On 01/14/2015 09:27 AM, Jeff Layton wrote: > On Tue, 13 Jan 2015 17:50:45 -0500 > Sasha Levin <sasha.levin@xxxxxxxxxx> wrote: > >> On 01/13/2015 04:44 PM, Jeff Layton wrote: >>> On Tue, 13 Jan 2015 00:11:37 -0500 >>> Sasha Levin <sasha.levin@xxxxxxxxxx> wrote: >>> >>>> Hey Jeff, >>>> >>>> While fuzzing with trinity inside a KVM tools guest running the latest -next >>>> kernel, I've stumbled on the following spew: >>>> >>>> [ 887.078606] WARNING: CPU: 16 PID: 4296 at fs/locks.c:236 locks_free_lock_context+0x10d/0x240() >>>> [ 887.079703] Modules linked in: >>>> [ 887.080288] CPU: 16 PID: 4296 Comm: trinity-c273 Not tainted 3.19.0-rc4-next-20150112-sasha-00053-g23c147e02e-dirty #1710 >>>> [ 887.082229] 0000000000000000 0000000000000000 0000000000000000 ffff8804c9f4f8e8 >>>> [ 887.083773] ffffffff9154e0a6 0000000000000000 ffff8804cad98000 ffff8804c9f4f938 >>>> [ 887.085280] ffffffff8140a4d0 0000000000000001 ffffffff81bf0d2d ffff8804c9f4f988 >>>> [ 887.086792] Call Trace: >>>> [ 887.087320] dump_stack (lib/dump_stack.c:52) >>>> [ 887.088247] warn_slowpath_common (kernel/panic.c:447) >>>> [ 887.089342] ? locks_free_lock_context (fs/locks.c:236 (discriminator 3)) >>>> [ 887.090514] warn_slowpath_null (kernel/panic.c:481) >>>> [ 887.091629] locks_free_lock_context (fs/locks.c:236 (discriminator 3)) >>>> [ 887.092782] __destroy_inode (fs/inode.c:243) >>>> [ 887.093817] destroy_inode (fs/inode.c:268) >>>> [ 887.094833] evict (fs/inode.c:574) >>>> [ 887.095808] iput (fs/inode.c:1503) >>>> [ 887.096687] __dentry_kill (fs/dcache.c:323 fs/dcache.c:508) >>>> [ 887.097683] ? _raw_spin_trylock (kernel/locking/spinlock.c:136) >>>> [ 887.098733] ? dput (fs/dcache.c:545 fs/dcache.c:648) >>>> [ 887.099672] dput (fs/dcache.c:649) >>>> [ 887.100552] __fput (fs/file_table.c:227) >>> >>> So, looking at this a bit more... >>> >>> It's clear that we're at the dput in __fput at this point. Much earlier >>> in __fput, we call locks_remove_file to remove all of the locks that >>> are associated with the file description. >>> >>> Evidently though, something didn't go right there. The two most likely >>> scenarios to my mind are: >>> >>> A) a lock raced onto the list somehow after that point. That seems >>> unlikely since presumably the fcheck should have failed at that point. >>> >>> ...or... >>> >>> B) the CPU that called locks_remove_file mistakenly thought that >>> inode->i_flctx was NULL when it really wasn't (stale cache, perhaps?). >>> That would make it skip trying to remove any flock locks. >>> >>> B seems more likely to me, and if it's the case then that would seem to >>> imply that we need some memory barriers (or maybe some ACCESS_ONCE >>> calls) in these codepaths. I'll have to sit down and work through it to >>> see what makes the most sense. >>> >>> If your debugging seems to jive with this, then one thing that might be >>> interesting would be to comment out these two lines in >>> locks_remove_flock: >>> >>> if (!file_inode(filp)->i_flctx) >>> return; >>> >>> ...and see if it's still reproducible. That's obviously not a real fix >>> for this problem, but it might help prove whether the above suspicion >>> is correct. >> >> Removing those two lines makes the issue go away. >> >> I'm guessing that figuring out which filesystem we were abusing isn't >> interesting anymore... >> > > Sigh. I've been trying to reproduce this today. I've set up two > different KVM guests on two different hosts, and run trinity on both, > and I can't seem to get this warning to pop. > > Could you share what trinity command-line options you're using? Any > other special setup I should be considering to reproduce it? > > I was hoping to get it to reproduce so I could test out potential > memory barrier fixes... I don't think there's anything special about my setup here that can trigger that, specially if it's not dependant on a filesystem in use. I'm running trinity with: ./trinity -xsched_setattr -xsetpriority -xunshare -xreboot -xshutdown -xnfsservctl -xclock_nanosleep -xuselib -xperf_event_open -m --quiet --dangerous -C 400 -l off If that doesn't end up helping, I'd be happy to test out fixes here, it usually reproduces quickly. Thanks, Sasha -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
