USB: gadget: dummy-hcd: Fix locking bug in RT-enabled kernels

Yunseong Kim and the syzbot fuzzer both reported a problem in
RT-enabled kernels caused by the way dummy-hcd mixes interrupt
management and spin-locking.  The pattern was:

	local_irq_save(flags);
	spin_lock(&dum->lock);
	...
	spin_unlock(&dum->lock);
	...		// calls usb_gadget_giveback_request()
	local_irq_restore(flags);

The code was written this way because usb_gadget_giveback_request()
needs to be called with interrupts disabled and the private lock not
held.

While this pattern works fine in non-RT kernels, it's not good when RT
is enabled.  RT kernels handle spinlocks much like mutexes; in particular,
spin_lock() may sleep.  But sleeping is not allowed while local
interrupts are disabled.

To fix the problem, rewrite the code to conform to the pattern used
elsewhere in dummy-hcd and other UDC drivers:

	spin_lock_irqsave(&dum->lock, flags);
	...
	spin_unlock(&dum->lock);
	usb_gadget_giveback_request(...);
	spin_lock(&dum->lock);
	...
	spin_unlock_irqrestore(&dum->lock, flags);

This approach satisfies the RT requirements.

Signed-off-by: Alan Stern <[email protected]>
Cc: stable <[email protected]>
Fixes: b4dbda1a22d2 ("USB: dummy-hcd: disable interrupts during req->complete")
Reported-by: Yunseong Kim <[email protected]>
Closes: <https://lore.kernel.org/linux-usb/[email protected]/>
Reported-by: [email protected]
Closes: <https://lore.kernel.org/linux-usb/[email protected]/>
Tested-by: [email protected]
CC: Sebastian Andrzej Siewior <[email protected]>
CC: [email protected]
Reviewed-by: Sebastian Andrzej Siewior <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

0 files changed, 0 insertions, 0 deletions