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/[email protected]]
now for real > On Wed 25-07-18 15:57:55, [email protected] 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
