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@xxxxxxxxxxxxx>
Signed-off-by: Pete Zaitcev <zaitcev@xxxxxxxxxx>
---
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 fd87405adbed..9596e4279294 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;
}
