linux-kernel - [PATCH] writeback: Fix wakeup and logging timeouts for !DETECT_HUNG

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Message-ID: <20260131090724.4128443-1-chenhuacai@loongson.cn>
Date: Sat, 31 Jan 2026 17:07:24 +0800
From: Huacai Chen <chenhuacai@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>
Cc: Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org,
	Xuefeng Li <lixuefeng@...ngson.cn>,
	Julian Sun <sunjunchao@...edance.com>,
	linux-kernel@...r.kernel.org,
	Huacai Chen <chenhuacai@...ngson.cn>
Subject: [PATCH] writeback: Fix wakeup and logging timeouts for !DETECT_HUNG_TASK

Recent changes of fs-writeback cause such warnings if DETECT_HUNG_TASK
is not enabled:

INFO: The task sync:1342 has been waiting for writeback completion for more than 1 seconds.

The reason is sysctl_hung_task_timeout_secs is 0 when DETECT_HUNG_TASK
is not enabled, then it causes the warning message even if the writeback
lasts for only one second.

I believe the wakeup and logging is also useful for !DETECT_HUNG_TASK,
so I don't want to disable them completely. As DEFAULT_HUNG_TASK_TIMEOUT
is 120 seconds, so for the !DETECT_HUNG_TASK case let's use 120 seconds
instead of sysctl_hung_task_timeout_secs.

Fixes: 1888635532fb ("writeback: Wake up waiting tasks when finishing the writeback of a chunk.")
Fixes: d6e621590764 ("writeback: Add logging for slow writeback (exceeds sysctl_hung_task_timeout_secs)")
Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
---
 fs/fs-writeback.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5444fc706ac7..847e46f0e019 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -198,10 +198,15 @@ static void wb_queue_work(struct bdi_writeback *wb,
 
 static bool wb_wait_for_completion_cb(struct wb_completion *done)
 {
+#ifndef CONFIG_DETECT_HUNG_TASK
+	unsigned long hung_secs = 120;
+#else
+	unsigned long hung_secs = sysctl_hung_task_timeout_secs;
+#endif
 	unsigned long waited_secs = (jiffies - done->wait_start) / HZ;
 
 	done->progress_stamp = jiffies;
-	if (waited_secs > sysctl_hung_task_timeout_secs)
+	if (waited_secs > hung_secs)
 		pr_info("INFO: The task %s:%d has been waiting for writeback "
 			"completion for more than %lu seconds.",
 			current->comm, current->pid, waited_secs);
@@ -1947,6 +1952,11 @@ static long writeback_sb_inodes(struct super_block *sb,
 	long write_chunk;
 	long total_wrote = 0;  /* count both pages and inodes */
 	unsigned long dirtied_before = jiffies;
+#ifndef CONFIG_DETECT_HUNG_TASK
+	unsigned long hung_secs = 120;
+#else
+	unsigned long hung_secs = sysctl_hung_task_timeout_secs;
+#endif
 
 	if (work->for_kupdate)
 		dirtied_before = jiffies -
@@ -2031,8 +2041,7 @@ static long writeback_sb_inodes(struct super_block *sb,
 
 		/* Report progress to inform the hung task detector of the progress. */
 		if (work->done && work->done->progress_stamp &&
-		   (jiffies - work->done->progress_stamp) > HZ *
-		   sysctl_hung_task_timeout_secs / 2)
+		   (jiffies - work->done->progress_stamp) > HZ * hung_secs / 2)
 			wake_up_all(work->done->waitq);
 
 		wbc_detach_inode(&wbc);
-- 
2.47.3