[PATCH v2] NFSv4: Fix a deadlock between nfs4_open_recover_helper() and delegreturn

[trondmy@kernel.org]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

If we're asked to recover open state while a delegation return is
outstanding, then the state manager thread cannot use a cached open, so
if the server returns a delegation, we can end up deadlocked behind the
pending delegreturn.
To avoid this problem, let's just ask the server not to give us a
delegation unless we're explicitly reclaiming one.

Fixes: be36e185bd26 ("NFSv4: nfs4_open_recover_helper() must set share access")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/nfs4proc.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index bd89c7f06952..e51044a5f550 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -2131,18 +2131,18 @@ static struct nfs4_opendata *nfs4_open_recoverdata_alloc(struct nfs_open_context
 }
 
 static int nfs4_open_recover_helper(struct nfs4_opendata *opendata,
-		fmode_t fmode)
+				    fmode_t fmode)
 {
 	struct nfs4_state *newstate;
+	struct nfs_server *server = NFS_SB(opendata->dentry->d_sb);
+	int openflags = opendata->o_arg.open_flags;
 	int ret;
 
 	if (!nfs4_mode_match_open_stateid(opendata->state, fmode))
 		return 0;
-	opendata->o_arg.open_flags = 0;
 	opendata->o_arg.fmode = fmode;
-	opendata->o_arg.share_access = nfs4_map_atomic_open_share(
-			NFS_SB(opendata->dentry->d_sb),
-			fmode, 0);
+	opendata->o_arg.share_access =
+		nfs4_map_atomic_open_share(server, fmode, openflags);
 	memset(&opendata->o_res, 0, sizeof(opendata->o_res));
 	memset(&opendata->c_res, 0, sizeof(opendata->c_res));
 	nfs4_init_opendata_res(opendata);
@@ -2724,10 +2724,15 @@ static int _nfs4_open_expired(struct nfs_open_context *ctx, struct nfs4_state *s
 	struct nfs4_opendata *opendata;
 	int ret;
 
-	opendata = nfs4_open_recoverdata_alloc(ctx, state,
-			NFS4_OPEN_CLAIM_FH);
+	opendata = nfs4_open_recoverdata_alloc(ctx, state, NFS4_OPEN_CLAIM_FH);
 	if (IS_ERR(opendata))
 		return PTR_ERR(opendata);
+	/*
+	 * We're not recovering a delegation, so ask for no delegation.
+	 * Otherwise the recovery thread could deadlock with an outstanding
+	 * delegation return.
+	 */
+	opendata->o_arg.open_flags = O_DIRECT;
 	ret = nfs4_open_recover(opendata, state);
 	if (ret == -ESTALE)
 		d_drop(ctx->dentry);
-- 
2.38.1