From 137d6acaa64afa4cf3d977417424e731ea04705a Mon Sep 17 00:00:00 2001 From: Frank Filz Date: Mon, 9 Jul 2007 15:32:29 -0700 Subject: [PATCH] NFSv4: Make sure unlock is really an unlock when cancelling a lock I ran into a curious issue when a lock is being canceled. The cancellation results in a lock request to the vfs layer instead of an unlock request. This is particularly insidious when the process that owns the lock is exiting. In that case, sometimes the erroneous lock is applied AFTER the process has entered zombie state, preventing the lock from ever being released. Eventually other processes block on the lock causing a slow degredation of the system. In the 2.6.16 kernel this was investigated on, the problem is compounded by the fact that the cl_sem is held while blocking on the vfs lock, which results in most processes accessing the nfs file system in question hanging. In more detail, here is how the situation occurs: first _nfs4_do_setlk(): static int _nfs4_do_setlk(struct nfs4_state *state, int cmd, struct file_lock *fl, int reclaim) ... ret = nfs4_wait_for_completion_rpc_task(task); if (ret == 0) { ... } else data->cancelled = 1; then nfs4_lock_release(): static void nfs4_lock_release(void *calldata) ... if (data->cancelled != 0) { struct rpc_task *task; task = nfs4_do_unlck(&data->fl, data->ctx, data->lsp, data->arg.lock_seqid); The problem is the same file_lock that was passed in to _nfs4_do_setlk() gets passed to nfs4_do_unlck() from nfs4_lock_release(). So the type is still F_RDLCK or FWRLCK, not F_UNLCK. At some point, when cancelling the lock, the type needs to be changed to F_UNLCK. It seemed easiest to do that in nfs4_do_unlck(), but it could be done in nfs4_lock_release(). The concern I had with doing it there was if something still needed the original file_lock, though it turns out the original file_lock still needs to be modified by nfs4_do_unlck() because nfs4_do_unlck() uses the original file_lock to pass to the vfs layer, and a copy of the original file_lock for the RPC request. It seems like the simplest solution is to force all situations where nfs4_do_unlck() is being used to result in an unlock, so with that in mind, I made the following change: Signed-off-by: Frank Filz Signed-off-by: Trond Myklebust --- fs/nfs/nfs4proc.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c index ba86ec654c2e..fee2da856c95 100644 --- a/fs/nfs/nfs4proc.c +++ b/fs/nfs/nfs4proc.c @@ -3275,6 +3275,11 @@ static struct rpc_task *nfs4_do_unlck(struct file_lock *fl, { struct nfs4_unlockdata *data; + /* Ensure this is an unlock - when canceling a lock, the + * canceled lock is passed in, and it won't be an unlock. + */ + fl->fl_type = F_UNLCK; + data = nfs4_alloc_unlockdata(fl, ctx, lsp, seqid); if (data == NULL) { nfs_free_seqid(seqid);