[PATCH] signal: Unexport sigsuspend()

From: Richard Weinberger
Date: Mon Nov 16 2015 - 13:18:44 EST

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. :-)

Reported-and-tested-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Signed-off-by: Richard Weinberger <richard@xxxxxx>
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 ab1e039..92557bb 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -239,7 +239,6 @@ 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 {
diff --git a/kernel/signal.c b/kernel/signal.c
index c0b01fe..f3f1f7a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3503,7 +3503,7 @@ SYSCALL_DEFINE0(pause)


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

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