linux-kernel - [PATCH] n_tty: Fix poll() when TIME_CHAR and MIN

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Message-Id: <1392137400-4205-1-git-send-email-peter@hurleysoftware.com>
Date:	Tue, 11 Feb 2014 11:49:58 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>, Jiri Olsa <jolsa@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH] n_tty: Fix poll() when TIME_CHAR and MIN_CHAR == 0

On 02/11/2014 07:14 AM, Arnaldo Carvalho de Melo wrote:
> Em Mon, Feb 10, 2014 at 09:15:42PM -0500, Peter Hurley escreveu:
>>> Bisected it down to:
>
>>> eb3e4668bd9e0bbda592e830e889f137e44ec9e4 is the first bad commit
>>> Author: Peter Hurley <peter@...leysoftware.com>
>>> Date:   Mon Dec 2 14:24:42 2013 -0500
>
>>>      n_tty: Un-inline slow-path n_tty_receive_char()
>
>>> In a hurry now, will continue later, trying to understand what is the problem
>>> introduced by the above cset...
>
>>> Need to revert just this one to confirm that it is the culprit, etc.
>
>> Thanks for the report and bisect. Seems unlikely this commit is the
>> cause, but very likely to be some change I made since 3.13, since
>> I can repro on 3.14-rc1 but not on 3.13.2 -stable. I can also repro
>> this on 3.12 + the patch stack from me for 3.13 and 3.14.
>
>> I'm looking into this now.
>
> I just reverted just this cset and the problem persisted, so I'll wait
> for you on this one :-) 

My bisection pointed to:

eafbe67f84761d787802e5113d895a316b6292fe is the first bad commit
commit eafbe67f84761d787802e5113d895a316b6292fe
Author: Peter Hurley <peter@...leysoftware.com>
Date:   Mon Dec 2 14:24:45 2013 -0500

    n_tty: Refactor input_available_p() by call site

Apologies for the breakage; the patch below should fix it.

Regards,
Peter Hurley

--- >% ---
From: Peter Hurley <peter@...leysoftware.com>
Date: Tue, 11 Feb 2014 10:10:07 -0500
Subject: [PATCH] n_tty: Fix poll() when TIME_CHAR and MIN_CHAR == 0

Commit eafbe67f84761d787802e5113d895a316b6292fe,
  n_tty: Refactor input_available_p() by call site
broke poll() when TIME_CHAR(tty) and MIN_CHAR(tty) are both 0.

When TIME_CHAR and MIN_CHAR are both 0, input is available if the
read_cnt is 1 (not 0).

Reported-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/n_tty.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index cb8017a..2747a3b 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1896,7 +1896,7 @@ err:
 static inline int input_available_p(struct tty_struct *tty, int poll)
 {
 	struct n_tty_data *ldata = tty->disc_data;
-	int amt = poll && !TIME_CHAR(tty) ? MIN_CHAR(tty) : 1;
+	int amt = poll && !TIME_CHAR(tty) && MIN_CHAR(tty) ? MIN_CHAR(tty) : 1;
 
 	if (ldata->icanon && !L_EXTPROC(tty)) {
 		if (ldata->canon_head != ldata->read_tail)
-- 
1.8.1.2

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