Messages in this thread Patch in this message | | | Date | Wed, 20 Nov 2019 09:38:24 -0000 | From | "tip-bot2 for Thomas Gleixner" <> | Subject | [tip: locking/core] futex: Provide distinct return value when owner is exiting |
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The following commit has been merged into the locking/core branch of tip:
Commit-ID: ac31c7ff8624409ba3c4901df9237a616c187a5d Gitweb: https://git.kernel.org/tip/ac31c7ff8624409ba3c4901df9237a616c187a5d Author: Thomas Gleixner <tglx@linutronix.de> AuthorDate: Wed, 06 Nov 2019 22:55:45 +01:00 Committer: Thomas Gleixner <tglx@linutronix.de> CommitterDate: Wed, 20 Nov 2019 09:40:10 +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);
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