lkml.org 
[lkml]   [2019]   [Nov]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip: locking/core] futex: Provide distinct return value when owner is exiting
The following commit has been merged into the locking/core branch of tip:

Commit-ID: 8d4da5b197dc2aa3d10d9f1246d02e33b8f17acc
Gitweb: https://git.kernel.org/tip/8d4da5b197dc2aa3d10d9f1246d02e33b8f17acc
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Wed, 06 Nov 2019 22:55:45 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 15 Nov 2019 19:10:54 +01:00

futex: Provide distinct return value when owner is exiting

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

---
kernel/futex.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 46a81e6..4f9d7a4 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 @@ 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.
*/
double_unlock_hb(hb1, hb2);
hb_waiters_dec(hb2);
@@ -2843,12 +2844,13 @@ 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);
\
 
 \ /
  Last update: 2019-11-15 19:21    [W:0.202 / U:0.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site