Messages in this thread | | | Subject | Re: 2.6.26-git: NULL pointer deref in __switch_to | From | Simon Holm Thøgersen <> | Date | Wed, 18 Jun 2008 15:57:54 +0200 |
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tir, 17 06 2008 kl. 16:50 -0700, skrev Suresh Siddha: > On Mon, Jun 16, 2008 at 02:21:23PM -0700, Simon Holm Thøgersen wrote: > > > Can you please upload it some where? I will also try with another guest > > > image meanwhile. > > > > > [access provided to Suresh in private email] > > Simon, Thanks. > > 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. > > Thanks. > > Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Thanks a lot Suresh, this fixes the issue for me. Feel free to add
Tested-by: Simon Holm Thøgersen <odie@cs.aau.dk>
Simon
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