On Mon 02-01-17 16:11:36, Johannes Weiner wrote: > On Fri, Dec 23, 2016 at 03:33:29AM -0500, Johannes Weiner wrote: > > 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. > > Sorry for dropping silent on this. I'm traveling over the holidays > with sporadic access to my emails and no access to real equipment. > > The times I managed to sneak away to look at the code didn't turn up > anything useful yet. > > Andrea encountered the warning as well and I gave him a debugging > patch (attached below), but he hasn't been able to reproduce this > condition. I've personally never seen the warning trigger, even though > the patches have been running on my main development machine for quite > a while now. Albeit against an older base; I've updated to Linus's > master branch now in case it's an interaction with other new code. > > If anybody manages to reproduce this, that would be helpful. Any extra > eyes on this would be much appreciated too until I'm back at my desk. I was looking into this but I didn't find a way how we could possibly leave radix tree node on LRU. So your debug patch looks like a good way forward. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
