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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Ingo Molnar" <mingo@redhat.com>,
        "Steven Rostedt (VMware)" <rostedt@goodmis.org>,
        "Mikulas Patocka" <mpatocka@redhat.com>
Date:   Sun, 11 Nov 2018 19:49:05 +0000
Message-ID: <lsq.1541965745.762417190@decadent.org.uk>
Subject: [PATCH 3.16 114/366] branch-check: fix long->int truncation when
 profiling branches
In-Reply-To: <lsq.1541965744.387173642@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
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3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@redhat.com>

commit 2026d35741f2c3ece73c11eb7e4a15d7c2df9ebe upstream.

The function __builtin_expect returns long type (see the gcc
documentation), and so do macros likely and unlikely. Unfortunatelly, when
CONFIG_PROFILE_ANNOTATED_BRANCHES is selected, the macros likely and
unlikely expand to __branch_check__ and __branch_check__ truncates the
long type to int. This unintended truncation may cause bugs in various
kernel code (we found a bug in dm-writecache because of it), so it's
better to fix __branch_check__ to return long.

Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1805300818140.24812@file01.intranet.prod.int.rdu2.redhat.com

Cc: Ingo Molnar <mingo@redhat.com>
Fixes: 1f0d69a9fc815 ("tracing: profile likely and unlikely annotations")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 include/linux/compiler.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -105,7 +105,7 @@ void ftrace_likely_update(struct ftrace_
 #define unlikely_notrace(x)	__builtin_expect(!!(x), 0)
 
 #define __branch_check__(x, expect) ({					\
-			int ______r;					\
+			long ______r;					\
 			static struct ftrace_branch_data		\
 				__attribute__((__aligned__(4)))		\
 				__attribute__((section("_ftrace_annotated_branch"))) \