On Wed, 24 Feb 2021, Xiaoming Ni wrote:
> The handle_exit_race() function is defined in commit 9c3f39860367
> ("futex: Cure exit race"), which never returns -EBUSY. This results
> in a small piece of dead code in the attach_to_pi_owner() function:
>
> int ret = handle_exit_race(uaddr, uval, p); /* Never return -EBUSY */
> ...
> if (ret == -EBUSY)
> *exiting = p; /* dead code */
>
> The return value -EBUSY is added to handle_exit_race() in upsteam
> commit ac31c7ff8624409 ("futex: Provide distinct return value when
> owner is exiting"). This commit was incorporated into v4.9.255, before
> the function handle_exit_race() was introduced, whitout Modify
> handle_exit_race().
>
> To fix dead code, extract the change of handle_exit_race() from
> commit ac31c7ff8624409 ("futex: Provide distinct return value when owner
> is exiting"), re-incorporated.
>
> Fixes: 9c3f39860367 ("futex: Cure exit race")
> Cc: stable@xxxxxxxxxxxxxxx # v4.9.258
> Signed-off-by: Xiaoming Ni <nixiaoming@xxxxxxxxxx>
> ---
> kernel/futex.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
To clarify, this is not a wholesale back-port from Mainline.
It takes the remaining functional snippet of:
ac31c7ff8624409 ("futex: Provide distinct return value when owner is exiting")
... and is the correct fix for this issue.
Reviewed-by: Lee Jones <lee.jones@xxxxxxxxxx>
> diff --git a/kernel/futex.c b/kernel/futex.c
> index b65dbb5d60bb..0fd785410150 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1207,11 +1207,11 @@ 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:
--
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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