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
