On Sat, Apr 14, 2018 at 10:00:29AM +0300, Nikolay Borisov wrote: > > > On 14.04.2018 00:14, Andrew Morton wrote: > > On Fri, 13 Apr 2018 13:28:23 -0700 Khazhismel Kumykov <khazhy@xxxxxxxxxx> wrote: > > > >> shrink_dcache_parent may spin waiting for a parallel shrink_dentry_list. > >> In this case we may have 0 dentries to dispose, so we will never > >> schedule out while waiting for the parallel shrink_dentry_list to > >> complete. > >> > >> Tested that this fixes syzbot reports of stalls in shrink_dcache_parent() > > > > Well I guess the patch is OK as a stopgap, but things seem fairly > > messed up in there. shrink_dcache_parent() shouldn't be doing a > > busywait, waiting for the concurrent shrink_dentry_list(). > > > > Either we should be waiting (sleeping) for the concurrent operation to > > complete or we should just bail out of shrink_dcache_parent(), perhaps > > with > > > > if (list_empty(&data.dispose)) > > break; > > > > or similar. Dunno. > > I agree, however, not being a dcache expert I'd refrain from touching > it, since it seems to be rather fragile. Perhaps Al could take a look in > there? "Bail out" is definitely a bad idea, "sleep"... what on? Especially since there might be several evictions we are overlapping with...
