Re: [PATCH] fuse: defer dentry_tree_work until fuse_dentry_tree_init()

[Luis Henriques <luis@igalia.com>]

On Wed, Nov 11 2026, Sang-Heon Jeon wrote:

> 2026년 11월 11일 (수) 오후 8:27, Sang-Heon Jeon <ekffu200098@gmail.com>님이 작성:
>>
>> Hi, Luis
>>
>> 2026년 11월 11일 (수) 오후 6:28, Luis Henriques <luis@igalia.com>님이 작성:
>> >
>> > On Wed, Nov 11 2026, Sang-Heon Jeon wrote:
>> >
>> > > 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"
>> >
>> > Thank you, Sang-Heon.  I've sent a fix for this already[1], but sashiko
>> > still has some race complains which I haven't looked into yet.  But maybe
>> > Miklos is happier with your patch, in which case you can add my
>>
>> Sorry, I missed that thread.. sashiko also complains about the same
>> race condition between init and sysfs setup. But I'm not sure it is a
>> realistic scenario. So I want to hear other voices as well.
>
> I also checked the other sashiko's complaints from your patch, the one
> about race between module cleanup and sysfs. It looks easier to
> reproduce, but still I'm not sure this is a realistic problem. If it
> is worth fixing, I will sent v2 with serialization between module
> init, cleanup and inval_wq_set()

I agree that the first race doesn't look realistic, though it could be
fixed by adding an extra spinlock (which could protect both inval_wq and
dentry_tree_is_initialised).

The second race would be easier to fix by setting
dentry_tree_is_initialised back to 'false' in fuse_dentry_tree_cleanup().

One thing I like with my version of the fix is that it replaces the usage
of schedule_delayed_work() by mod_delayed_work().  But maybe that's out
of the scope of this fix, and I should send that separately.

Cheers,
-- 
Luís


>> > Reviewed-by: Luis Henriques <luis@igalia.com>
>>
>> Thanks for your review :)
>>
>> > [1] https://lore.kernel.org/20261106155512.24801-1-luis%40igalia.com
>> >
>> > Cheers,
>> > --
>> > Luís
>> >
>> > > 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
>> > >
>> >
>>
>> Best regards,
>> Sang-Heon Jeon