Messages in this thread | | | Date | Tue, 20 Dec 2016 11:59:40 -0500 | Subject | Re: Debug hints for fpu state NULL pointer dereference on context switch during core dump in 3.0.101 | From | (Lennart Sorensen) |
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On Mon, Dec 19, 2016 at 01:09:39PM -0500, Lennart Sorensen wrote: > I am trying to debug a problem that has been happening occationally for > years on some of our systems running 3.0.101 kernel (yes I know it is > old, we are moving to 4.9 at the moment but I would like older releases > to be fixed too, assuming 4.9 makes this problem disappear). > > What is happening is that once in a while a process does something wrong > and segfaults, and dumps core. We have a handler to process the core dump > to name it and compress it and make sure we don't keep to many around, > so the core_pattern uses the pipe option to pipe the dump to a shell > script that saves it with the pid and current timestamp and gzips it. > > Once in a while when this happens, the kernel hits a null pointer > dereference in fpu.state->xsave while doing __switch_to. > > The system ix x86_64 with dual E5-2620 CPUs (6 cores each with > hyperthreading). Some people think they have seen it on other systems, > but are not sure. I have not been able to trigger it on other systems > yet. > > It used to take about a week of running tests to trigger it, but I have > now managed to hit it in a few minutes pretty reliably.
If the core_pattern is not set to use a pipe, but just save as core.%e.%p then the problem does not happen.
-- Len Sorensen
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