[PATCH] usb: gadget: f_fs: initialize reset_work at allocation time

[Tyler Baker <tyler.baker@oss.qualcomm.com>]

ffs_fs_kill_sb() unconditionally calls cancel_work_sync() on
ffs->reset_work when a functionfs instance is unmounted:

	ffs_data_reset(ffs);
	cancel_work_sync(&ffs->reset_work);

However ffs->reset_work is only ever initialized via INIT_WORK() in
ffs_func_set_alt() and ffs_func_disable(), and only on the
FFS_DEACTIVATED path. That state is reached solely by ffs_data_closed()
when the instance is mounted with the "no_disconnect" option, so for the
common case (no "no_disconnect", or mounted and unmounted without ever
being deactivated) reset_work is never initialized.

ffs_data_new() allocates the ffs_data with kzalloc_obj() and does not
initialize reset_work, and ffs_data_reset()/ffs_data_clear() do not touch
it either, so reset_work.func is left NULL. cancel_work_sync() on such a
work then trips the WARN_ON(!work->func) guard in __flush_work():

  WARNING: kernel/workqueue.c:4301 at __flush_work+0x330/0x360, CPU#3: umount
  Call trace:
   __flush_work
   cancel_work_sync
   ffs_fs_kill_sb [usb_f_fs]
   deactivate_locked_super
   deactivate_super
   cleanup_mnt
   __cleanup_mnt
   task_work_run
   exit_to_user_mode_loop
   el0_svc

On older kernels cancel_work_sync() on a zero-initialized work struct was
a silent no-op, which hid the missing initialization.

Initialize reset_work once in ffs_data_new() so it is always valid for
the lifetime of the ffs_data, and drop the now-redundant INIT_WORK()
calls from the two deactivation paths.

Fixes: 18d6b32fca38 ("usb: gadget: f_fs: add "no_disconnect" mode")
Cc: stable@vger.kernel.org
Signed-off-by: Tyler Baker <tyler.baker@oss.qualcomm.com>
Cc: Loic Poulain <loic.poulain@oss.qualcomm.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Cc: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
---
 drivers/usb/gadget/function/f_fs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 75912ce6ab55..1ee21e29ef73 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -288,6 +288,7 @@ static int ffs_acquire_dev(const char *dev_name, struct ffs_data *ffs_data);
 static void ffs_release_dev(struct ffs_dev *ffs_dev);
 static int ffs_ready(struct ffs_data *ffs);
 static void ffs_closed(struct ffs_data *ffs);
+static void ffs_reset_work(struct work_struct *work);
 
 /* Misc helper functions ****************************************************/
 
@@ -2221,6 +2222,7 @@ static struct ffs_data *ffs_data_new(const char *dev_name)
 	init_waitqueue_head(&ffs->ev.waitq);
 	init_waitqueue_head(&ffs->wait);
 	init_completion(&ffs->ep0req_completion);
+	INIT_WORK(&ffs->reset_work, ffs_reset_work);
 
 	/* XXX REVISIT need to update it in some places, or do we? */
 	ffs->ev.can_stall = 1;
@@ -3775,7 +3777,6 @@ static int ffs_func_set_alt(struct usb_function *f,
 	if (ffs->state == FFS_DEACTIVATED) {
 		ffs->state = FFS_CLOSING;
 		spin_unlock_irqrestore(&ffs->eps_lock, flags);
-		INIT_WORK(&ffs->reset_work, ffs_reset_work);
 		schedule_work(&ffs->reset_work);
 		return -ENODEV;
 	}
@@ -3806,7 +3807,6 @@ static void ffs_func_disable(struct usb_function *f)
 	if (ffs->state == FFS_DEACTIVATED) {
 		ffs->state = FFS_CLOSING;
 		spin_unlock_irqrestore(&ffs->eps_lock, flags);
-		INIT_WORK(&ffs->reset_work, ffs_reset_work);
 		schedule_work(&ffs->reset_work);
 		return;
 	}
-- 
2.43.0