nfsd: Don't release the callback slot unless it was actually held
diff mbox series

Message ID 20190404025003.6143-1-trond.myklebust@hammerspace.com
State New
Headers show
Series
  • nfsd: Don't release the callback slot unless it was actually held
Related show

Commit Message

Trond Myklebust April 4, 2019, 2:50 a.m. UTC
If there are multiple callbacks queued, waiting for the callback
slot when the callback gets shut down, then they all currently
end up acting as if they hold the slot, and call
nfsd4_cb_sequence_done() resulting in interesting side-effects.

In addition, the 'retry_nowait' path in nfsd4_cb_sequence_done()
causes a loop back to nfsd4_cb_prepare() without first freeing the
slot, which causes a deadlock when nfsd41_cb_get_slot() gets called
a second time.

This patch therefore adds a boolean to track whether or not the
callback did pick up the slot, so that it can do the right thing
in these 2 cases.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfsd/nfs4callback.c | 8 +++++++-
 fs/nfsd/state.h        | 1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

Patch
diff mbox series

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index a1e79acb009f..8c61339eb063 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -939,8 +939,9 @@  static void nfsd4_cb_prepare(struct rpc_task *task, void *calldata)
 	cb->cb_seq_status = 1;
 	cb->cb_status = 0;
 	if (minorversion) {
-		if (!nfsd41_cb_get_slot(clp, task))
+		if (!cb->cb_holds_slot && !nfsd41_cb_get_slot(clp, task))
 			return;
+		cb->cb_holds_slot = true;
 	}
 	rpc_call_start(task);
 }
@@ -967,6 +968,9 @@  static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
 		return true;
 	}
 
+	if (!cb->cb_holds_slot)
+		return true;
+
 	switch (cb->cb_seq_status) {
 	case 0:
 		/*
@@ -1004,6 +1008,7 @@  static bool nfsd4_cb_sequence_done(struct rpc_task *task, struct nfsd4_callback
 			cb->cb_seq_status);
 	}
 
+	cb->cb_holds_slot = false;
 	clear_bit(0, &clp->cl_cb_slot_busy);
 	rpc_wake_up_next(&clp->cl_cb_waitq);
 	dprintk("%s: freed slot, new seqid=%d\n", __func__,
@@ -1211,6 +1216,7 @@  void nfsd4_init_cb(struct nfsd4_callback *cb, struct nfs4_client *clp,
 	cb->cb_seq_status = 1;
 	cb->cb_status = 0;
 	cb->cb_need_restart = false;
+	cb->cb_holds_slot = false;
 }
 
 void nfsd4_run_cb(struct nfsd4_callback *cb)
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 4673bb2dca03..5b944a959b49 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -70,6 +70,7 @@  struct nfsd4_callback {
 	int cb_seq_status;
 	int cb_status;
 	bool cb_need_restart;
+	bool cb_holds_slot;
 };
 
 struct nfsd4_callback_ops {