linux-kernel - [PATCH] nfsd: fix oops when reading pool

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Date: Mon, 17 Jun 2024 07:54:08 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Sourabh Jain <sourabhjain@...ux.ibm.com>, 
 Chuck Lever <chuck.lever@...cle.com>, Neil Brown <neilb@...e.de>, 
 Olga Kornievskaia <kolga@...app.com>, Dai Ngo <Dai.Ngo@...cle.com>, 
 Tom Talpey <tom@...pey.com>
Cc: Trond Myklebust <trond.myklebust@...merspace.com>, 
 Anna Schumaker <anna@...nel.org>, linux-nfs@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>
Subject: [PATCH] nfsd: fix oops when reading pool_stats before server is
 started

Sourbh reported an oops that is triggerable by trying to read the
pool_stats procfile before nfsd had been started. Move the check for a
NULL serv in svc_pool_stats_start above the mutex acquisition, and fix
the stop routine not to unlock the mutex if there is no serv yet.

Fixes: 7b207ccd9833 ("svc: don't hold reference for poolstats, only mutex.")
Reported-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 net/sunrpc/svc_xprt.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index d3735ab3e6d1..b757a8891813 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1422,12 +1422,13 @@ static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
 
 	dprintk("svc_pool_stats_start, *pidx=%u\n", pidx);
 
+	if (!si->serv)
+		return NULL;
+
 	mutex_lock(si->mutex);
 
 	if (!pidx)
 		return SEQ_START_TOKEN;
-	if (!si->serv)
-		return NULL;
 	return pidx > si->serv->sv_nrpools ? NULL
 		: &si->serv->sv_pools[pidx - 1];
 }
@@ -1459,7 +1460,8 @@ static void svc_pool_stats_stop(struct seq_file *m, void *p)
 {
 	struct svc_info *si = m->private;
 
-	mutex_unlock(si->mutex);
+	if (si->serv)
+		mutex_unlock(si->mutex);
 }
 
 static int svc_pool_stats_show(struct seq_file *m, void *p)

---
base-commit: 4ddfda417a50309f17aeb85f8d1a9a9efbc7d81c
change-id: 20240617-nfsd-next-8593f73544f5

Best regards,
-- 
Jeff Layton <jlayton@...nel.org>