Re: [PATCH] usb: gadget: f_fs: Remove WARN_ON in functionfs_bind

[Akash M/Akash M]

On 12/19/2024 6:22 PM, Akash M wrote:
> 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;
>   
Hi Greg,

I realized there's a minor nitpick with the patch I submitted - 
specifically a pair of extra brackets not removed.

Do you want me to proceed with sending a v2 to address this, or is this 
something you can take care while applying this patch?

Looking forward to your advice.

Thanks,
Akash