linux-kernel - [PATCH 3.12 007/142] kernel/signal.c: unexport sigsuspend()

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Message-Id: <562b5d5e87834bfad9fd7baa9d23fccc74fd41b0.1456308281.git.jslaby@suse.cz>
Date:	Wed, 24 Feb 2016 11:03:22 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Richard Weinberger <richard@....at>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 007/142] kernel/signal.c: unexport sigsuspend()

From: Richard Weinberger <richard@....at>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 9d8a765211335cfdad464b90fb19f546af5706ae upstream.

sigsuspend() is nowhere used except in signal.c itself, so we can mark it
static do not pollute the global namespace.

But this patch is more than a boring cleanup patch, it fixes a real issue
on UserModeLinux.  UML has a special console driver to display ttys using
xterm, or other terminal emulators, on the host side.  Vegard reported
that sometimes UML is unable to spawn a xterm and he's facing the
following warning:

  WARNING: CPU: 0 PID: 908 at include/linux/thread_info.h:128 sigsuspend+0xab/0xc0()

It turned out that this warning makes absolutely no sense as the UML
xterm code calls sigsuspend() on the host side, at least it tries.  But
as the kernel itself offers a sigsuspend() symbol the linker choose this
one instead of the glibc wrapper.  Interestingly this code used to work
since ever but always blocked signals on the wrong side.  Some recent
kernel change made the WARN_ON() trigger and uncovered the bug.

It is a wonderful example of how much works by chance on computers. :-)

Fixes: 68f3f16d9ad0f1 ("new helper: sigsuspend()")
Signed-off-by: Richard Weinberger <richard@....at>
Reported-by: Vegard Nossum <vegard.nossum@...cle.com>
Tested-by: Vegard Nossum <vegard.nossum@...cle.com>
Acked-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 include/linux/signal.h | 1 -
 kernel/signal.c        | 2 +-
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index 2ac423bdb676..53944e50e421 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -247,7 +247,6 @@ extern int sigprocmask(int, sigset_t *, sigset_t *);
 extern void set_current_blocked(sigset_t *);
 extern void __set_current_blocked(const sigset_t *);
 extern int show_unhandled_signals;
-extern int sigsuspend(sigset_t *);

 struct sigaction {
 #ifndef __ARCH_HAS_IRIX_SIGACTION
diff --git a/kernel/signal.c b/kernel/signal.c
index fca2decd695e..e99136208d7e 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3551,7 +3551,7 @@ SYSCALL_DEFINE0(pause)

 #endif

-int sigsuspend(sigset_t *set)
+static int sigsuspend(sigset_t *set)
 {
 	current->saved_sigmask = current->blocked;
 	set_current_blocked(set);
-- 
2.7.1