Messages in this thread | | | Date | Wed, 25 Jul 2018 12:32:04 +0200 | From | Michal Hocko <> | Subject | Re: Re: [PATCH] [PATCH] mm: disable preemption before swapcache_free |
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On Wed 25-07-18 10:21:00, Michal Hocko wrote: > [Please do not top post - thank you] > [CC Hugh - the original patch was http://lkml.kernel.org/r/2018072514375722198958@wingtech.com]
now for real
> On Wed 25-07-18 15:57:55, zhaowuyun@wingtech.com wrote: > > That is a BUG we found in mm/vmscan.c at KERNEL VERSION 4.9.82 > > The code is quite similar in the current tree as well. > > > Sumary is TASK A (normal priority) doing __remove_mapping page preempted by TASK B (RT priority) doing __read_swap_cache_async, > > the TASK A preempted before swapcache_free, left SWAP_HAS_CACHE flag in the swap cache, > > the TASK B which doing __read_swap_cache_async, will not success at swapcache_prepare(entry) because the swap cache was exist, then it will loop forever because it is a RT thread... > > the spin lock unlocked before swapcache_free, so disable preemption until swapcache_free executed ... > > OK, I see your point now. I have missed the lock is dropped before > swapcache_free. How can preemption disabling prevent this race to happen > while the code is preempted by an IRQ?
-- Michal Hocko SUSE Labs
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