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
