>[Please do not top post - thank you] >[CC Hugh - the original patch was http://lkml.kernel.org/r/2018072514375722198958@xxxxxxxxxxxx] > >On Wed 25-07-18 15:57:55, zhaowuyun@xxxxxxxxxxxx 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 Hi Michal, The action what processes __read_swap_cache_async is on the process context, so I think disable preemption is enough. -------------- zhaowuyun@xxxxxxxxxxxx
