[PATCH] futex: fix dead code in attach_to_pi_owner()

[PATCH] futex: fix dead code in attach_to_pi_owner()

[Xiaoming Ni]

From: Thomas Gleixner <tglx@linutronix.de>

The handle_exit_race() function is defined in commit c158b461306df82
 ("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: c158b461306df82 ("futex: Cure exit race")
Cc: stable@vger.kernel.org # 4.9.258-rc1
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
---
 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

Re: [PATCH] futex: fix dead code in attach_to_pi_owner()

[Greg KH]

On Mon, Feb 22, 2021 at 08:53:52PM +0800, Xiaoming Ni wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> The handle_exit_race() function is defined in commit c158b461306df82
>  ("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: c158b461306df82 ("futex: Cure exit race")
> Cc: stable@vger.kernel.org # 4.9.258-rc1
> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
> ---
>  kernel/futex.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

What is the git commit id of this patch in Linus's tree?

Also, what kernel tree(s) is this supposed to go to?

thanks,

greg k-h

Re: [PATCH] futex: fix dead code in attach_to_pi_owner()

[Xiaoming Ni]

On 2021/2/25 16:25, Greg KH wrote:
> On Mon, Feb 22, 2021 at 08:53:52PM +0800, Xiaoming Ni wrote:
>> From: Thomas Gleixner <tglx@linutronix.de>
>>
>> The handle_exit_race() function is defined in commit c158b461306df82
>>   ("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.
mainline:
ac31c7ff8624 futex: Provide distinct return value when owner is exiting

>>
>> Fixes: c158b461306df82 ("futex: Cure exit race")

stable linux-4.9.y
9c3f39860367 futex: Cure exit race
c27f392040e2 futex: Provide distinct return value when owner is exiting

>> Cc: stable@vger.kernel.org # 4.9.258-rc1
>> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
>> ---
>>   kernel/futex.c | 6 +++---
>>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> What is the git commit id of this patch in Linus's tree?
> 
> Also, what kernel tree(s) is this supposed to go to?
> 
> thanks,
> 
> greg k-h
> .
> 
Sorry, the commit id c158b461306df82 in the patch does not exist in the 
linux-stable repository.
The commit ID is from linux-stable-rc.

I corrected the commit id in a subsequent email, and added a branch 
label. 
https://lore.kernel.org/lkml/20210224100923.51315-1-nixiaoming@huawei.com/

Sorry, I forgot to use "--in-reply-to=" when I sent the update patch.

This issue occurs only in the linux-4.9.y branch v4.9.258

Thanks
xiaoming Ni

Re: [PATCH] futex: fix dead code in attach_to_pi_owner()

[Lee Jones]

On Thu, 25 Feb 2021, Xiaoming Ni wrote:

> On 2021/2/25 16:25, Greg KH wrote:
> > On Mon, Feb 22, 2021 at 08:53:52PM +0800, Xiaoming Ni wrote:
> > > From: Thomas Gleixner <tglx@linutronix.de>
> > > 
> > > The handle_exit_race() function is defined in commit c158b461306df82
> > >   ("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.
> mainline:
> ac31c7ff8624 futex: Provide distinct return value when owner is exiting
> 
> > > 
> > > Fixes: c158b461306df82 ("futex: Cure exit race")
> 
> stable linux-4.9.y
> 9c3f39860367 futex: Cure exit race
> c27f392040e2 futex: Provide distinct return value when owner is exiting
> 
> > > Cc: stable@vger.kernel.org # 4.9.258-rc1
> > > Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
> > > ---
> > >   kernel/futex.c | 6 +++---
> > >   1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > What is the git commit id of this patch in Linus's tree?
> > 
> > Also, what kernel tree(s) is this supposed to go to?
> > 
> > thanks,
> > 
> > greg k-h
> > .
> > 
> Sorry, the commit id c158b461306df82 in the patch does not exist in the
> linux-stable repository.
> The commit ID is from linux-stable-rc.
> 
> I corrected the commit id in a subsequent email, and added a branch label.
> https://lore.kernel.org/lkml/20210224100923.51315-1-nixiaoming@huawei.com/

Replied to the follow-up.

> Sorry, I forgot to use "--in-reply-to=" when I sent the update patch.
> 
> This issue occurs only in the linux-4.9.y branch v4.9.258

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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