From: Uttkarsh Aggarwal quic_uaggarwa@quicinc.com
commit efb6b535207395a5c7317993602e2503ca8cb4b3 upstream.
While exercising the unbind path, with the current implementation the functionfs_unbind would be calling which waits for the ffs->mutex to be available, however within the same time ffs_ep0_read is invoked & if no setup packets are pending, it will invoke function wait_event_interruptible_exclusive_locked_irq which by definition waits for the ev.count to be increased inside the same mutex for which functionfs_unbind is waiting. This creates deadlock situation because the functionfs_unbind won't get the lock until ev.count is increased which can only happen if the caller ffs_func_unbind can proceed further.
Following is the illustration:
CPU1 CPU2
ffs_func_unbind() ffs_ep0_read() mutex_lock(ffs->mutex) wait_event(ffs->ev.count) functionfs_unbind() mutex_lock(ffs->mutex) mutex_unlock(ffs->mutex)
ffs_event_add()
<deadlock>
Fix this by moving the event unbind before functionfs_unbind to ensure the ev.count is incrased properly.
Fixes: 6a19da111057 ("usb: gadget: f_fs: Prevent race during ffs_ep0_queue_wait") Cc: stable stable@kernel.org Signed-off-by: Uttkarsh Aggarwal quic_uaggarwa@quicinc.com Link: https://lore.kernel.org/r/20230525092854.7992-1-quic_uaggarwa@quicinc.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/gadget/function/f_fs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -3620,6 +3620,7 @@ static void ffs_func_unbind(struct usb_c /* Drain any pending AIO completions */ drain_workqueue(ffs->io_completion_wq);
+ ffs_event_add(ffs, FUNCTIONFS_UNBIND); if (!--opts->refcnt) functionfs_unbind(ffs);
@@ -3644,7 +3645,6 @@ static void ffs_func_unbind(struct usb_c func->function.ssp_descriptors = NULL; func->interfaces_nums = NULL;
- ffs_event_add(ffs, FUNCTIONFS_UNBIND); }
static struct usb_function *ffs_alloc(struct usb_function_instance *fi)