Re: [PATCH] signal: Unexport sigsuspend()

From: Andrew Morton
Date: Wed Nov 18 2015 - 15:44:32 EST

On Mon, 16 Nov 2015 19:18:21 +0100 Richard Weinberger <richard@xxxxxx> wrote:

> 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.

So we don't know what caused this or when it started happening. hrm.
I guess I'll stick a cc:stable in there as it's likely to affect 4.3
and perhaps earlier, OK?

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