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
--- kernel/futex.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)
--- a/kernel/futex.c +++ b/kernel/futex.c @@ -1182,11 +1182,11 @@ static int handle_exit_race(u32 __user * 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);