Messages in this thread | | | Date | Wed, 18 Jun 2008 10:42:19 +0200 | From | Patrick McHardy <> | Subject | Re: 2.6.26-git: NULL pointer deref in __switch_to |
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Suresh Siddha wrote: > Simon, Patrick, I am able to reproduce the oops in __switch_to() > with lguest. My debug showed that there is atleast one lguest specific > issue (which should be present in 2.6.25 and before aswell) and it got > exposed with a kernel oops with the recent fpu dynamic allocation patches. > > In addition to the previous possible scenario (with fpu_counter), in the > presence of lguest, it is possible that the cpu's TS bit it still set and the > lguest launcher task's thread_info has TS_USEDFPU still set. > > This is because of the way the lguest launcher handling the guest's TS bit. > (look at lguest_set_ts() in lguest_arch_run_guest()). This can result > in a DNA fault while doing unlazy_fpu() in __switch_to(). This will > end up causing a DNA fault in the context of new process thats > getting context switched in (as opossed to handling DNA fault in the context > of lguest launcher/helper process). > > This is wrong in both pre and post 2.6.25 kernels. In the recent > 2.6.26-rc series, this is showing up as NULL pointer dereferences or > sleeping function called from atomic context(__switch_to()), as > we free and dynamically allocate the FPU context for the newly > created threads. Older kernels might show some FPU corruption for processes > running inside of lguest. > > With the appended patch, my test system is running for more than 50 mins > now. So atleast some of your oops (hopefully all!) should get fixed. > Please give it a try. I will spend more time with this fix tomorrow. > > Apart from the last hunk(MSR_IA32_SYSENTER_CS changes), I believe > the below patch is needed for 2.6.25 aswell. >
The patch seems to have fixed the problem for me, thanks Suresh.
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