futex: Provide distinct return value when owner is exiting

commit ac31c7ff8624409ba3c4901df9237a616c187a5d upstream.

attach_to_pi_owner() returns -EAGAIN for various cases:

 - Owner task is exiting
 - Futex value has changed

The caller drops the held locks (hash bucket, mmap_sem) and retries the
operation. In case of the owner task exiting this can result in a live
lock.

As a preparatory step for seperating those cases, provide a distinct return
value (EBUSY) for the owner exiting case.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20191106224556.935606117@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/futex.c b/kernel/futex.c
index d21b151216aa395e69e4c7e0df7e98843136386d..32d799b9bd2051e10a6a5ab7df364d50622095a6 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1909,12 +1909,13 @@ retry_private:
                        if (!ret)
                                goto retry;
                        goto out;
+               case -EBUSY:
                case -EAGAIN:
                        /*
                         * Two reasons for this:
-                        * - Owner is exiting and we just wait for the
+                        * - EBUSY: Owner is exiting and we just wait for the
                         *   exit to complete.
-                        * - The user space value changed.
+                        * - EAGAIN: The user space value changed.
                         */
                        free_pi_state(pi_state);
                        pi_state = NULL;
@@ -2580,12 +2581,13 @@ retry_private:
                        goto out_unlock_put_key;
                case -EFAULT:
                        goto uaddr_faulted;
+               case -EBUSY:
                case -EAGAIN:
                        /*
                         * Two reasons for this:
-                        * - Task is exiting and we just wait for the
+                        * - EBUSY: Task is exiting and we just wait for the
                         *   exit to complete.
-                        * - The user space value changed.
+                        * - EAGAIN: The user space value changed.
                         */
                        queue_unlock(hb);
                        put_futex_key(&q.key);