutland
2019-05-28 17:32     ` Peter Zijlstra
2019-05-28 17:32       ` Peter Zijlstra
2019-05-29  9:17       ` Will Deacon
2019-05-29  9:17         ` Will Deacon
2019-05-29 10:10         ` Peter Zijlstra
2019-05-29 10:10           ` Peter Zijlstra
2019-05-29 10:20           ` Will Deacon
2019-05-29 10:20             ` Will Deacon
2019-05-29 12:55             ` Peter Zijlstra
2019-05-29 12:55               ` Peter Zijlstra
2019-05-29 13:05               ` Will Deacon
2019-05-29 13:05                 ` Will Deacon
2019-05-29 13:25                 ` Peter Zijlstra
2019-05-29 13:25                   ` Peter Zijlstra
2019-05-29 14:35                   ` Will Deacon
2019-05-29 14:35                     ` Will Deacon
2019-05-29 16:19                     ` Peter Zijlstra
2019-05-29 16:19                       ` Peter Zijlstra
2019-05-29 16:24                       ` Mark Rutland [this message]
2019-05-29 16:24                         ` Mark Rutland
2019-05-29 16:38                         ` Mark Rutland
2019-05-29 16:38                           ` Mark Rutland
2019-05-29 17:03                           ` Peter Zijlstra
2019-05-29 17:03                             ` Peter Zijlstra
2019-05-30 10:35                             ` Mark Rutland
2019-05-30 10:35                               ` Mark Rutland
2019-05-29 16:25                       ` Will Deacon
2019-05-29 16:25                         ` Will Deacon
2019-05-29 16:44                         ` Peter Zijlstra
2019-05-29 16:44                           ` Peter Zijlstra
2019-05-30  7:28                           ` Will Deacon
2019-05-30  7:28                             ` Will Deacon
2019-05-30  8:38               ` Ravi Bangoria
2019-05-30  8:38                 ` Ravi Bangoria
2019-05-30 10:27                 ` Ravi Bangoria
2019-05-30 10:27                   ` Ravi Bangoria
2019-05-31 15:37                   ` Will Deacon
2019-05-31 15:37                     ` Will Deacon
2019-06-03 11:23                     ` Will Deacon
2019-06-03 11:23                       ` Will Deacon
2019-06-03 11:48                     ` Peter Zijlstra
2019-06-03 11:48                       ` Peter Zijlstra
2019-06-03 13:30                     ` Michael Ellerman
2019-06-03 13:30                       ` Michael Ellerman
2019-05-29 10:11       ` Mark Rutland
2019-05-29 10:11         ` Mark Rutland
2019-05-29  4:21     ` Michael Ellerman
2019-05-29  4:21       ` Michael Ellerman
2019-05-29  1:44   ` Michael Ellerman
2019-05-29  1:44     ` Michael Ellerman

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