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[24.9.64.241]) by smtp.gmail.com with ESMTPSA id v5sm12552039ilu.19.2021.08.10.16.25.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Aug 2021 16:25:52 -0700 (PDT) Subject: Re: [PATCH v2] usbip: give back URBs for unsent unlink requests during cleanup To: Anirudh Rayabharam , Valentina Manea , Shuah Khan , Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, linux-usb@vger.kernel.org, syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com, Shuah Khan References: <20210806181335.2078-1-mail@anirudhrb.com> From: Shuah Khan Message-ID: <4aaf420d-e85e-212e-3bc4-a70e016de610@linuxfoundation.org> Date: Tue, 10 Aug 2021 17:25:51 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210806181335.2078-1-mail@anirudhrb.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On 8/6/21 12:13 PM, Anirudh Rayabharam wrote: > In vhci_device_unlink_cleanup(), the URBs for unsent unlink requests are > not given back. This sometimes causes usb_kill_urb to wait indefinitely > for that urb to be given back. syzbot has reported a hung task issue [1] > for this. > > To fix this, give back the urbs corresponding to unsent unlink requests > (unlink_tx list) similar to how urbs corresponding to unanswered unlink > requests (unlink_rx list) are given back. Since the code is almost the > same, extract it into a new function and call it for both unlink_rx and > unlink_tx lists. > Let's not do the refactor - let's first fix the problem and then the refactor. > [1]: https://syzkaller.appspot.com/bug?id=08f12df95ae7da69814e64eb5515d5a85ed06b76 > > Reported-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com > Tested-by: syzbot+74d6ef051d3d2eacf428@syzkaller.appspotmail.com > Signed-off-by: Anirudh Rayabharam > --- > > Changes in v2: > Use WARN_ON() instead of BUG() when unlink_list is neither unlink_tx nor > unlink_rx. > > v1: https://lore.kernel.org/lkml/20210806164015.25263-1-mail@anirudhrb.com/ > > --- > drivers/usb/usbip/vhci_hcd.c | 45 +++++++++++++++++++++++++----------- > 1 file changed, 32 insertions(+), 13 deletions(-) > > diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c > index 4ba6bcdaa8e9..67e638f4c455 100644 > --- a/drivers/usb/usbip/vhci_hcd.c > +++ b/drivers/usb/usbip/vhci_hcd.c > @@ -945,7 +945,8 @@ static int vhci_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status) > return 0; > } > > -static void vhci_device_unlink_cleanup(struct vhci_device *vdev) > +static void __vhci_cleanup_unlink_list(struct vhci_device *vdev, > + struct list_head *unlink_list) > { > struct vhci_hcd *vhci_hcd = vdev_to_vhci_hcd(vdev); > struct usb_hcd *hcd = vhci_hcd_to_hcd(vhci_hcd); > @@ -953,23 +954,23 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev) > struct vhci_unlink *unlink, *tmp; > unsigned long flags; > > + if (WARN(unlink_list != &vdev->unlink_tx > + && unlink_list != &vdev->unlink_rx, > + "Invalid list passed to __vhci_cleanup_unlink_list\n")) > + return; > + With this change, this will be only place unlink_rx is used without vdev->priv_lock hold? Please explain why this is safe. > spin_lock_irqsave(&vhci->lock, flags); > spin_lock(&vdev->priv_lock); > > - list_for_each_entry_safe(unlink, tmp, &vdev->unlink_tx, list) { > - pr_info("unlink cleanup tx %lu\n", unlink->unlink_seqnum); > - list_del(&unlink->list); > - kfree(unlink); > - } > - > - while (!list_empty(&vdev->unlink_rx)) { > + list_for_each_entry_safe(unlink, tmp, unlink_list, list) { > struct urb *urb; > > - unlink = list_first_entry(&vdev->unlink_rx, struct vhci_unlink, > - list); > - > - /* give back URB of unanswered unlink request */ > - pr_info("unlink cleanup rx %lu\n", unlink->unlink_seqnum); > + if (unlink_list == &vdev->unlink_tx) > + pr_info("unlink cleanup tx %lu\n", > + unlink->unlink_seqnum); > + else > + pr_info("unlink cleanup rx %lu\n", > + unlink->unlink_seqnum); > > urb = pickup_urb_and_free_priv(vdev, unlink->unlink_seqnum); > if (!urb) { > @@ -1001,6 +1002,24 @@ static void vhci_device_unlink_cleanup(struct vhci_device *vdev) > spin_unlock_irqrestore(&vhci->lock, flags); > } > > +static inline void vhci_cleanup_unlink_tx(struct vhci_device *vdev) > +{ > + __vhci_cleanup_unlink_list(vdev, &vdev->unlink_tx); With this change, this will be only place unlink_rx is used without vdev->priv_lock hold? Please explain why this is safe. > +} > + Is there a need for this layer? > +static inline void vhci_cleanup_unlink_rx(struct vhci_device *vdev) > +{ > + __vhci_cleanup_unlink_list(vdev, &vdev->unlink_rx); With this change, this will be only place unlink_rx is used without vdev->priv_lock hold? Please explain why this is safe. > +} > + Is there a need for this layer? > +static void vhci_device_unlink_cleanup(struct vhci_device *vdev) > +{ > + /* give back URBs of unsent unlink requests */ > + vhci_cleanup_unlink_tx(vdev); > + /* give back URBs of unanswered unlink requests */ > + vhci_cleanup_unlink_rx(vdev); > +} > + > /* > * The important thing is that only one context begins cleanup. > * This is why error handling and cleanup become simple. > thanks, -- Shuah