linux-kernel - [PATCH] futex: fix shared futex operations on nommu

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Message-ID: <20160426010303.GA3706@brightrain.aerifal.cx>
Date:	Mon, 25 Apr 2016 21:03:03 -0400
From:	Rich Felker <dalias@...c.org>
To:	linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Davidlohr Bueso <dave@...olabs.net>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Greg Ungerer <gerg@...inux.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: [PATCH] futex: fix shared futex operations on nommu

The shared get_futex_key code does not work on nommu, but is not
needed anyway because it's impossible for a given backing to have
multiple distinct virtual addresses on nommu. Simply disable these
code paths by refraining from setting FLAG_SHARED when CONFIG_MMU is
not enabled.

Signed-off-by: Rich Felker <dalias@...c.org>
---
 kernel/futex.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index a5d2e74..ed6f475 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3131,8 +3131,10 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 	int cmd = op & FUTEX_CMD_MASK;
 	unsigned int flags = 0;
 
+#ifdef CONFIG_MMU
 	if (!(op & FUTEX_PRIVATE_FLAG))
 		flags |= FLAGS_SHARED;
+#endif
 
 	if (op & FUTEX_CLOCK_REALTIME) {
 		flags |= FLAGS_CLOCKRT;
-- 
2.8.1