On Fri, 7 Aug 2015, Jeff Layton wrote: > On Fri, 7 Aug 2015 07:49:58 -0400 (EDT) > Benjamin Coddington <bcodding@xxxxxxxxxx> wrote: > > > On Wed, 22 Jul 2015, Jeff Layton wrote: > > > > > On Wed, 22 Jul 2015 11:34:41 -0400 > > > Benjamin Coddington <bcodding@xxxxxxxxxx> wrote: > > > > > > > Our QE folks are noticing the old leftover locks WARN popping up in RHEL7 > > > > (it's since been removed). While investigating upstream, I found I could > > > > make this happen by locking, then closing and signaling a process in a loop: > > > > > > > > #0 [ffff88007a4874a0] __schedule at ffffffff81736d8a > > > > #1 [ffff88007a4874f0] schedule at ffffffff81737407 > > > > #2 [ffff88007a487510] do_exit at ffffffff8109e18f > > > > #3 [ffff88007a487590] oops_end at ffffffff8101822e > > > > #4 [ffff88007a4875c0] no_context at ffffffff81063b55 > > > > #5 [ffff88007a487630] __bad_area_nosemaphore at ffffffff81063e1b > > > > #6 [ffff88007a487680] bad_area_nosemaphore at ffffffff81063fa3 > > > > #7 [ffff88007a487690] __do_page_fault at ffffffff81064251 > > > > #8 [ffff88007a4876f0] trace_do_page_fault at ffffffff81064677 > > > > #9 [ffff88007a487730] do_async_page_fault at ffffffff8105ed0e > > > > #10 [ffff88007a487750] async_page_fault at ffffffff8173d078 > > > > [exception RIP: nfs4_put_lock_state+82] > > > > RIP: ffffffffa02dd5b2 RSP: ffff88007a487808 RFLAGS: 00010207 > > > > RAX: 0000003fffffffff RBX: ffff8800351d2000 RCX: 0000000000000024 > > > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000009 > > > > RBP: ffff88007a487818 R8: 0000000000000000 R9: 0000000000000000 > > > > R10: 000000000000028b R11: 0000000000aaaaaa R12: ffff88003675e240 > > > > R13: ffff88003504d5b0 R14: ffff88007a487b30 R15: ffff880035097c40 > > > > ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 > > > > #11 [ffff88007a487800] nfs4_put_lock_state at ffffffffa02dd59b [nfsv4] > > > > #12 [ffff88007a487820] nfs4_fl_release_lock at ffffffffa02dd605 [nfsv4] > > > > #13 [ffff88007a487830] locks_release_private at ffffffff81258548 > > > > #14 [ffff88007a487850] locks_free_lock at ffffffff81258dbb > > > > #15 [ffff88007a487870] locks_dispose_list at ffffffff81258f68 > > > > #16 [ffff88007a4878a0] __posix_lock_file at ffffffff81259ab6 > > > > #17 [ffff88007a487930] posix_lock_inode_wait at ffffffff8125a02a > > > > #18 [ffff88007a4879b0] do_vfs_lock at ffffffffa02c4687 [nfsv4] > > > > #19 [ffff88007a4879c0] nfs4_proc_lock at ffffffffa02cc1a1 [nfsv4] > > > > #20 [ffff88007a487a70] do_unlk at ffffffffa0273d9e [nfs] > > > > #21 [ffff88007a487ac0] nfs_lock at ffffffffa0273fa9 [nfs] > > > > #22 [ffff88007a487b10] vfs_lock_file at ffffffff8125a76e > > > > #23 [ffff88007a487b20] locks_remove_posix at ffffffff8125a819 > > > > #24 [ffff88007a487c10] locks_remove_posix at ffffffff8125a878 > > > > #25 [ffff88007a487c20] filp_close at ffffffff812092a2 > > > > #26 [ffff88007a487c50] put_files_struct at ffffffff812290c5 > > > > #27 [ffff88007a487ca0] exit_files at ffffffff812291c1 > > > > #28 [ffff88007a487cc0] do_exit at ffffffff8109dc5f > > > > #29 [ffff88007a487d40] do_group_exit at ffffffff8109e3b5 > > > > #30 [ffff88007a487d70] get_signal at ffffffff810a9504 > > > > #31 [ffff88007a487e00] do_signal at ffffffff81014447 > > > > #32 [ffff88007a487f30] do_notify_resume at ffffffff81014b0e > > > > #33 [ffff88007a487f50] int_signal at ffffffff8173b2fc > > > > > > > > The nfs4_lock_state->ls_state pointer is pointing to free memory. > > > > > > > > I think what's happening here is that a signal is bumping us out of > > > > do_unlk() waiting on the io_counter while we try to release locks on > > > > __fput(). Since the lock is never released, it sticks around on the inode > > > > until another lock replaces it, and when it is freed it wants some bits from > > > > nfs4_state, but the nfs4_state was already cleaned up. > > > > > > > > Probably we need to do a better job not bailing out of do_unlk on file > > > > close, but while I work on that, something like the following keeps the > > > > nfs4_state around for proper cleanup of the nfs4_lock_state: > > > > > > > > Is this sane? > > > > > > > > Ben > > > > > > > > 8<-------------------------------------------------------------------- > > > > From cab3dd59aa1a04f3be28811dfb515afc4a9080a7 Mon Sep 17 00:00:00 2001 > > > > Message-Id: <cab3dd59aa1a04f3be28811dfb515afc4a9080a7.1437578183.git.bcodding@xxxxxxxxxx> > > > > From: Benjamin Coddington <bcodding@xxxxxxxxxx> > > > > Date: Wed, 22 Jul 2015 11:02:26 -0400 > > > > Subject: [PATCH] NFS: keep nfs4_state for nfs4_lock_state cleanup > > > > > > > > If we fail to release a lock due to an error or signal on file close, we > > > > might later free the lock if another lock replaces it. Hold a reference to > > > > the nfs4_state to ensure it is not released before freeing the > > > > nfs4_lock_state. > > > > --- > > > > fs/nfs/nfs4state.c | 2 ++ > > > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > > > > > diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c > > > > index 605840d..f93b410 100644 > > > > --- a/fs/nfs/nfs4state.c > > > > +++ b/fs/nfs/nfs4state.c > > > > @@ -827,6 +827,7 @@ static struct nfs4_lock_state *nfs4_alloc_lock_state(struct nfs4_state *state, f > > > > return NULL; > > > > nfs4_init_seqid_counter(&lsp->ls_seqid); > > > > atomic_set(&lsp->ls_count, 1); > > > > + atomic_inc(&state->count); > > > > lsp->ls_state = state; > > > > lsp->ls_owner = fl_owner; > > > > lsp->ls_seqid.owner_id = ida_simple_get(&server->lockowner_id, 0, 0, GFP_NOFS); > > > > @@ -903,6 +904,7 @@ void nfs4_put_lock_state(struct nfs4_lock_state *lsp) > > > > clp->cl_mvops->free_lock_state(server, lsp); > > > > } else > > > > nfs4_free_lock_state(server, lsp); > > > > + nfs4_put_open_state(state); > > > > } > > > > > > > > static void nfs4_fl_copy_lock(struct file_lock *dst, struct file_lock *src) > > > > > > Looks relatively harmless at first glance, and since lock states are > > > somewhat dependent on an open state then having them hold a reference > > > like this makes a lot of sense as well. > > > > > > The existing behavior is probably fine when FL_CLOSE isn't set, but > > > when it is we need a stronger guarantee that the lock will be cleaned > > > up properly. > > > > > > I think the best fix when FL_CLOSE is set would be to change the code > > > so that it's not waiting synchronously on the iocounter to go to zero > > > before submitting the rpc_task. Instead, we should have the LOCKU > > > rpc_task wait on an rpc_wait_queue for the counter to go to zero. > > > > > > We might be able to get away with making all LOCKU rpcs do this, but I > > > think when you catch a signal in the middle of a fcntl() syscall, > > > you'll probably want to cancel the RPC as well if it hasn't been > > > successfully transmitted yet. > > > > It seems like using a separate rpc_wait_queue to make sure the unlock is > > completed when the wait is interrupted would work for nfsv4, but for nlm > > locks it looks like a lot of plumbing. You'd have to decide to pass along > > the rpc_wait_queue or a callback way before you get anywhere near setting up > > a task, or give nlm the smarts to check the io_counters. Maybe I am being > > dense and there's a simpler way. > > > > I think it makes sense to instead add the unlock request to the io_counter, > > and have nfsiod do the unlock when the counter reaches zero. Somebody yell > > at me if that's a really bad idea. > > > > Ok, so you're going to add a list (or something) to nfs_io_counter. If > the wait is interrupted, you'll add the unlock request to the list. > When the io_count goes to 0, you'll submit all of the lock requests on > the list to nfsiod? > > I don't know...it seems like your plan would add some new special-case > machinery to handle this case when we already have the necessary > infrastructure to do it with rpc_wait_queues. > > My thinking was to just create a global rpc_wait_queue for this. Any > rpc_task that needs to wait on an io_count to drop would wait on this > queue, and when any NFS io_count drops to 0, you wake up all the > waiters. If the rpc_task is scheduled and finds that the io_count for > the inode is not 0, it goes back to sleep on the wait queue. > > The symbol for the queue could be exported so that both NLM and > NFS could access it -- maybe it could live in fs/nfs_common? > > For NLM then you'd just need to add a rpc_call_prepare operation for > nlmclnt_unlock_ops that does this check and puts the task to sleep on > this wait queue if the io_count is still high. > > The one case that does not cover though is the "is_local" case in > do_unlk. You probably would still need to do a synchronous wait there, > or come up with some other mechanism to handle it. Queueing the unlock > to a workqueue may make sense there. > > In any case, it's ultimately up to Trond/Anna since they'd be the ones > merging this. If they think your proposal is a better way to go, then > I'm fine with that. Yes, your description is what I was thinking. While the sheduling infrastructure exists to do it with rpc_wait_queue, it seemed a bit of a overload to use them for delayed work when the conditions for the delay are removed from the rpc layer. I was wondering if that might create situations where we repeatedly check many io_counters unnecessarily when every io_counter reaches zero. It does look like the return-on-close stuff uses them for this purpose, however, so maybe it is appropriate. My thinking was that the nfsiod workqueue was originally created to handle this sort of work; I thought I'd follow the way put_nfs_open_context works to call close. Thanks for your comments and help. Ben -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
