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[11/12] futex: Provide distinct return value when owner is exiting

Message ID 20210201151214.2193508-12-lee.jones@linaro.org
State New
Headers show
Series Futex back-port from v4.9 | expand

Commit Message

Lee Jones Feb. 1, 2021, 3:12 p.m. UTC 
From: Thomas Gleixner <tglx@linutronix.de>


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>

---
 kernel/futex.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

-- 
2.25.1
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Patch

diff --git a/kernel/futex.c b/kernel/futex.c
index d21b151216aa3..32d799b9bd205 100644
--- 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);