From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD24733C757 for ; Wed, 17 Sep 2025 13:17:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758115077; cv=none; b=YcA9h2qx9urUv9oCDg8Ke0jGS8FF2q+vHd/A51EOV6I71VJdXbcJBnZhz/2cvPblAMHcOSz/Y5f0K4jow7TZxokfwa04tsKargxDR32ZmDon7jI7S60o+3FPLQnDfnxlWTy83qONYQos6q6rnggxuvALGCvhJaPxy4XwE6yadmY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758115077; c=relaxed/simple; bh=PUXt8vBXCPyub2qjx2UsCcaREbhRawZTKfh4zVu35yY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SVFTmpaeyVzX6SrBni2R7z6CkA7S1BxVeoQseecjCzoq1nH8N485ztIVynR1Gj1zMtYI96QWVYJYi+b4uNCo58/kkyIg1srLtkE8NT2xAF0pdrsK7B1vXocLk1oLzv6czzDuRjmesvIpNuKDPe99E5NaMHRAwJF9xE82FBZd6GQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JGzSskIk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JGzSskIk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9D79C4CEF5; Wed, 17 Sep 2025 13:17:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758115077; bh=PUXt8vBXCPyub2qjx2UsCcaREbhRawZTKfh4zVu35yY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JGzSskIknLb8jtjv1/CvsTvYraXNvz8gJaHqH4QAlQR/YM9H5fvab9GIjQ6mK0fcJ tfuhxeZhN0Q5MjJTpXVCUr6Dk6rAv3BpRRlRKX0jtJ2e3vnWYcn+e60RgbNrYFhEUG mLM4epuVYiyYQ0JjWJS6xUTzqW1U+vIG6AGx8ZB9vcz4C5bKbNNBeQr8lkqYvus09h 8tM8vkDlb9hcUaB4SkOr0S2drpZ83oVqJNCWvoovV8izMIFPhY920CXwixxYZ2qLqA +ekGvU+zoSoM9GnAmgw9bIyT4dg07n9e8Y61bNVhWryiC8O6FDxrD1Via4R31D+LPv W43pOo2BNcr7A== From: Sasha Levin To: stable@vger.kernel.org Cc: Alan Stern , stable , Yunseong Kim , syzbot+8baacc4139f12fa77909@syzkaller.appspotmail.com, Sebastian Andrzej Siewior , Greg Kroah-Hartman , Sasha Levin Subject: [PATCH 5.15.y 2/2] USB: gadget: dummy-hcd: Fix locking bug in RT-enabled kernels Date: Wed, 17 Sep 2025 09:17:54 -0400 Message-ID: <20250917131754.542916-2-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250917131754.542916-1-sashal@kernel.org> References: <2025091723-stack-cargo-2b1d@gregkh> <20250917131754.542916-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Alan Stern [ 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 Cc: stable Fixes: b4dbda1a22d2 ("USB: dummy-hcd: disable interrupts during req->complete") Reported-by: Yunseong Kim Closes: Reported-by: syzbot+8baacc4139f12fa77909@syzkaller.appspotmail.com Closes: Tested-by: syzbot+8baacc4139f12fa77909@syzkaller.appspotmail.com CC: Sebastian Andrzej Siewior CC: stable@vger.kernel.org Reviewed-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/bb192ae2-4eee-48ee-981f-3efdbbd0d8f0@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- 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 35aec8e7fc735..da658d349c9c3 100644 --- a/drivers/usb/gadget/udc/dummy_hcd.c +++ b/drivers/usb/gadget/udc/dummy_hcd.c @@ -761,8 +761,7 @@ 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; @@ -772,15 +771,16 @@ 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; } -- 2.51.0