Re: [PATCH 2/2] rtmutex: Reduce top-waiter blocking on a lock

[Davidlohr Bueso]

On Wed, 11 Apr 2018, kbuild test robot wrote:

> Hi Davidlohr,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on linus/master]
> [also build test WARNING on v4.16 next-20180411]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>
> url:    https://github.com/0day-ci/linux/commits/Davidlohr-Bueso/locking-rtmutex-Delete-save_state-member-of-struct-rt_mutex/20180411-155733
> reproduce:
>        # apt-get install sparse
>        make ARCH=x86_64 allmodconfig
>        make C=1 CF=-D__CHECK_ENDIAN__

Ok.

> sparse warnings: (new ones prefixed by >>)
>
> > > kernel/locking/rtmutex_common.h:62:9: sparse: context imbalance in '__rt_mutex_slowlock' - unexpected unlock

I did:

make C=1 CF=-D__CHECK_ENDIAN__ kernel/locking/rtmutex.o

But cannot trigger this message. There are however a ton of other
sparse issues with 'indirect_branch'. Ie:

./arch/x86/include/asm/nospec-branch.h:144:38: warning: Unknown escape '@'
./include/linux/init.h:134:6: error: attribute 'indirect_branch': unknown attribute
./include/linux/init.h:135:5: error: attribute 'indirect_branch': unknown attribute

More importantly, I don't follow where this "unexpected unlock" would come from
considering that rtmutex doesn't use __acquires/__releases annotations. Nor do
I understand why this patch would produce a new context imbalance.

Thanks,
Davidlohr