From patchwork Fri Mar 15 17:06:33 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alan Stern X-Patchwork-Id: 13593797 Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by smtp.subspace.kernel.org (Postfix) with SMTP id 2F24C3A8E1 for ; Fri, 15 Mar 2024 17:06:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.131.102.5 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710522400; cv=none; b=fRl4GDTsCO7gCDa9EKb2S7YQQCnTHBYrRfIjnhXI6SQ9PEh4AwXpoagXV3OdZQUByMJjdTOna76X1V7ZSkMXM6CdH3wWjJmHvQwcAT/aAr/wpmlSBDQqQcouqI+NgYs7v+dmS6SrGowQOG9d49HVO7JuGvSIw+Eb430ZA3zqMlI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710522400; c=relaxed/simple; bh=OU8YWnHZFBpqGmHKHbqWjGFcwiWMPKRdz06JfTnuXuo=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=fPdpZ+1dvu+qEb+PqFjSPDx57rC+OvlRvWsB+3/GhQU9ydhiAJ/Rgs6bmRUluV3YxDQRQQKLz9vu33cVQTLAtmTELi43FTfRN2L033yUwcXwQMMqOmB7oC/rWI/o7CcgzoWqCGCeG5GmUH4xlOikQrMl5AcVJdvqWcBCSIh+bF0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=rowland.harvard.edu; spf=pass smtp.mailfrom=netrider.rowland.org; arc=none smtp.client-ip=192.131.102.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=rowland.harvard.edu Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=netrider.rowland.org Received: (qmail 492609 invoked by uid 1000); 15 Mar 2024 13:06:33 -0400 Date: Fri, 15 Mar 2024 13:06:33 -0400 From: Alan Stern To: Greg KH Cc: USB mailing list Subject: [PATCH 2/2] USB: core: Fix deadlock in port "disable" sysfs attribute Message-ID: Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <604da420-ae8a-4a9e-91a4-2d511ff404fb@rowland.harvard.edu> The show and store callback routines for the "disable" sysfs attribute file in port.c acquire the device lock for the port's parent hub device. This can cause problems if another process has locked the hub to remove it or change its configuration: Removing the hub or changing its configuration requires the hub interface to be removed, which requires the port device to be removed, and device_del() waits until all outstanding sysfs attribute callbacks for the ports have returned. The lock can't be released until then. But the disable_show() or disable_store() routine can't return until after it has acquired the lock. The resulting deadlock can be avoided by calling sysfs_break_active_protection(). This will cause the sysfs core not to wait for the attribute's callback routine to return, allowing the removal to proceed. The disadvantage is that after making this call, there is no guarantee that the hub structure won't be deallocated at any moment. To prevent this, we have to acquire a reference to it first by calling hub_get(). Signed-off-by: Alan Stern Cc: # Needs the previous patch in this series --- drivers/usb/core/port.c | 38 ++++++++++++++++++++++++++++++++++---- 1 file changed, 34 insertions(+), 4 deletions(-) Index: usb-devel/drivers/usb/core/port.c =================================================================== --- usb-devel.orig/drivers/usb/core/port.c +++ usb-devel/drivers/usb/core/port.c @@ -55,11 +55,22 @@ static ssize_t disable_show(struct devic u16 portstatus, unused; bool disabled; int rc; + struct kernfs_node *kn; + hub_get(hub); rc = usb_autopm_get_interface(intf); if (rc < 0) - return rc; + goto out_hub_get; + /* + * Prevent deadlock if another process is concurrently + * trying to unregister hdev. + */ + kn = sysfs_break_active_protection(&dev->kobj, &attr->attr); + if (!kn) { + rc = -ENODEV; + goto out_autopm; + } usb_lock_device(hdev); if (hub->disconnected) { rc = -ENODEV; @@ -69,9 +80,13 @@ static ssize_t disable_show(struct devic usb_hub_port_status(hub, port1, &portstatus, &unused); disabled = !usb_port_is_power_on(hub, portstatus); -out_hdev_lock: + out_hdev_lock: usb_unlock_device(hdev); + sysfs_unbreak_active_protection(kn); + out_autopm: usb_autopm_put_interface(intf); + out_hub_get: + hub_put(hub); if (rc) return rc; @@ -89,15 +104,26 @@ static ssize_t disable_store(struct devi int port1 = port_dev->portnum; bool disabled; int rc; + struct kernfs_node *kn; rc = kstrtobool(buf, &disabled); if (rc) return rc; + hub_get(hub); rc = usb_autopm_get_interface(intf); if (rc < 0) - return rc; + goto out_hub_get; + /* + * Prevent deadlock if another process is concurrently + * trying to unregister hdev. + */ + kn = sysfs_break_active_protection(&dev->kobj, &attr->attr); + if (!kn) { + rc = -ENODEV; + goto out_autopm; + } usb_lock_device(hdev); if (hub->disconnected) { rc = -ENODEV; @@ -118,9 +144,13 @@ static ssize_t disable_store(struct devi if (!rc) rc = count; -out_hdev_lock: + out_hdev_lock: usb_unlock_device(hdev); + sysfs_unbreak_active_protection(kn); + out_autopm: usb_autopm_put_interface(intf); + out_hub_get: + hub_put(hub); return rc; }