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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/futex.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
--- a/kernel/futex.c +++ b/kernel/futex.c @@ -1909,12 +1909,13 @@ 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. */ free_pi_state(pi_state); pi_state = NULL; @@ -2580,12 +2581,13 @@ 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);