Messages in this thread | | | Subject | Re: [PATCH 2/2] mm, oom: fix potential data corruption when oom_reaper races with writer | From | Tetsuo Handa <> | Date | Fri, 11 Aug 2017 16:54:36 +0900 |
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Michal Hocko wrote: > On Fri 11-08-17 11:28:52, Tetsuo Handa wrote: > > Michal Hocko wrote: > > > +/* > > > + * Checks whether a page fault on the given mm is still reliable. > > > + * This is no longer true if the oom reaper started to reap the > > > + * address space which is reflected by MMF_UNSTABLE flag set in > > > + * the mm. At that moment any !shared mapping would lose the content > > > + * and could cause a memory corruption (zero pages instead of the > > > + * original content). > > > + * > > > + * User should call this before establishing a page table entry for > > > + * a !shared mapping and under the proper page table lock. > > > + * > > > + * Return 0 when the PF is safe VM_FAULT_SIGBUS otherwise. > > > + */ > > > +static inline int check_stable_address_space(struct mm_struct *mm) > > > +{ > > > + if (unlikely(test_bit(MMF_UNSTABLE, &mm->flags))) > > > + return VM_FAULT_SIGBUS; > > > + return 0; > > > +} > > > + > > > > Will you explain the mechanism why random values are written instead of zeros > > so that this patch can actually fix the race problem? > > I am not sure what you mean here. Were you able to see a write with an > unexpected content?
Yes. See http://lkml.kernel.org/r/201708072228.FAJ09347.tOOVOFFQJSHMFL@I-love.SAKURA.ne.jp .
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