Messages in this thread | | | Subject | Re: [PATCH] arm64: use raw_smp_processor_id in stack backtrace dump | From | "Shi, Yang" <> | Date | Wed, 10 Feb 2016 10:12:11 -0800 |
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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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