linux-kernel - Bisected regression in Linux 3.7.0-rc1, hang on login caused by replace

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Date:	Mon, 15 Oct 2012 17:14:37 -0400
From:	Pavel Roskin <proski@....org>
To:	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Bisected regression in Linux 3.7.0-rc1, hang on login caused by
 replace_fd()

Hello!

I tried the current mainline Linux on Fedora 16 x64_64 and found that I
cannot login in gdm.  I'm using gdm with LXDE.  After a few minutes,
kernel messages appear indicating a hung process gnome-settings-daemon.

Bisection found that the commit to blame is

commit 8280d16172243702ed43432f826ca6130edb4086
Author: Al Viro <viro@...iv.linux.org.uk>
Date:   Tue Aug 21 12:11:46 2012 -0400

    new helper: replace_fd()

    analog of dup2(), except that it takes struct file * as source.

    Signed-off-by: Al Viro <viro@...iv.linux.org.uk>

Reverting the part of the patch that changes fs/exec.c is sufficient to
fix the login behavior.

I was able to forward port the change to the current mainline Linux.
The call to replace_fd() was moved to fs/coredump.c, so the patch
changes it.  Also, it copies __clear_close_on_exec() and
__set_open_fd() from fs/file.c

The .config file, the kernel log and the forward ported patch are
attached.

I'll try to figure out why replace_fd() is not good in
umh_pipe_setup(), but I'd like to report the problem as soon as
possible, as it's very visible to the users and I don't want others to
spend hours bisecting it.

-- 
Regards,
Pavel Roskin

Download attachment "dotconfig" of type "application/octet-stream" (78210 bytes)

View attachment "kernel.log" of type "text/x-log" (194528 bytes)

View attachment "revert-replace_fd.patch" of type "text/x-patch" (2659 bytes)