linux-kernel - [PATCH 3.4 054/146] nfs: fix high load average due to callback thread sleeping

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Date:	Tue, 15 Sep 2015 17:02:49 +0800
From:	lizf@...nel.org
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Jeff Layton <jlayton@...chiereds.net>,
	Jeff Layton <jeff.layton@...marydata.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 054/146] nfs: fix high load average due to callback thread sleeping

From: Jeff Layton <jlayton@...chiereds.net>

3.4.109-rc1 review patch.  If anyone has any objections, please let me know.

------------------


commit 5d05e54af3cdbb13cf19c557ff2184781b91a22c upstream.

Chuck pointed out a problem that crept in with commit 6ffa30d3f734 (nfs:
don't call blocking operations while !TASK_RUNNING). Linux counts tasks
in uninterruptible sleep against the load average, so this caused the
system's load average to be pinned at at least 1 when there was a
NFSv4.1+ mount active.

Not a huge problem, but it's probably worth fixing before we get too
many complaints about it. This patch converts the code back to use
TASK_INTERRUPTIBLE sleep, simply has it flush any signals on each loop
iteration. In practice no one should really be signalling this thread at
all, so I think this is reasonably safe.

With this change, there's also no need to game the hung task watchdog so
we can also convert the schedule_timeout call back to a normal schedule.

Reported-by: Chuck Lever <chuck.lever@...cle.com>
Signed-off-by: Jeff Layton <jeff.layton@...marydata.com>
Tested-by: Chuck Lever <chuck.lever@...cle.com>
Fixes: commit 6ffa30d3f734 (“nfs: don't call blocking . . .”)
Signed-off-by: Trond Myklebust <trond.myklebust@...marydata.com>
[lizf: Backported to 3.4: adjust context]
Signed-off-by: Zefan Li <lizefan@...wei.com>
---
 fs/nfs/callback.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 07c056c..0184e91 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -149,7 +149,7 @@ nfs41_callback_svc(void *vrqstp)
 	set_freezable();
 
 	while (!kthread_should_stop()) {
-		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_UNINTERRUPTIBLE);
+		prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE);
 		spin_lock_bh(&serv->sv_cb_lock);
 		if (!list_empty(&serv->sv_cb_list)) {
 			req = list_first_entry(&serv->sv_cb_list,
@@ -163,10 +163,10 @@ nfs41_callback_svc(void *vrqstp)
 				error);
 		} else {
 			spin_unlock_bh(&serv->sv_cb_lock);
-			/* schedule_timeout to game the hung task watchdog */
-			schedule_timeout(60 * HZ);
+			schedule();
 			finish_wait(&serv->sv_cb_waitq, &wq);
 		}
+		flush_signals(current);
 	}
 	return 0;
 }
-- 
1.9.1

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