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. That block comment over `struct select_data' is not a good one. "It returns zero iff...". *What* returns zero? select_collect()? No it doesn't, it returns an `enum d_walk_ret'. Perhaps the comment is trying to refer to select_data.found. And the real interpretation of select_data.found is, umm, hard to describe. "Counts the number of dentries which are on a shrink list or which were moved to the dispose list". Why? What's that all about? This code needs a bit of thought, documentation and perhaps a redo, I suspect.
