From 9a99af494bd7141d567d00b5ef94b141821e158c Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Mon, 4 Feb 2013 20:17:49 -0500 Subject: NFSv4.1: Prevent deadlocks between state recovery and file locking We currently have a deadlock in which the state recovery thread ends up blocking due to one of the locks which it is trying to recover holding the nfs_inode->rwsem. The situation is as follows: the state recovery thread is scheduled in order to recover from a reboot. It immediately drains the session, forcing all ordinary NFSv4.1 calls to nfs41_setup_sequence() to be put to sleep. This includes the file locking process that holds the nfs_inode->rwsem. When the thread gets to nfs4_reclaim_locks(), it tries to grab a write lock on nfs_inode->rwsem, and boom... Fix is to have the lock drop the nfs_inode->rwsem while it is doing RPC calls. We use a sequence lock in order to signal to the locking process whether or not a state recovery thread has run on that inode, in which case it should retry the lock. Reported-by: Andy Adamson Signed-off-by: Trond Myklebust --- fs/nfs/nfs4proc.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'fs/nfs') diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c index 62fa4001e47a..92584c1ea725 100644 --- a/fs/nfs/nfs4proc.c +++ b/fs/nfs/nfs4proc.c @@ -4813,8 +4813,10 @@ static int nfs41_lock_expired(struct nfs4_state *state, struct file_lock *reques static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock *request) { + struct nfs4_state_owner *sp = state->owner; struct nfs_inode *nfsi = NFS_I(state->inode); unsigned char fl_flags = request->fl_flags; + unsigned int seq; int status = -ENOLCK; if ((fl_flags & FL_POSIX) && @@ -4836,9 +4838,16 @@ static int _nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock status = do_vfs_lock(request->fl_file, request); goto out_unlock; } + seq = raw_seqcount_begin(&sp->so_reclaim_seqcount); + up_read(&nfsi->rwsem); status = _nfs4_do_setlk(state, cmd, request, NFS_LOCK_NEW); if (status != 0) + goto out; + down_read(&nfsi->rwsem); + if (read_seqcount_retry(&sp->so_reclaim_seqcount, seq)) { + status = -NFS4ERR_DELAY; goto out_unlock; + } /* Note: we always want to sleep here! */ request->fl_flags = fl_flags | FL_SLEEP; if (do_vfs_lock(request->fl_file, request) < 0) -- cgit v1.2.3