futex: catch certain assymetric (get|put)_futex_key calls

Impact: add debug check

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@us.ibm.com>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 4 insertions, 1 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index c5ac55cc0c16..206d4c906885 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_ONCE(1);
                 return;
+        }
 
         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
         case FUT_OFF_INODE: