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vcs: poll(): cope with a deallocated vt 

When VT_DISALLOCATE is used on a vt, user space waiting with poll() on
the corresponding /dev/vcs device is not awakened. This is now fixed by
returning POLLHUP|POLLERR to user space.

Also, in the normal screen update case, we don't set POLLERR anymore as
POLLPRI alone is a much more logical response in a non-error situation,
saving some confusion on the user space side. The only known user app
making use of poll() on /dev/vcs* is BRLTTY which is known to cope with
that change already, so the risk of breakage is pretty much nonexistent.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
hifive-unleashed-5.1
Nicolas Pitre 2019-01-08 22:55:03 -05:00 committed by Greg Kroah-Hartman
parent 8a08549431
commit 1bf931ab94
1 changed files with 15 additions and 6 deletions
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21
drivers/tty/vt/vc_screen.c
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@ -80,7 +80,7 @@
struct vcs_poll_data {
struct notifier_block notifier;
unsigned int cons_num;
bool seen_last_update;
int event;
wait_queue_head_t waitq;
struct fasync_struct *fasync;
};
@ -94,7 +94,7 @@ vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
container_of(nb, struct vcs_poll_data, notifier);
int currcons = poll->cons_num;
if (code != VT_UPDATE)
if (code != VT_UPDATE && code != VT_DEALLOCATE)
return NOTIFY_DONE;
if (currcons == 0)
@ -104,7 +104,7 @@ vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
if (currcons != vc->vc_num)
return NOTIFY_DONE;
poll->seen_last_update = false;
poll->event = code;
wake_up_interruptible(&poll->waitq);
kill_fasync(&poll->fasync, SIGIO, POLL_IN);
return NOTIFY_OK;
@ -261,7 +261,7 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
poll = file->private_data;
if (count && poll)
poll->seen_last_update = true;
poll->event = 0;
read = 0;
ret = 0;
while (count) {
@ -616,12 +616,21 @@ static __poll_t
vcs_poll(struct file *file, poll_table *wait)
{
struct vcs_poll_data *poll = vcs_poll_data_get(file);
__poll_t ret = DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
__poll_t ret = DEFAULT_POLLMASK|EPOLLERR;
if (poll) {
poll_wait(file, &poll->waitq, wait);
if (poll->seen_last_update)
switch (poll->event) {
case VT_UPDATE:
ret = DEFAULT_POLLMASK|EPOLLPRI;
break;
case VT_DEALLOCATE:
ret = DEFAULT_POLLMASK|EPOLLHUP|EPOLLERR;
break;
case 0:
ret = DEFAULT_POLLMASK;
break;
}
}
return ret;
}