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")
Signed-off-by: Uttkarsh Aggarwal <quic_uaggarwa@xxxxxxxxxxx>
---
drivers/usb/gadget/function/f_fs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index a13c946e0663..f41a385a5c42 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -3535,6 +3535,7 @@ static void ffs_func_unbind(struct usb_configuration *c,
/* Drain any pending AIO completions */
drain_workqueue(ffs->io_completion_wq);
+ ffs_event_add(ffs, FUNCTIONFS_UNBIND);
if (!--opts->refcnt)
functionfs_unbind(ffs);
@@ -3559,7 +3560,6 @@ static void ffs_func_unbind(struct usb_configuration *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)
--
2.17.1
