On Fri, Dec 23, 2016 at 02:32:41AM -0500, Johannes Weiner wrote: > On Thu, Dec 22, 2016 at 12:22:27PM -0800, Hugh Dickins wrote: > > On Wed, 21 Dec 2016, Linus Torvalds wrote: > > > On Wed, Dec 21, 2016 at 9:13 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > > I unmounted the fs, mkfs'd it again, ran the > > > > workload again and about a minute in this fired: > > > > > > > > [628867.607417] ------------[ cut here ]------------ > > > > [628867.608603] WARNING: CPU: 2 PID: 16925 at mm/workingset.c:461 shadow_lru_isolate+0x171/0x220 > > > > > > Well, part of the changes during the merge window were the shadow > > > entry tracking changes that came in through Andrew's tree. Adding > > > Johannes Weiner to the participants. > > > > > > > Now, this workload does not touch the page cache at all - it's > > > > entirely an XFS metadata workload, so it should not really be > > > > affecting the working set code. > > > > > > Well, I suspect that anything that creates memory pressure will end up > > > triggering the working set code, so .. > > > > > > That said, obviously memory corruption could be involved and result in > > > random issues too, but I wouldn't really expect that in this code. > > > > > > It would probably be really useful to get more data points - is the > > > problem reliably in this area, or is it going to be random and all > > > over the place. > > > > Data point: kswapd got WARNING on mm/workingset.c:457 in shadow_lru_isolate, > > soon followed by NULL pointer deref in list_lru_isolate, one time when > > I tried out Sunday's git tree. Not seen since, I haven't had time to > > investigate, just set it aside as something to worry about if it happens > > again. But it looks like shadow_lru_isolate() has issues beyond Dave's > > case (I've no XFS and no iscsi), suspect unrelated to his other problems. > > This seems consistent with what Dave observed: we encounter regular > pages in radix tree nodes on the shadow LRU that should only contain > nodes full of exceptional shadow entries. It could be an issue in the > new slot replacement code and the node tracking callback. Both encounters seem to indicate use-after-free. Dave's node didn't warn about an unexpected node->count / node->exceptional state, but had entries that were inconsistent with that. Hugh got the counter warning but crashed on a list_head that's not NULLed in a live node. workingset_update_node() should be called on page cache radix tree leaf nodes that go empty. I must be missing an update_node callback where a leaf node gets freed somewhere. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
