linux-kernel - [PATCH] futex: add WARN_ON to catch certain assymetric (get|put)_futex

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Date:	Mon, 29 Dec 2008 19:43:21 -0800
From:	Darren Hart <dvhltc@...ibm.com>
To:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Cc:	Darren Hart <dvhltc@...ibm.com>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Rusty Russell" <rusty@....ibm.com>
Subject: [PATCH] futex: add WARN_ON to catch certain assymetric
	(get|put)_futex_key calls

Following up on my previous key reference accounting patches, this patch
will catch puts on keys that haven't been "got".  This won't catch nested
get/put mismatches though.

Build and boot tested, with minimal desktop activity and a run of the
open_posix_testsuite in LTP for testing.  No warnings logged.

Signed-off-by: Darren Hart <dvhltc@...ibm.com>
Cc: "Peter Zijlstra" <peterz@...radead.org>
Cc: "Thomas Gleixner" <tglx@...utronix.de>
Cc: "Rusty Russell" <rusty@....ibm.com>
---

 kernel/futex.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 748778a..5288acf 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -170,8 +170,11 @@ static void get_futex_key_refs(union futex_key *key)
  */
 static void drop_futex_key_refs(union futex_key *key)
 {
-	if (!key->both.ptr)
+	if (!key->both.ptr) {
+		/* If we're here then we tried to put a key we failed to get */
+		WARN_ON(1);
 		return;
+	}
 
 	switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
 	case FUT_OFF_INODE:

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