linux-kernel - [PATCH AUTOSEL 4.19 10/19] SUNRPC: increase size of rpc_wait_queue.qlen from unsigned short to unsigned int

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Message-ID: <20240329125100.3094358-10-sashal@kernel.org>
Date: Fri, 29 Mar 2024 08:50:42 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Dai Ngo <dai.ngo@...cle.com>,
	Jeff Layton <jlayton@...nel.org>,
	Trond Myklebust <trond.myklebust@...merspace.com>,
	Sasha Levin <sashal@...nel.org>,
	anna@...nel.org,
	chuck.lever@...cle.com,
	linux-nfs@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 10/19] SUNRPC: increase size of rpc_wait_queue.qlen from unsigned short to unsigned int

From: Dai Ngo <dai.ngo@...cle.com>

[ Upstream commit 2c35f43b5a4b9cdfaa6fdd946f5a212615dac8eb ]

When the NFS client is under extreme load the rpc_wait_queue.qlen counter
can be overflowed. Here is an instant of the backlog queue overflow in a
real world environment shown by drgn helper:

rpc_task_stats(rpc_clnt):
-------------------------
rpc_clnt: 0xffff92b65d2bae00
rpc_xprt: 0xffff9275db64f000
  Queue:  sending[64887] pending[524] backlog[30441] binding[0]
XMIT task: 0xffff925c6b1d8e98
     WRITE: 750654
        __dta_call_status_580: 65463
        __dta_call_transmit_status_579: 1
        call_reserveresult: 685189
        nfs_client_init_is_complete: 1
    COMMIT: 584
        call_reserveresult: 573
        __dta_call_status_580: 11
    ACCESS: 1
        __dta_call_status_580: 1
   GETATTR: 10
        __dta_call_status_580: 4
        call_reserveresult: 6
751249 tasks for server 111.222.333.444
Total tasks: 751249

count_rpc_wait_queues(xprt):
----------------------------
**** rpc_xprt: 0xffff9275db64f000 num_reqs: 65511
wait_queue: xprt_binding[0] cnt: 0
wait_queue: xprt_binding[1] cnt: 0
wait_queue: xprt_binding[2] cnt: 0
wait_queue: xprt_binding[3] cnt: 0
rpc_wait_queue[xprt_binding].qlen: 0 maxpriority: 0
wait_queue: xprt_sending[0] cnt: 0
wait_queue: xprt_sending[1] cnt: 64887
wait_queue: xprt_sending[2] cnt: 0
wait_queue: xprt_sending[3] cnt: 0
rpc_wait_queue[xprt_sending].qlen: 64887 maxpriority: 3
wait_queue: xprt_pending[0] cnt: 524
wait_queue: xprt_pending[1] cnt: 0
wait_queue: xprt_pending[2] cnt: 0
wait_queue: xprt_pending[3] cnt: 0
rpc_wait_queue[xprt_pending].qlen: 524 maxpriority: 0
wait_queue: xprt_backlog[0] cnt: 0
wait_queue: xprt_backlog[1] cnt: 685801
wait_queue: xprt_backlog[2] cnt: 0
wait_queue: xprt_backlog[3] cnt: 0
rpc_wait_queue[xprt_backlog].qlen: 30441 maxpriority: 3 [task cnt mismatch]

There is no effect on operations when this overflow occurs. However
it causes confusion when trying to diagnose the performance problem.

Signed-off-by: Dai Ngo <dai.ngo@...cle.com>
Reviewed-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: Trond Myklebust <trond.myklebust@...merspace.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/linux/sunrpc/sched.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
index 96837ae07822b..ca0a568fd8244 100644
--- a/include/linux/sunrpc/sched.h
+++ b/include/linux/sunrpc/sched.h
@@ -190,7 +190,7 @@ struct rpc_wait_queue {
 	unsigned char		maxpriority;		/* maximum priority (0 if queue is not a priority queue) */
 	unsigned char		priority;		/* current priority */
 	unsigned char		nr;			/* # tasks remaining for cookie */
-	unsigned short		qlen;			/* total # tasks waiting in queue */
+	unsigned int		qlen;			/* total # tasks waiting in queue */
 	struct rpc_timer	timer_list;
 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG) || IS_ENABLED(CONFIG_TRACEPOINTS)
 	const char *		name;
-- 
2.43.0