Patchwork [2.6.31-rc4] gigaset: really fix chars_in_buffer

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Submitter Tilman Schmidt
Date Aug. 1, 2009, 12:18 p.m.
Message ID <20090801-patch-01.tilman@imap.cc>
Download mbox | patch
Permalink /patch/30454/
State Superseded
Delegated to: David Miller
Headers show

Comments

Tilman Schmidt - Aug. 1, 2009, 12:18 p.m.
This patch corrects the problem noted but left unfixed by commit
23198fda7182969b619613a555f8645fdc3dc334 "tty: fix chars_in_buffers".
The tty_operation chars_in_buffer() should return zero, not a
negative value, in the error case.

Impact: error handling bugfix
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
---

I only just noticed the "tty: fix chars_in_buffers" patch going in.
Please merge this follow-up fix for 2.6.31, too. Thanks.

 drivers/isdn/gigaset/interface.c |   18 +++++++-----------
 1 files changed, 7 insertions(+), 11 deletions(-)
Alan Cox - Aug. 1, 2009, 4:11 p.m.
On Sat,  1 Aug 2009 14:18:51 +0200 (CEST)
Tilman Schmidt <tilman@imap.cc> wrote:

> This patch corrects the problem noted but left unfixed by commit
> 23198fda7182969b619613a555f8645fdc3dc334 "tty: fix chars_in_buffers".
> The tty_operation chars_in_buffer() should return zero, not a
> negative value, in the error case.

Is that correct. If you take a signal so the mutex_lock_interruptible
takes the error path we'll exit any waits for characters to be flushed
from buffers and lose the bytes in some cases ? Thats why I didn't
convert it - I didn't understand why it was using _interruptible at all ?

Alan
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Tilman Schmidt - Aug. 1, 2009, 11:37 p.m.
Hi Alan,

thanks a lot for getting in contact with me, and for your
explanation of the rationale behind your patch.

On Sat, 1 Aug 2009 17:11:41 +0100, Alan Cox wrote:
> Is that correct. If you take a signal so the mutex_lock_interruptible
> takes the error path we'll exit any waits for characters to be flushed
> from buffers and lose the bytes in some cases ?

You are right. I'll have to change it to use non-interruptible
mutex_lock. I'll prepare a new patch.

> Thats why I didn't
> convert it - I didn't understand why it was using _interruptible at all ?

No specific reason. just the general rule to prefer sleeping
interuptibly whenever possible, because unkillable processes are
so annoying. Seeing that chars_in_buffer was declared as returning
int, I assumed (wrongly as it now turns out) that it would be
allowed to return the customary negative values for errors, so
that it could use the _interruptible variant. When I saw your
patch I read into it that zero would be the appropriate return
value for all error cases, including a signal while waiting for
the mutex. I guess there was a bit of wishful thinking in that.

Well, thanks again for your help. I'll follow up with a revised
patch.

Regards,
Tilman

Patch

diff --git a/drivers/isdn/gigaset/interface.c b/drivers/isdn/gigaset/interface.c
index 8b62df8..dfeec68 100644
--- a/drivers/isdn/gigaset/interface.c
+++ b/drivers/isdn/gigaset/interface.c
@@ -408,33 +408,29 @@  static int if_write_room(struct tty_struct *tty)
 	return retval;
 }
 
-/* FIXME: This function does not have error returns */
-
 static int if_chars_in_buffer(struct tty_struct *tty)
 {
 	struct cardstate *cs;
-	int retval = -ENODEV;
+	int retval = 0;
 
 	cs = (struct cardstate *) tty->driver_data;
 	if (!cs) {
 		pr_err("%s: no cardstate\n", __func__);
-		return -ENODEV;
+		return 0;
 	}
 
 	gig_dbg(DEBUG_IF, "%u: %s()", cs->minor_index, __func__);
 
 	if (mutex_lock_interruptible(&cs->mutex))
-		return -ERESTARTSYS; // FIXME -EINTR?
+		return 0;
 
-	if (!cs->connected) {
+	if (!cs->connected)
 		gig_dbg(DEBUG_IF, "not connected");
-		retval = -ENODEV;
-	} else if (!cs->open_count)
+	else if (!cs->open_count)
 		dev_warn(cs->dev, "%s: device not opened\n", __func__);
-	else if (cs->mstate != MS_LOCKED) {
+	else if (cs->mstate != MS_LOCKED)
 		dev_warn(cs->dev, "can't write to unlocked device\n");
-		retval = -EBUSY;
-	} else
+	else
 		retval = cs->ops->chars_in_buffer(cs);
 
 	mutex_unlock(&cs->mutex);