[PATCH] fuse: fix 'inval_wq' parameter setting during module initialisation

[Luis Henriques <luis@igalia.com>]

If the fuse module is loaded with a 'inval_wq' parameter the inval_wq_set()
function will schedule work into dentry_tree_work.  However this worker is
not initialised at this point because fuse_dentry_tree_init() will not have
been executed yet.

This can be fixed by delaying the work scheduling until later if the module
is still being initialised.

While there, also simplify the sched/cancel by using mod_delayed_work()
instead of schedule_delayed_work().  This will result in having the period
being changed immediately instead of waiting for the next reschedule.

Fixes: ab84ad597386 ("fuse: new work queue to periodically invalidate expired dentries")
Cc: stable@vger.kernel.org
Signed-off-by: Luis Henriques <luis@igalia.com>
---
Hi!

My initial approach to fix this was to use DECLARE_DELAYED_WORK() to
initialise the wq statically.  But this would then move the problem to
fuse_dentry_tree_work(), as the worker could still be scheduled before
the module finishes initialisation.

Cheers,
-- 
Luis

 fs/fuse/dir.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index e49b4e874b15..23c8259725c9 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -43,7 +43,6 @@ unsigned __read_mostly inval_wq;
 static int inval_wq_set(const char *val, const struct kernel_param *kp)
 {
 	unsigned int num;
-	unsigned int old = inval_wq;
 	int ret;
 
 	if (!val)
@@ -62,11 +61,14 @@ static int inval_wq_set(const char *val, const struct kernel_param *kp)
 
 	*((unsigned int *)kp->arg) = num;
 
-	if (num && !old)
-		schedule_delayed_work(&dentry_tree_work,
-				      secs_to_jiffies(num));
-	else if (!num && old)
-		cancel_delayed_work_sync(&dentry_tree_work);
+	/* Only start/stop workqueue if we're past module initialisation */
+	if (!module_is_coming(kp->mod)) {
+		if (num)
+			mod_delayed_work(system_percpu_wq, &dentry_tree_work,
+					 secs_to_jiffies(num));
+		else
+			cancel_delayed_work_sync(&dentry_tree_work);
+	}
 
 	return 0;
 }
@@ -224,6 +226,14 @@ void fuse_dentry_tree_init(void)
 		dentry_hash[i].tree = RB_ROOT;
 	}
 	INIT_DELAYED_WORK(&dentry_tree_work, fuse_dentry_tree_work);
+
+	/*
+	 * Start workqueue immediately if the module was loaded with the
+	 * 'inval_wq' parameter set
+	 */
+	if (inval_wq)
+		schedule_delayed_work(&dentry_tree_work,
+				      secs_to_jiffies(inval_wq));
 }
 
 void fuse_dentry_tree_cleanup(void)