From 322146d5d485cddb93761bd2593fbc932399b0a1 Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Fri, 9 Oct 2015 12:26:47 +0100 Subject: [PATCH] staging: comedi: don't poll_wait on same subdevice twice Comedi subdevices that support asynchronous acquisition commands have a wait queue head used for blocking reads or writes and for the poll file operation. The comedi device may have several subdevices that support "read" and/or "write" commands, but each open file object has at most one "read" subdevice and one "write" subdevice. It's possible (though rare) for those to be the same subdevice if the subdevice supports commands in either direction. In that case, the "poll" file operation doesn't really need to do a `poll_wait()` on the same subdevice twice. Although harmless, it wastes a poll table entry. Check for that, and avoid it. Signed-off-by: Ian Abbott Reviewed-by: H Hartley Sweeten Signed-off-by: Greg Kroah-Hartman --- drivers/staging/comedi/comedi_fops.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c index f341421f1644..bd124815c06a 100644 --- a/drivers/staging/comedi/comedi_fops.c +++ b/drivers/staging/comedi/comedi_fops.c @@ -2262,7 +2262,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait) unsigned int mask = 0; struct comedi_file *cfp = file->private_data; struct comedi_device *dev = cfp->dev; - struct comedi_subdevice *s; + struct comedi_subdevice *s, *s_read; mutex_lock(&dev->mutex); @@ -2272,6 +2272,7 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait) } s = comedi_file_read_subdevice(file); + s_read = s; if (s && s->async) { poll_wait(file, &s->async->wait_head, wait); if (!s->busy || !comedi_is_subdevice_running(s) || @@ -2284,7 +2285,8 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait) if (s && s->async) { unsigned int bps = comedi_bytes_per_sample(s); - poll_wait(file, &s->async->wait_head, wait); + if (s != s_read) + poll_wait(file, &s->async->wait_head, wait); comedi_buf_write_alloc(s, s->async->prealloc_bufsz); if (!s->busy || !comedi_is_subdevice_running(s) || !(s->async->cmd.flags & CMDF_WRITE) || -- 2.20.1