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

Peter Hurley
2013-09-25T13:50:23Z

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@hurleysoftware.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@hurleysoftware.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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
>