This is a note to let you know that I've just added the patch titled
USB: usblp: fix a hang in poll() if disconnected
to my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.
The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.
If you have any questions about this process, please let me know.
From 7f6f181b3e2c4d08f5d693eebe7901a28fab8666 Mon Sep 17 00:00:00 2001
From: Pete Zaitcev zaitcev@redhat.com Date: Wed, 3 Mar 2021 22:10:53 -0600 Subject: USB: usblp: fix a hang in poll() if disconnected
Apparently an application that opens a device and calls select() on it, will hang if the decice is disconnected. It's a little surprising that we had this bug for 15 years, but apparently nobody ever uses select() with a printer: only write() and read(), and those work fine. Well, you can also select() with a timeout.
The fix is modeled after devio.c. A few other drivers check the condition first, then do not add the wait queue in case the device is disconnected. We doubt that's completely race-free. So, this patch adds the process first, then locks properly and checks for the disconnect.
Reviewed-by: Zqiang qiang.zhang@windriver.com Signed-off-by: Pete Zaitcev zaitcev@redhat.com Cc: stable stable@vger.kernel.org Link: https://lore.kernel.org/r/20210303221053.1cf3313e@suzdal.zaitcev.lan Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/class/usblp.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/drivers/usb/class/usblp.c b/drivers/usb/class/usblp.c index c9f6e9758288..f27b4aecff3d 100644 --- a/drivers/usb/class/usblp.c +++ b/drivers/usb/class/usblp.c @@ -494,16 +494,24 @@ static int usblp_release(struct inode *inode, struct file *file) /* No kernel lock - fine */ static __poll_t usblp_poll(struct file *file, struct poll_table_struct *wait) { - __poll_t ret; + struct usblp *usblp = file->private_data; + __poll_t ret = 0; unsigned long flags;
- struct usblp *usblp = file->private_data; /* Should we check file->f_mode & FMODE_WRITE before poll_wait()? */ poll_wait(file, &usblp->rwait, wait); poll_wait(file, &usblp->wwait, wait); + + mutex_lock(&usblp->mut); + if (!usblp->present) + ret |= EPOLLHUP; + mutex_unlock(&usblp->mut); + spin_lock_irqsave(&usblp->lock, flags); - ret = ((usblp->bidir && usblp->rcomplete) ? EPOLLIN | EPOLLRDNORM : 0) | - ((usblp->no_paper || usblp->wcomplete) ? EPOLLOUT | EPOLLWRNORM : 0); + if (usblp->bidir && usblp->rcomplete) + ret |= EPOLLIN | EPOLLRDNORM; + if (usblp->no_paper || usblp->wcomplete) + ret |= EPOLLOUT | EPOLLWRNORM; spin_unlock_irqrestore(&usblp->lock, flags); return ret; }