From: "Shi, Yang" <yang.shi@linaro.org> To: Will Deacon <will.deacon@arm.com>, James Morse <james.morse@arm.com> Cc: catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org Subject: Re: [PATCH] arm64: use raw_smp_processor_id in stack backtrace dump Date: Wed, 10 Feb 2016 10:12:11 -0800 [thread overview] Message-ID: <56BB7D7B.4060002@linaro.org> (raw) In-Reply-To: <20160210121030.GH1052@arm.com> On 2/10/2016 4:10 AM, Will Deacon wrote: > On Wed, Feb 10, 2016 at 11:52:31AM +0000, James Morse wrote: >> On 10/02/16 10:29, Will Deacon wrote: >>> On Tue, Feb 09, 2016 at 01:26:22PM -0800, Yang Shi wrote: >>>> dump_backtrace may be called in kthread context, which is not bound to a single >>>> cpu, i.e. khungtaskd, then calling smp_processor_id may trigger the below bug >>>> report: >>> >>> If we're preemptible here, it means that our irq_stack_ptr is potentially >>> bogus. Whilst this isn't an issue for kthreads, it does feel like we >>> could make this slightly more robust in the face of potential frame >>> corruption. Maybe just zero the IRQ stack pointer if we're in preemptible >>> context? >> >> Switching between stacks is only valid if we are tracing ourselves while on the >> irq_stack, we should probably prevent it for other tasks too. >> >> Something like (untested): >> --------------------- >> if (tsk == current && in_atomic()) >> irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id()); One follow up question, is it possible to have both tsk != current and on_irq_stack is true at the same time? If it is possible, this may be a problem in unwind_frame called by profile_pc which has tsk being NULL. Thanks, Yang >> else >> irq_stack_ptr = 0; >> --------------------- >> >> This would work when we trace ourselves while on the irq_stack, but break* >> tracing a running task on a remote cpu (khungtaskd doesn't do this). >> >> The same fix would apply to unwind_frame(), we have 'tsk' in both functions. >> >> Thoughts? > > in_atomic is a misnomer: > > https://lwn.net/Articles/274695/ > > ;) > > So we might be better off zeroing the pointer if tsk != current || > preemptible(). But yeah, I think we're in general agreement about this. > > Will >
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From: yang.shi@linaro.org (Shi, Yang) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] arm64: use raw_smp_processor_id in stack backtrace dump Date: Wed, 10 Feb 2016 10:12:11 -0800 [thread overview] Message-ID: <56BB7D7B.4060002@linaro.org> (raw) In-Reply-To: <20160210121030.GH1052@arm.com> On 2/10/2016 4:10 AM, Will Deacon wrote: > On Wed, Feb 10, 2016 at 11:52:31AM +0000, James Morse wrote: >> On 10/02/16 10:29, Will Deacon wrote: >>> On Tue, Feb 09, 2016 at 01:26:22PM -0800, Yang Shi wrote: >>>> dump_backtrace may be called in kthread context, which is not bound to a single >>>> cpu, i.e. khungtaskd, then calling smp_processor_id may trigger the below bug >>>> report: >>> >>> If we're preemptible here, it means that our irq_stack_ptr is potentially >>> bogus. Whilst this isn't an issue for kthreads, it does feel like we >>> could make this slightly more robust in the face of potential frame >>> corruption. Maybe just zero the IRQ stack pointer if we're in preemptible >>> context? >> >> Switching between stacks is only valid if we are tracing ourselves while on the >> irq_stack, we should probably prevent it for other tasks too. >> >> Something like (untested): >> --------------------- >> if (tsk == current && in_atomic()) >> irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id()); One follow up question, is it possible to have both tsk != current and on_irq_stack is true at the same time? If it is possible, this may be a problem in unwind_frame called by profile_pc which has tsk being NULL. Thanks, Yang >> else >> irq_stack_ptr = 0; >> --------------------- >> >> This would work when we trace ourselves while on the irq_stack, but break* >> tracing a running task on a remote cpu (khungtaskd doesn't do this). >> >> The same fix would apply to unwind_frame(), we have 'tsk' in both functions. >> >> Thoughts? > > in_atomic is a misnomer: > > https://lwn.net/Articles/274695/ > > ;) > > So we might be better off zeroing the pointer if tsk != current || > preemptible(). But yeah, I think we're in general agreement about this. > > Will >
next prev parent reply other threads:[~2016-02-10 18:12 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-02-09 21:26 [PATCH] arm64: use raw_smp_processor_id in stack backtrace dump Yang Shi 2016-02-09 21:26 ` Yang Shi 2016-02-10 10:29 ` Will Deacon 2016-02-10 10:29 ` Will Deacon 2016-02-10 11:52 ` James Morse 2016-02-10 11:52 ` James Morse 2016-02-10 12:10 ` Will Deacon 2016-02-10 12:10 ` Will Deacon 2016-02-10 18:12 ` Shi, Yang [this message] 2016-02-10 18:12 ` Shi, Yang 2016-02-11 10:41 ` James Morse 2016-02-11 10:41 ` James Morse 2016-02-11 17:36 ` Shi, Yang 2016-02-11 17:36 ` Shi, Yang
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