From c9399f21c215453b414702758b8c4b7d66605eac Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Mon, 6 Nov 2017 15:28:01 -0500 Subject: NFSv4: Fix OPEN / CLOSE race Ben Coddington has noted the following race between OPEN and CLOSE on a single client. Process 1 Process 2 Server ========= ========= ====== 1) OPEN file 2) OPEN file 3) Process OPEN (1) seqid=1 4) Process OPEN (2) seqid=2 5) Reply OPEN (2) 6) Receive reply (2) 7) new stateid, seqid=2 8) CLOSE file, using stateid w/ seqid=2 9) Reply OPEN (1) 10( Process CLOSE (8) 11) Reply CLOSE (8) 12) Forget stateid file closed 13) Receive reply (7) 14) Forget stateid file closed. 15) Receive reply (1). 16) New stateid seqid=1 is really the same stateid that was closed. IOW: the reply to the first OPEN is delayed. Since "Process 2" does not wait before closing the file, and it does not cache the closed stateid, then when the delayed reply is finally received, it is treated as setting up a new stateid by the client. The fix is to ensure that the client processes the OPEN and CLOSE calls in the same order in which the server processed them. This commit ensures that we examine the seqid of the stateid returned by OPEN. If it is a new stateid, we assume the seqid must be equal to the value 1, and that each state transition increments the seqid value by 1 (See RFC7530, Section 9.1.4.2, and RFC5661, Section 8.2.2). If the tracker sees that an OPEN returns with a seqid that is greater than the cached seqid + 1, then it bumps a flag to ensure that the caller waits for the RPCs carrying the missing seqids to complete. Note that there can still be pathologies where the server crashes before it can even send us the missing seqids. Since the OPEN call is still holding a slot when it waits here, that could cause the recovery to stall forever. To avoid that, we time out after a 5 second wait. Reported-by: Benjamin Coddington Signed-off-by: Trond Myklebust Signed-off-by: Anna Schumaker --- fs/nfs/nfs4state.c | 1 + 1 file changed, 1 insertion(+) (limited to 'fs/nfs/nfs4state.c') diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c index 3bd79b8c016b..6e3f37288348 100644 --- a/fs/nfs/nfs4state.c +++ b/fs/nfs/nfs4state.c @@ -645,6 +645,7 @@ nfs4_alloc_open_state(void) INIT_LIST_HEAD(&state->lock_states); spin_lock_init(&state->state_lock); seqlock_init(&state->seqlock); + init_waitqueue_head(&state->waitq); return state; } -- cgit v1.2.1