linux-kernel - Re: [REGRESSION][BISECTED] 3.12-rc "n_tty: Don't wait for buffer work in read() loop" patch breaks gcc's testsuite

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Date:	Wed, 25 Sep 2013 09:52:33 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Mikael Pettersson <mikpelinux@...il.com>
CC:	linux-kernel@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [REGRESSION][BISECTED] 3.12-rc "n_tty: Don't wait for buffer
 work in read() loop" patch breaks gcc's testsuite

[ +cc Greg Kroah-Hartman ]

On 09/25/2013 09:50 AM, Peter Hurley wrote:
> On 09/25/2013 08:18 AM, Mikael Pettersson wrote:
>> With 3.12-rc[12] I see unexpected failures in gcc's Ada acats testsuite, e.g.
>>
>>                  === acats tests ===
>> FAIL:   a83009b
>> FAIL:   c37209a
>> FAIL:   c45531e
>> FAIL:   c45614a
>> FAIL:   c67005d
>> FAIL:   c730a01
>> FAIL:   c74302b
>> FAIL:   cc3004a
>> FAIL:   cd2a24j
>> FAIL:   cd2a53a
>> FAIL:   cxa3001
>> FAIL:   cxf3a07
>> FAIL:   cxf3a08
>>
>>                  === acats Summary ===
>> # of expected passes            2307
>> # of unexpected failures        13
>> Native configuration is x86_64-unknown-linux-gnu
>
> Thanks for the report.
> Would you please send me the acats.log file from a failed testsuite run with its
> matching screen output?
>
> Regards,
> Peter Hurley
>
>
>> The exact failures vary from run to run, but some failures always occur on my
>> x86_64 machines, and all three open gcc branches (trunk, 4.8, 4.7) are affected.
>> With a 3.11 kernel the acats testsuite is always clean.
>>
>> A bisection identified:
>>
>>  From f95499c3030fe1bfad57745f2db1959c5b43dca8 Mon Sep 17 00:00:00 2001
>> From: Peter Hurley <peter@...leysoftware.com>
>> Date: Sat, 15 Jun 2013 13:14:29 +0000
>> Subject: n_tty: Don't wait for buffer work in read() loop
>>
>> User-space read() can run concurrently with receiving from device;
>> waiting for receive_buf() to complete is not required.
>>
>> Signed-off-by: Peter Hurley <peter@...leysoftware.com>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> ---
>> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
>> index fe1c399..a6eea30 100644
>> --- a/drivers/tty/n_tty.c
>> +++ b/drivers/tty/n_tty.c
>> @@ -1724,7 +1724,6 @@ static inline int input_available_p(struct tty_struct *tty, int amt)
>>   {
>>          struct n_tty_data *ldata = tty->disc_data;
>>
>> -       tty_flush_to_ldisc(tty);
>>          if (ldata->icanon && !L_EXTPROC(tty)) {
>>                  if (ldata->canon_head != ldata->read_tail)
>>                          return 1;
>>
>> as the culprit.  Reverting that from 3.12-rc2 eliminates the acats failures
>> and brings the gcc testsuite results to what one gets with 3.11.
>>
>> I can't pretend to understand exactly what goes wrong, suffice it to say that
>> the gcc testsuite harness uses a combination of shell, expect, and tcl.  I
>> suspect ptys are also involved.
>>
>> To repeat, bootstrap a recent gcc 4.8 snapshot w/ ada in --enable-languages,
>> then run the test suite with "make -j6 -k check; make mail-report.log".
>> (Adjust -jN as appropriate, but -j6 is what I'm using on my quad-core i7s.)
>>
>> Please consider reverting or fixing this patch.
>>
>> /Mikael


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