Messages in this thread | | | Date | Thu, 26 Sep 2013 16:07:02 -0400 | From | Peter Hurley <> | Subject | 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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On 09/25/2013 09:52 AM, Peter Hurley wrote: > [ +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@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.)
Ok, I've managed to reproduce this (epic adventure).
What happens is the child process (the test) writes to its stdout (which is the slave end of a pty pair) and exits.
Then, the parent (expect), waiting for output from the child, is scheduled and run before the tty buffer i/o loop has pushed any data to the pty master read buffer.
IOW, at that particular instant, the pty appears to be closed (read return -EIO).
(The converse is also possible: ie., writing to the master and then closing the master may not be read by the slave.)
>>> Please consider reverting or fixing this patch.
I need to think a little on the right way to fix this.
Regards, Peter Hurley
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