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 620533081D2; Tue, 30 Sep 2025 15:14:57 +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=1759245297; cv=none; b=tQweAXlvJVSTuhz+vRbb1QkDLVBSIzV8+mIhoGXJofJJvfaFDQZVbAetcvglQONN8Cd/RbgLXuPGtaLOjKssOxkNV2qb8OTgasx5a5lAHVfBTwk1Skqg5VLNCFFJeqFm1MgEHlZg6zZt1iJ1vtVudJX92hjVkWLzE2NcqRL63BA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759245297; c=relaxed/simple; bh=I5isv2tjyKwEFhsRDeMCn4gBt9LFE8a0ep0vHwB5K8k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=D8T0nUx9Ttcj74hEiUUtYU5ZA+tUtg1cqROZCV5wgc7MqBORVxPJWjNazK8gK/RKY8jtmrLHO9X/ltncGiR3siPlEBXEydd4t7nMWwMJPua22SRkJlwV4gKaef29MIMyqW+iLDPNZ/QuE5ptWzv07gKqC60ow5Q5bMPRgpp4aTg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=p2NTYvrB; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="p2NTYvrB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE7F2C19425; Tue, 30 Sep 2025 15:14:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1759245297; bh=I5isv2tjyKwEFhsRDeMCn4gBt9LFE8a0ep0vHwB5K8k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=p2NTYvrBhbUYj9rHsfEjXI+EZQR5LxEgOAA1L56KkwAfv131wHG2QteE7yXYJaGgN EZ/qWXeivuRZW6Q1pBFHuq5A9tN2R5gaB6iyI41mQGqHm1UOZEb2ZXPSck8LAEs4nR bmL/aMH91Ayd/O0QcObCibmgQD0gbkZZYUbdmsas= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alan Stern , stable , Yunseong Kim , syzbot+8baacc4139f12fa77909@syzkaller.appspotmail.com, Sebastian Andrzej Siewior , Sasha Levin Subject: [PATCH 5.15 094/151] USB: gadget: dummy-hcd: Fix locking bug in RT-enabled kernels Date: Tue, 30 Sep 2025 16:47:04 +0200 Message-ID: <20250930143831.340009572@linuxfoundation.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250930143827.587035735@linuxfoundation.org> References: <20250930143827.587035735@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ 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 Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/udc/dummy_hcd.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- 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 * 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 * 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; }