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

Message ID 20210201100143.2028618-12-lee.jones@linaro.org
State Superseded
Headers show
Series Futex back-port from v4.14 | expand

Commit Message

Lee Jones Feb. 1, 2021, 10:01 a.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 e7798ef3b4b71..cc4590d9fe645 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1918,12 +1918,13 @@  static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
 			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.
 			 */
 			double_unlock_hb(hb1, hb2);
 			hb_waiters_dec(hb2);
@@ -2615,12 +2616,13 @@  static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
 			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);