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From: Michael Ellerman <mpe@ellerman.id.au>
To: Peter Zijlstra <peterz@infradead.org>, Young Xiao <92siuyang@gmail.com>
Cc: will.deacon@arm.com, linux@armlinux.org.uk, mark.rutland@arm.com,
	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
Subject: Re: [PATCH] perf: Fix oops when kthread execs user process
Date: Wed, 29 May 2019 11:44:02 +1000	[thread overview]
Message-ID: <87a7f6ox0d.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20190528140103.GT2623@hirez.programming.kicks-ass.net>

Peter Zijlstra <peterz@infradead.org> writes:
> On Tue, May 28, 2019 at 08:31:29PM +0800, Young Xiao wrote:
>> When a kthread calls call_usermodehelper() the steps are:
>>   1. allocate current->mm
>>   2. load_elf_binary()
>>   3. populate current->thread.regs
>> 
>> While doing this, interrupts are not disabled. If there is a perf
>> interrupt in the middle of this process (i.e. step 1 has completed
>> but not yet reached to step 3) and if perf tries to read userspace
>> regs, kernel oops.
>> 
>> Fix it by setting abi to PERF_SAMPLE_REGS_ABI_NONE when userspace
>> pt_regs are not set.
>> 
>> See commit bf05fc25f268 ("powerpc/perf: Fix oops when kthread execs
>> user process") for details.
>
> Why the hell do we set current->mm before it is complete? Note that
> normally exec() builds the new mm before attaching it, see exec_mmap()
> in flush_old_exec().
>
> Also, why did those PPC folks 'fix' this in isolation? And why didn't
> you Cc them?

We just assumed it was our bug, 'cause we have plenty of those :)

cheers

WARNING: multiple messages have this Message-ID (diff)
From: Michael Ellerman <mpe@ellerman.id.au>
To: Peter Zijlstra <peterz@infradead.org>, Young Xiao <92siuyang@gmail.com>
Cc: mark.rutland@arm.com, x86@kernel.org, will.deacon@arm.com,
	linux@armlinux.org.uk, linux-kernel@vger.kernel.org,
	mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
	ravi.bangoria@linux.vnet.ibm.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 11:44:02 +1000	[thread overview]
Message-ID: <87a7f6ox0d.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20190528140103.GT2623@hirez.programming.kicks-ass.net>

Peter Zijlstra <peterz@infradead.org> writes:
> On Tue, May 28, 2019 at 08:31:29PM +0800, Young Xiao wrote:
>> When a kthread calls call_usermodehelper() the steps are:
>>   1. allocate current->mm
>>   2. load_elf_binary()
>>   3. populate current->thread.regs
>> 
>> While doing this, interrupts are not disabled. If there is a perf
>> interrupt in the middle of this process (i.e. step 1 has completed
>> but not yet reached to step 3) and if perf tries to read userspace
>> regs, kernel oops.
>> 
>> Fix it by setting abi to PERF_SAMPLE_REGS_ABI_NONE when userspace
>> pt_regs are not set.
>> 
>> See commit bf05fc25f268 ("powerpc/perf: Fix oops when kthread execs
>> user process") for details.
>
> Why the hell do we set current->mm before it is complete? Note that
> normally exec() builds the new mm before attaching it, see exec_mmap()
> in flush_old_exec().
>
> Also, why did those PPC folks 'fix' this in isolation? And why didn't
> you Cc them?

We just assumed it was our bug, 'cause we have plenty of those :)

cheers

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  parent reply	other threads:[~2019-05-29  1:44 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
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 [this message]
2019-05-29  1:44     ` Michael Ellerman

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