This commit addresses an issue related to below kernel panic where
panic_on_warn is enabled. It is caused by the unnecessary use of WARN_ON
in functionsfs_bind, which easily leads to the following scenarios.
1.adb_write in adbd 2. UDC write via configfs
================= =====================
->usb_ffs_open_thread() ->UDC write
->open_functionfs() ->configfs_write_iter()
->adb_open() ->gadget_dev_desc_UDC_store()
->adb_write() ->usb_gadget_register_driver_owner
->driver_register()
->StartMonitor() ->bus_add_driver()
->adb_read() ->gadget_bind_driver()
<times-out without BIND event> ->configfs_composite_bind()
->usb_add_function()
->open_functionfs() ->ffs_func_bind()
->adb_open() ->functionfs_bind()
<ffs->state !=FFS_ACTIVE>
The adb_open, adb_read, and adb_write operations are invoked from the
daemon, but trying to bind the function is a process that is invoked by
UDC write through configfs, which opens up the possibility of a race
condition between the two paths. In this race scenario, the kernel panic
occurs due to the WARN_ON from functionfs_bind when panic_on_warn is
enabled. This commit fixes the kernel panic by removing the unnecessary
WARN_ON.
Kernel panic - not syncing: kernel: panic_on_warn set ...
[ 14.542395] Call trace:
[ 14.542464] ffs_func_bind+0x1c8/0x14a8
[ 14.542468] usb_add_function+0xcc/0x1f0
[ 14.542473] configfs_composite_bind+0x468/0x588
[ 14.542478] gadget_bind_driver+0x108/0x27c
[ 14.542483] really_probe+0x190/0x374
[ 14.542488] __driver_probe_device+0xa0/0x12c
[ 14.542492] driver_probe_device+0x3c/0x220
[ 14.542498] __driver_attach+0x11c/0x1fc
[ 14.542502] bus_for_each_dev+0x104/0x160
[ 14.542506] driver_attach+0x24/0x34
[ 14.542510] bus_add_driver+0x154/0x270
[ 14.542514] driver_register+0x68/0x104
[ 14.542518] usb_gadget_register_driver_owner+0x48/0xf4
[ 14.542523] gadget_dev_desc_UDC_store+0xf8/0x144
[ 14.542526] configfs_write_iter+0xf0/0x138
Fixes: ddf8abd25994 ("USB: f_fs: the FunctionFS driver")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Akash M <akash.m5@xxxxxxxxxxx>
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 2920f8000bbd..92c883440e02 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -2285,7 +2285,7 @@ static int functionfs_bind(struct ffs_data *ffs, struct usb_composite_dev *cdev)
struct usb_gadget_strings **lang;
int first_id;
- if (WARN_ON(ffs->state != FFS_ACTIVE
+ if ((ffs->state != FFS_ACTIVE
|| test_and_set_bit(FFS_FL_BOUND, &ffs->flags)))
return -EBADFD;
--
2.17.1
