futex: Reorder sanity checks in futex_requeue()

No point in allocating memory when the input parameters are bogus.
Validate all parameters before proceeding.

Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.581789253@linutronix.de

diff --git a/kernel/futex.c b/kernel/futex.c
index 8d8bad5..a5232f6 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1934,13 +1934,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
                        return -EINVAL;
 
                /*
-                * requeue_pi requires a pi_state, try to allocate it now
-                * without any locks in case it fails.
-                */
-               if (refill_pi_state_cache())
-                       return -ENOMEM;
-
-               /*
                 * futex_requeue() allows the caller to define the number
                 * of waiters to wake up via the @nr_wake argument. With
                 * REQUEUE_PI, waking up more than one waiter is creating
@@ -1963,6 +1956,13 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
                 */
                if (nr_wake != 1)
                        return -EINVAL;
+
+               /*
+                * requeue_pi requires a pi_state, try to allocate it now
+                * without any locks in case it fails.
+                */
+               if (refill_pi_state_cache())
+                       return -ENOMEM;
        }
 
 retry: