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: [email protected] # v4.9.258
Signed-off-by: Xiaoming Ni <[email protected]>
---
kernel/futex.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
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:
--
2.27.0
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: [email protected] # v4.9.258
> Signed-off-by: Xiaoming Ni <[email protected]>
> ---
> 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 <[email protected]>
> 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
Follow Linaro: Facebook | Twitter | Blog
On Thu, Feb 25, 2021 at 09:17:38AM +0000, Lee Jones wrote:
> 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: [email protected] # v4.9.258
> > Signed-off-by: Xiaoming Ni <[email protected]>
> > ---
> > 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 <[email protected]>
Thanks, now queued up.
greg k-h