[PATCH] fuse: defer dentry_tree_work until fuse_dentry_tree_init()

[PATCH] fuse: defer dentry_tree_work until fuse_dentry_tree_init()

[Sang-Heon Jeon]

inval_wq_set() schedules dentry_tree_work when inval_wq is enabled.

But inval_wq_set() can be called at boot or module load before
fuse_dentry_tree_init() initializes the work, so __queue_delayed_work()
warns and the work never starts.

So defer scheduling the work until fuse_dentry_tree_init() sets it up.

Fixes: ab84ad597386 ("fuse: new work queue to periodically invalidate expired dentries")
Cc: stable@vger.kernel.org
Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
---
QEMU based test result
- booted with "fuse.inval_wq=5"

1) AS-IS (before fix)
[    0.011073] Kernel command line: rootwait root=/dev/vda console=tty1 console=ttyS0 nokaslr  fuse.inval_wq=5
[    0.011114] ------------[ cut here ]------------
[    0.011115] WARNING: kernel/workqueue.c:2704 at __queue_delayed_work+0x11a/0x140, CPU#0: swapper/0
[    0.011124] Modules linked in:
[    0.011128] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 7.4.0-rc1-00010-gab9787d7e66a #1 PREEMPT(undef) 
[    0.011130] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1ubuntu1 04/01/2014
[    0.011131] RIP: 0010:__queue_delayed_work+0x11a/0x140
[    0.011133] Code: c4 08 48 89 df 5b e9 85 28 0a 00 90 0f 0b 90 4c 8b 42 08 48 8d 42 08 49 39 c0 0f 84 1c ff ff ff 90 0f 0b 90 e9 13 ff ff ff 90 <0f> 0b 90 e9 ec fe ff ff bff
[    0.011134] RSP: 0000:ffffffff82e03e00 EFLAGS: 00010003 ORIG_RAX: 0000000000000000
[    0.011135] RAX: 0000000000000000 RBX: 0000000000000040 RCX: 0000000000001388
[    0.011136] RDX: ffffffff83a3f320 RSI: 0000000000000000 RDI: 0000000000000040
[    0.011136] RBP: 0000000000000000 R08: 0000000000000082 R09: 0000000000000001
[    0.011136] R10: 000000000000000a R11: 000000000000000a R12: ffffffff82c09fd0
[    0.011137] R13: ffff88807ffcfb89 R14: 0000000000000000 R15: 0000000000001388
[    0.011140] FS:  0000000000000000(0000) GS:ffff8880fa26e000(0000) knlGS:0000000000000000
[    0.011141] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.011141] CR2: ffff888003a67000 CR3: 0000000002e30000 CR4: 00000000000000b0
[    0.011142] Call Trace:
[    0.011143]  <TASK>
[    0.011143]  queue_delayed_work_on+0x6a/0x80
[    0.011145]  inval_wq_set+0xc4/0xe0
[    0.011149]  parse_args+0x299/0x3c0
[    0.011151]  ? __pfx_unknown_bootoption+0x10/0x10
[    0.011154]  start_kernel+0x3b8/0x7c0
[    0.011156]  ? __pfx_unknown_bootoption+0x10/0x10
[    0.011157]  x86_64_start_reservations+0x24/0x30
[    0.011160]  x86_64_start_kernel+0xd1/0xe0
[    0.011162]  common_startup_64+0x13e/0x158
[    0.011165]  </TASK>
[    0.011166] ---[ end trace 0000000000000000 ]---
[    0.011173] ------------[ cut here ]------------

2) TO-BE (after fix)
- no error while booting, and also fuse_dentry_tree_work works well.

---
 fs/fuse/dir.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index da23ccd8685c..6965a77a871f 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -39,6 +39,7 @@ static struct delayed_work dentry_tree_work;
 /* Minimum invalidation work queue frequency */
 #define FUSE_DENTRY_INVAL_FREQ_MIN 5
 
+static bool inval_wq_ready;
 unsigned __read_mostly inval_wq;
 static int inval_wq_set(const char *val, const struct kernel_param *kp)
 {
@@ -62,6 +63,10 @@ static int inval_wq_set(const char *val, const struct kernel_param *kp)
 
 	*((unsigned int *)kp->arg) = num;
 
+	/* Defer the work until fuse_dentry_tree_init() sets it up. */
+	if (!inval_wq_ready)
+		return 0;
+
 	if (num && !old)
 		schedule_delayed_work(&dentry_tree_work,
 				      secs_to_jiffies(num));
@@ -224,6 +229,11 @@ void fuse_dentry_tree_init(void)
 		dentry_hash[i].tree = RB_ROOT;
 	}
 	INIT_DELAYED_WORK(&dentry_tree_work, fuse_dentry_tree_work);
+	inval_wq_ready = true;
+
+	if (inval_wq)
+		schedule_delayed_work(&dentry_tree_work,
+				      secs_to_jiffies(inval_wq));
 }
 
 void fuse_dentry_tree_cleanup(void)

base-commit: ab9787d7e66ac7e6e94fc975b37c5b56fff98ca9
-- 
2.53.0