[RT PATCH] locking/rwsem-rt: Remove might_sleep() in __up_read()

[RT PATCH] locking/rwsem-rt: Remove might_sleep() in __up_read()

[Andrew Halaney]

There's no chance of sleeping here, the reader is giving up the
lock and possibly waking up the writer who is waiting on it.

Reported-by: Chunyu Hu <chuhu@redhat.com>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
---
Hello,

I ran into a warning caused by this, and I think the warning is
incorrect. Please let me know if I'm wrong!
I'm working off of linux-5.12.y-rt, but this applies cleanly to older
stable branches as well.

Thanks,
Andrew

 kernel/locking/rwsem-rt.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/locking/rwsem-rt.c b/kernel/locking/rwsem-rt.c
index 274172d5bb3a..b61edc4dcb73 100644
--- a/kernel/locking/rwsem-rt.c
+++ b/kernel/locking/rwsem-rt.c
@@ -198,7 +198,6 @@ void __up_read(struct rw_semaphore *sem)
 	if (!atomic_dec_and_test(&sem->readers))
 		return;
 
-	might_sleep();
 	raw_spin_lock_irq(&m->wait_lock);
 	/*
 	 * Wake the writer, i.e. the rtmutex owner. It might release the
-- 
2.30.2

Re: [RT PATCH] locking/rwsem-rt: Remove might_sleep() in __up_read()

[Andrew Halaney]

On Tue, Apr 06, 2021 at 05:19:52PM -0500, Andrew Halaney wrote:
> There's no chance of sleeping here, the reader is giving up the
> lock and possibly waking up the writer who is waiting on it.
> 
> Reported-by: Chunyu Hu <chuhu@redhat.com>
> Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
> ---
> Hello,
> 
> I ran into a warning caused by this, and I think the warning is
> incorrect. Please let me know if I'm wrong!
> I'm working off of linux-5.12.y-rt, but this applies cleanly to older
> stable branches as well.
> 
> Thanks,
> Andrew
> 
>  kernel/locking/rwsem-rt.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/kernel/locking/rwsem-rt.c b/kernel/locking/rwsem-rt.c
> index 274172d5bb3a..b61edc4dcb73 100644
> --- a/kernel/locking/rwsem-rt.c
> +++ b/kernel/locking/rwsem-rt.c
> @@ -198,7 +198,6 @@ void __up_read(struct rw_semaphore *sem)
>  	if (!atomic_dec_and_test(&sem->readers))
>  		return;
>  
> -	might_sleep();
>  	raw_spin_lock_irq(&m->wait_lock);
>  	/*
>  	 * Wake the writer, i.e. the rtmutex owner. It might release the
> -- 
> 2.30.2
> 

Just a gentle follow up, any feedback?

Thanks,
Andrew

Re: [RT PATCH] locking/rwsem-rt: Remove might_sleep() in __up_read()

[Thomas Gleixner]

On Mon, Apr 26 2021 at 11:42, Andrew Halaney wrote:
> On Tue, Apr 06, 2021 at 05:19:52PM -0500, Andrew Halaney wrote:
>> There's no chance of sleeping here, the reader is giving up the
>> lock and possibly waking up the writer who is waiting on it.
>> 
>> Reported-by: Chunyu Hu <chuhu@redhat.com>
>> Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
>> ---
>> Hello,
>> 
>> I ran into a warning caused by this, and I think the warning is
>> incorrect. Please let me know if I'm wrong!
>> I'm working off of linux-5.12.y-rt, but this applies cleanly to older
>> stable branches as well.
>> 
>> Thanks,
>> Andrew
>> 
>>  kernel/locking/rwsem-rt.c | 1 -
>>  1 file changed, 1 deletion(-)
>> 
>> diff --git a/kernel/locking/rwsem-rt.c b/kernel/locking/rwsem-rt.c
>> index 274172d5bb3a..b61edc4dcb73 100644
>> --- a/kernel/locking/rwsem-rt.c
>> +++ b/kernel/locking/rwsem-rt.c
>> @@ -198,7 +198,6 @@ void __up_read(struct rw_semaphore *sem)
>>  	if (!atomic_dec_and_test(&sem->readers))
>>  		return;
>>  
>> -	might_sleep();
>>  	raw_spin_lock_irq(&m->wait_lock);
>>  	/*
>>  	 * Wake the writer, i.e. the rtmutex owner. It might release the
>> -- 
>> 2.30.2
>
> Just a gentle follow up, any feedback?

Looks correct. Will go into the next rt-release.

Thanks,

        tglx

Re: [RT PATCH] locking/rwsem-rt: Remove might_sleep() in __up_read()

[Andrew Halaney]

On Mon, Apr 26, 2021 at 08:16:34PM +0200, Thomas Gleixner wrote:
> On Mon, Apr 26 2021 at 11:42, Andrew Halaney wrote:
> > On Tue, Apr 06, 2021 at 05:19:52PM -0500, Andrew Halaney wrote:
> >> There's no chance of sleeping here, the reader is giving up the
> >> lock and possibly waking up the writer who is waiting on it.
> >> 
> >> Reported-by: Chunyu Hu <chuhu@redhat.com>
> >> Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
> >> ---
> >> Hello,
> >> 
> >> I ran into a warning caused by this, and I think the warning is
> >> incorrect. Please let me know if I'm wrong!
> >> I'm working off of linux-5.12.y-rt, but this applies cleanly to older
> >> stable branches as well.
> >> 
> >> Thanks,
> >> Andrew
> >> 
> >>  kernel/locking/rwsem-rt.c | 1 -
> >>  1 file changed, 1 deletion(-)
> >> 
> >> diff --git a/kernel/locking/rwsem-rt.c b/kernel/locking/rwsem-rt.c
> >> index 274172d5bb3a..b61edc4dcb73 100644
> >> --- a/kernel/locking/rwsem-rt.c
> >> +++ b/kernel/locking/rwsem-rt.c
> >> @@ -198,7 +198,6 @@ void __up_read(struct rw_semaphore *sem)
> >>  	if (!atomic_dec_and_test(&sem->readers))
> >>  		return;
> >>  
> >> -	might_sleep();
> >>  	raw_spin_lock_irq(&m->wait_lock);
> >>  	/*
> >>  	 * Wake the writer, i.e. the rtmutex owner. It might release the
> >> -- 
> >> 2.30.2
> >
> > Just a gentle follow up, any feedback?
> 
> Looks correct. Will go into the next rt-release.
> 
> Thanks,
> 
>         tglx
> 

Hi Thomas,

I see a new release (v5.13-rt1) was created, and with it rwsem
was overhauled entirely making this patch pointless for linux-rt-devel.

That being said, it's a little unclear to me how RT only patches
make their way to the maintained branches over in linux-stable-rt.
I think it should be applied to:
 v4.9-rt
 v4.14-rt
 v4.19-rt
 v5.4-rt
 v5.10-rt
to remove the incorrect warning, unless those branches plan to backport
the latest RT patchset with the new rwsem implementation. Is there a
proper way for me signal that?

Thanks,
Andrew

Re: [RT PATCH] locking/rwsem-rt: Remove might_sleep() in __up_read()

[Thomas Gleixner]

Andrew,

On Thu, Jul 08 2021 at 14:51, Andrew Halaney wrote:

Cc+ stable-rt folks and leave context untrimmed.

> On Mon, Apr 26, 2021 at 08:16:34PM +0200, Thomas Gleixner wrote:
>> On Mon, Apr 26 2021 at 11:42, Andrew Halaney wrote:
>> > On Tue, Apr 06, 2021 at 05:19:52PM -0500, Andrew Halaney wrote:
>> >> There's no chance of sleeping here, the reader is giving up the
>> >> lock and possibly waking up the writer who is waiting on it.
>> >> 
>> >> Reported-by: Chunyu Hu <chuhu@redhat.com>
>> >> Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
>> >> ---
>> >> Hello,
>> >> 
>> >> I ran into a warning caused by this, and I think the warning is
>> >> incorrect. Please let me know if I'm wrong!
>> >> I'm working off of linux-5.12.y-rt, but this applies cleanly to older
>> >> stable branches as well.
>> >>
>> >> Thanks,
>> >> Andrew
>> >> 
>> >>  kernel/locking/rwsem-rt.c | 1 -
>> >>  1 file changed, 1 deletion(-)
>> >> 
>> >> diff --git a/kernel/locking/rwsem-rt.c b/kernel/locking/rwsem-rt.c
>> >> index 274172d5bb3a..b61edc4dcb73 100644
>> >> --- a/kernel/locking/rwsem-rt.c
>> >> +++ b/kernel/locking/rwsem-rt.c
>> >> @@ -198,7 +198,6 @@ void __up_read(struct rw_semaphore *sem)
>> >>  	if (!atomic_dec_and_test(&sem->readers))
>> >>  		return;
>> >>  
>> >> -	might_sleep();
>> >>  	raw_spin_lock_irq(&m->wait_lock);
>> >>  	/*
>> >>  	 * Wake the writer, i.e. the rtmutex owner. It might release the
>> >> -- 
>> >> 2.30.2
>> >
>> > Just a gentle follow up, any feedback?
>> 
>> Looks correct. Will go into the next rt-release.
>> 
>> Thanks,
>> 
>>         tglx
>> 
>
> Hi Thomas,
>
> I see a new release (v5.13-rt1) was created, and with it rwsem
> was overhauled entirely making this patch pointless for linux-rt-devel.
>
> That being said, it's a little unclear to me how RT only patches
> make their way to the maintained branches over in linux-stable-rt.
> I think it should be applied to:
>  v4.9-rt
>  v4.14-rt
>  v4.19-rt
>  v5.4-rt
>  v5.10-rt
> to remove the incorrect warning, unless those branches plan to backport
> the latest RT patchset with the new rwsem implementation. Is there a
> proper way for me signal that?

See Cc.

Thanks,

        tglx