>On Wed 25-07-18 17:53:07, zhaowuyun@xxxxxxxxxxxx wrote: >> >[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. > >So what you are saying is that no IRQ or other non-process contexts will >not loop in __read_swap_cache_async so the live lock is not possible? >-- >Michal Hocko >SUSE Labs I think that __read_swap_cache_async will not running under IRQ contexts. If running under other non-process contexts, I think it must at the other CPU, will not encounter this dead loop. -------------- zhaowuyun@xxxxxxxxxxxx
