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 1913E4086A for ; Wed, 17 Sep 2025 13:25:46 +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=1758115547; cv=none; b=lD9dYJSE3SNbvtjy1wOtP1BHJgjDiG0+PoXP25OFjmA8iucboZd/SfbB+R1O9Mguvqu0bSDj4EMAlzaAnyWOrLtpQrTWTfLtd7o0GyUHiamugXsL/DNxiYRmvY9id/j+6jhHtH9uueGRb2nCf3lsWWu4RX287HHRlmjlwyfn4ec= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758115547; c=relaxed/simple; bh=a+lZ1t0PZfGKCrebKkzf23bf4UWWpao/AqNjkWkeNsY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jUEhScMYUuzxyQaLEbu8JXxAj/jyJbAX6bCP1R9HupUApNV65jNPkx45gmWYfRDhNKvgSE4kpcfem3iXYMklma2SFKl6YoMxiYQW3iyYiIJXtfnprsqpDph/3TD4QQexLtXAV7GtUTwpsV0DtzgfdbBC9Oq+0oOum/EV3jK8Xcw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DeOc+s7b; 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="DeOc+s7b" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9EEA5C4CEF5; Wed, 17 Sep 2025 13:25:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758115546; bh=a+lZ1t0PZfGKCrebKkzf23bf4UWWpao/AqNjkWkeNsY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DeOc+s7bi55Hh6yeEQ7+bJmS4JlRmRpckFTFrpQW6XxQoJvrYeKLTzHR1T3i77sfn vVFoEx9L/y1HOuBDNzIwV0N7uzvtFYFxisea03Jg7hriaLG0LbTm804O8M6BxrItyY Pmnk/SeAUEk+zfXkeuTVMd3fkTFHo+czAIi0jzsFc2VE324aREzQu5PURv7Kwk1jYa BFPTXRgg3eLo70qIn46Swit7lJQqKrslxONVfB2hEqUG/IldBLDSl7bfX155+9YeK1 6as0WsWVYIw/rj85T2zoQK4NEeeq0TkmAPuRKRyhFbIpw9pYbmlfO6fMFozGALv1GY V98SITUdhohDg== 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 5.10.y 2/2] USB: gadget: dummy-hcd: Fix locking bug in RT-enabled kernels Date: Wed, 17 Sep 2025 09:25:43 -0400 Message-ID: <20250917132543.548029-2-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250917132543.548029-1-sashal@kernel.org> References: <2025091724-unrivaled-crystal-942a@gregkh> <20250917132543.548029-1-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 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; } -- 2.51.0