From ac31c7ff8624409ba3c4901df9237a616c187a5d Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 6 Nov 2019 22:55:45 +0100
Subject: [PATCH 10/11] futex: Provide distinct return value when owner is exiting
Git-commit: ac31c7ff8624409ba3c4901df9237a616c187a5d
Patch-mainline: v5.5-rc1
References: bsc#1149032
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: Davidlohr Bueso <dbueso@suse.de>
---
kernel/futex.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index 46a81e611065..4f9d7a4b6dbf 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1182,11 +1182,11 @@ static int handle_exit_race(u32 __user *uaddr, u32 uval,
u32 uval2;
/*
- * If the futex exit state is not yet FUTEX_STATE_DEAD, wait
- * for it to finish.
+ * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
+ * caller that the alleged owner is busy.
*/
if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
- return -EAGAIN;
+ return -EBUSY;
/*
* Reread the user space value to handle the following situation:
@@ -2092,12 +2092,13 @@ 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);
@@ -2843,12 +2844,13 @@ 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);
--
2.16.4