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-rw-r--r--kernel/futex.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index b766d28..3184d3b 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1781,13 +1781,14 @@ static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
*
* The basic logical guarantee of a futex is that it blocks ONLY
* if cond(var) is known to be true at the time of blocking, for
- * any cond. If we queued after testing *uaddr, that would open
- * a race condition where we could block indefinitely with
+ * any cond. If we locked the hash-bucket after testing *uaddr, that
+ * would open a race condition where we could block indefinitely with
* cond(var) false, which would violate the guarantee.
*
- * A consequence is that futex_wait() can return zero and absorb
- * a wakeup when *uaddr != val on entry to the syscall. This is
- * rare, but normal.
+ * On the other hand, we insert q and release the hash-bucket only
+ * after testing *uaddr. This guarantees that futex_wait() will NOT
+ * absorb a wakeup if *uaddr does not match the desired values
+ * while the syscall executes.
*/
retry:
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key);
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