Messages in this thread | | | Date | Thu, 1 Mar 2018 10:35:22 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH] Detect early free of a live mm |
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On Wed 28-02-18 12:18:10, Mark Rutland wrote: > Ugh, I messed up Peter's email when sending this out. please > s/infraded/infradead/ if replying to the first mail. > > Sorry about that. > > Mark. > > On Wed, Feb 28, 2018 at 12:14:58PM +0000, Mark Rutland wrote: > > KASAN splats indicate that in some cases we free a live mm, then > > continue to access it, with potentially disastrous results. This is > > likely due to a mismatched mmdrop() somewhere in the kernel, but so far > > the culprit remains elusive. > > > > Let's have __mmdrop() verify that the mm isn't live for the current > > task, similar to the existing check for init_mm. This way, we can catch > > this class of issue earlier, and without requiring KASAN.
Wouldn't it be better to check the mm_users count instead? {VM_}BUG_ON(atomic_read(&mm->mm_users));
Relying on current->mm resetting works currently but this is quite a subtle dependency. -- Michal Hocko SUSE Labs
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