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Message-ID: <20130626081509.GF28748@dhcp22.suse.cz> Date: Wed, 26 Jun 2013 10:15:09 +0200 From: Michal Hocko <mhocko@...e.cz> To: Dave Chinner <david@...morbit.com> Cc: Glauber Costa <glommer@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: linux-next: slab shrinkers: BUG at mm/list_lru.c:92 On Tue 25-06-13 12:27:54, Dave Chinner wrote: > On Tue, Jun 18, 2013 at 03:50:25PM +0200, Michal Hocko wrote: > > And again, another hang. It looks like the inode deletion never > > finishes. The good thing is that I do not see any LRU related BUG_ONs > > anymore. I am going to test with the other patch in the thread. > > > > 2476 [<ffffffff8118325e>] __wait_on_freeing_inode+0x9e/0xc0 <<< waiting for an inode to go away > > [<ffffffff81183321>] find_inode_fast+0xa1/0xc0 > > [<ffffffff8118525f>] iget_locked+0x4f/0x180 > > [<ffffffff811ef9e3>] ext4_iget+0x33/0x9f0 > > [<ffffffff811f6a1c>] ext4_lookup+0xbc/0x160 > > [<ffffffff81174ad0>] lookup_real+0x20/0x60 > > [<ffffffff81177e25>] lookup_open+0x175/0x1d0 > > [<ffffffff8117815e>] do_last+0x2de/0x780 <<< holds i_mutex > > [<ffffffff8117ae9a>] path_openat+0xda/0x400 > > [<ffffffff8117b303>] do_filp_open+0x43/0xa0 > > [<ffffffff81168ee0>] do_sys_open+0x160/0x1e0 > > [<ffffffff81168f9c>] sys_open+0x1c/0x20 > > [<ffffffff81582fe9>] system_call_fastpath+0x16/0x1b > > [<ffffffffffffffff>] 0xffffffffffffffff > > I don't think this has anything to do with LRUs. I am not claiming that. It might be a timing issue which never mattered but it is strange I can reproduce this so easily and repeatedly with the shrinkers patchset applied. As I said earlier, this might be breakage in my -mm tree as well (missing some patch which didn't go via Andrew or misapplied patch). The situation is worsen by the state of linux-next which has some unrelated issues. I really do not want to delay the whole patchset just because of some problem on my side. Do you have any tree that I should try to test? > __wait_on_freeing_inode() only blocks once the inode is being freed > (i.e. I_FREEING is set), and that happens when a lookup is done when > the inode is still in the inode hash. > > I_FREEING is set on the inode at the same time it is removed from > the LRU, and from that point onwards the LRUs play no part in the > inode being freed and anyone waiting on the inode being freed > getting woken. > > The only way I can see this happening, is if there is a dispose list > that is not getting processed properly. e.g., we move a bunch on > inodes to the dispose list setting I_FREEING, then for some reason > it gets dropped on the ground and so the wakeup call doesn't happen > when the inode has been removed from the hash. > > I can't see anywhere in the code that this happens, though, but it > might be some pre-existing race in the inode hash that you are now > triggering because freeing will be happening in parallel on multiple > nodes rather than serialising on a global lock... > > I won't have seen this on XFS stress testing, because it doesn't use > the VFS inode hashes for inode lookups. Given that XFS is not > triggering either problem you are seeing, that makes me think I haven't tested with xfs. > that it might be a pre-existing inode hash lookup/reclaim race > condition, not a LRU problem. > > Cheers, > > Dave. > -- > Dave Chinner > david@...morbit.com -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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