From: Alan Stern stern@rowland.harvard.edu
[ Upstream commit 8d63c83d8eb922f6c316320f50c82fa88d099bea ]
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 stern@rowland.harvard.edu Cc: stable stable@kernel.org Fixes: b4dbda1a22d2 ("USB: dummy-hcd: disable interrupts during req->complete") Reported-by: Yunseong Kim ysk@kzalloc.com Closes: https://lore.kernel.org/linux-usb/5b337389-73b9-4ee4-a83e-7e82bf5af87a@kzalloc.com/ Reported-by: syzbot+8baacc4139f12fa77909@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-usb/68ac2411.050a0220.37038e.0087.GAE@google.com/ Tested-by: syzbot+8baacc4139f12fa77909@syzkaller.appspotmail.com CC: Sebastian Andrzej Siewior bigeasy@linutronix.de CC: stable@vger.kernel.org Reviewed-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Link: https://lore.kernel.org/r/bb192ae2-4eee-48ee-981f-3efdbbd0d8f0@rowland.harva... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/usb/gadget/udc/dummy_hcd.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/usb/gadget/udc/dummy_hcd.c b/drivers/usb/gadget/udc/dummy_hcd.c index 7ed83241cf69d..0852d231959ac 100644 --- a/drivers/usb/gadget/udc/dummy_hcd.c +++ b/drivers/usb/gadget/udc/dummy_hcd.c @@ -759,8 +759,7 @@ static int dummy_dequeue(struct usb_ep *_ep, struct usb_request *_req) if (!dum->driver) return -ESHUTDOWN;
- local_irq_save(flags); - spin_lock(&dum->lock); + spin_lock_irqsave(&dum->lock, flags); list_for_each_entry(iter, &ep->queue, queue) { if (&iter->req != _req) continue; @@ -770,15 +769,16 @@ static int dummy_dequeue(struct usb_ep *_ep, struct usb_request *_req) retval = 0; break; } - spin_unlock(&dum->lock);
if (retval == 0) { dev_dbg(udc_dev(dum), "dequeued req %p from %s, len %d buf %p\n", req, _ep->name, _req->length, _req->buf); + spin_unlock(&dum->lock); usb_gadget_giveback_request(_ep, _req); + spin_lock(&dum->lock); } - local_irq_restore(flags); + spin_unlock_irqrestore(&dum->lock, flags); return retval; }