[PATCH 4.4 057/137] nfs: Fix race in __update_open_stateid()

Greg Kroah-Hartman
2016-02-24T04:42:38Z

From: Andrew Elble <aweits@rit.edu>

commit 361cad3c89070aeb37560860ea8bfc092d545adc upstream.

We've seen this in a packet capture - I've intermixed what I
think was going on. The fix here is to grab the so_lock sooner.

1964379 -> #1 open (for write) reply seqid=1
1964393 -> #2 open (for read) reply seqid=2

__nfs4_close(), state->n_wronly--
nfs4_state_set_mode_locked(), changes state->state = [R]
state->flags is [RW]
state->state is [R], state->n_wronly == 0, state->n_rdonly == 1

1964398 -> #3 open (for write) call -> because close is already running
1964399 -> downgrade (to read) call seqid=2 (close of #1)
1964402 -> #3 open (for write) reply seqid=3

__update_open_stateid()
nfs_set_open_stateid_locked(), changes state->flags
state->flags is [RW]
state->state is [R], state->n_wronly == 0, state->n_rdonly == 1
new sequence number is exposed now via nfs4_stateid_copy()

next step would be update_open_stateflags(), pending so_lock

1964403 -> downgrade reply seqid=2, fails with OLD_STATEID (close of #1)

nfs4_close_prepare() gets so_lock and recalcs flags -> send close

1964405 -> downgrade (to read) call seqid=3 (close of #1 retry)

__update_open_stateid() gets so_lock
* update_open_stateflags() updates state->n_wronly.
nfs4_state_set_mode_locked() updates state->state

state->flags is [RW]
state->state is [RW], state->n_wronly == 1, state->n_rdonly == 1

* should have suppressed the preceding nfs4_close_prepare() from
sending open_downgrade

1964406 -> write call
1964408 -> downgrade (to read) reply seqid=4 (close of #1 retry)

nfs_clear_open_stateid_locked()
state->flags is [R]
state->state is [RW], state->n_wronly == 1, state->n_rdonly == 1

1964409 -> write reply (fails, openmode)

Signed-off-by: Andrew Elble <aweits@rit.edu>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/nfs/nfs4proc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -1385,6 +1385,7 @@ static void __update_open_stateid(struct
* Protect the call to nfs4_state_set_mode_locked and
* serialise the stateid update
*/
+ spin_lock(&state->owner->so_lock);
write_seqlock(&state->seqlock);
if (deleg_stateid != NULL) {
nfs4_stateid_copy(&state->stateid, deleg_stateid);
@@ -1393,7 +1394,6 @@ static void __update_open_stateid(struct
if (open_stateid != NULL)
nfs_set_open_stateid_locked(state, open_stateid, fmode);
write_sequnlock(&state->seqlock);
- spin_lock(&state->owner->so_lock);
update_open_stateflags(state, fmode);
spin_unlock(&state->owner->so_lock);
}