Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock

Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Davidlohr Bueso]

On Mon, 28 Oct 2019, Stefan Wahren wrote:

>Hi Davidlohr,
>
>Am 27.10.19 um 23:15 schrieb Davidlohr Bueso:
>> There seems no need to be using a semaphore, or a sleeping lock
>> in the first place: critical region is extremely short, does not
>> call into any blocking calls and furthermore lock and unlocking
>> operations occur in the same context.
>>
>> Get rid of another semaphore user by replacing it with a spinlock.
>>
>> Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
>> ---
>> This is in an effort to further reduce semaphore users in the kernel.
>>
>thanks for this. Could please also send this to devel@driverdev.osuosl.org?

Ccing.

>
>I only need to know, has this been tested on the Raspberry Pi?

No testing has been done, I have no hardware to test this.

Thanks,
Davidlohr
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Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Greg KH]

On Mon, Oct 28, 2019 at 08:21:08AM -0700, Davidlohr Bueso wrote:
> On Mon, 28 Oct 2019, Stefan Wahren wrote:
> 
> > Hi Davidlohr,
> > 
> > Am 27.10.19 um 23:15 schrieb Davidlohr Bueso:
> > > There seems no need to be using a semaphore, or a sleeping lock
> > > in the first place: critical region is extremely short, does not
> > > call into any blocking calls and furthermore lock and unlocking
> > > operations occur in the same context.
> > > 
> > > Get rid of another semaphore user by replacing it with a spinlock.
> > > 
> > > Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
> > > ---
> > > This is in an effort to further reduce semaphore users in the kernel.
> > > 
> > thanks for this. Could please also send this to devel@driverdev.osuosl.org?
> 
> Ccing.

I don't see a patch here :(

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Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Davidlohr Bueso]

Cc devel@driverdev.osuosl.org

On Sun, 27 Oct 2019, Bueso wrote:

>There seems no need to be using a semaphore, or a sleeping lock
>in the first place: critical region is extremely short, does not
>call into any blocking calls and furthermore lock and unlocking
>operations occur in the same context.
>
>Get rid of another semaphore user by replacing it with a spinlock.
>
>Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
>---
>This is in an effort to further reduce semaphore users in the kernel.
>
> .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
>diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
>index 8dc730cfe7a6..710d21654128 100644
>--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
>+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
>@@ -63,7 +63,7 @@ static char *g_free_fragments;
> static struct semaphore g_free_fragments_sema;
> static struct device *g_dev;
>
>-static DEFINE_SEMAPHORE(g_free_fragments_mutex);
>+static DEFINE_SPINLOCK(g_free_fragments_lock);
>
> static irqreturn_t
> vchiq_doorbell_irq(int irq, void *dev_id);
>@@ -528,11 +528,11 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
>
> 		WARN_ON(g_free_fragments == NULL);
>
>-		down(&g_free_fragments_mutex);
>+		spin_lock(&g_free_fragments_lock);
> 		fragments = g_free_fragments;
> 		WARN_ON(fragments == NULL);
> 		g_free_fragments = *(char **) g_free_fragments;
>-		up(&g_free_fragments_mutex);
>+		spin_unlock(&g_free_fragments_lock);
> 		pagelist->type = PAGELIST_READ_WITH_FRAGMENTS +
> 			(fragments - g_fragments_base) / g_fragments_size;
> 	}
>@@ -591,10 +591,10 @@ free_pagelist(struct vchiq_pagelist_info *pagelistinfo,
> 			kunmap(pages[num_pages - 1]);
> 		}
>
>-		down(&g_free_fragments_mutex);
>+		spin_lock(&g_free_fragments_lock);
> 		*(char **)fragments = g_free_fragments;
> 		g_free_fragments = fragments;
>-		up(&g_free_fragments_mutex);
>+		spin_unlock(&g_free_fragments_lock);
> 		up(&g_free_fragments_sema);
> 	}
>
>-- 
>2.16.4
>
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Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Greg KH]

On Mon, Oct 28, 2019 at 08:53:54AM -0700, Davidlohr Bueso wrote:
> Cc devel@driverdev.osuosl.org
> 
> On Sun, 27 Oct 2019, Bueso wrote:
> 
> > There seems no need to be using a semaphore, or a sleeping lock
> > in the first place: critical region is extremely short, does not
> > call into any blocking calls and furthermore lock and unlocking
> > operations occur in the same context.
> > 
> > Get rid of another semaphore user by replacing it with a spinlock.
> > 
> > Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
> > ---
> > This is in an effort to further reduce semaphore users in the kernel.
> > 
> > .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 +++++-----
> > 1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> > index 8dc730cfe7a6..710d21654128 100644
> > --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> > +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> > @@ -63,7 +63,7 @@ static char *g_free_fragments;
> > static struct semaphore g_free_fragments_sema;
> > static struct device *g_dev;
> > 
> > -static DEFINE_SEMAPHORE(g_free_fragments_mutex);
> > +static DEFINE_SPINLOCK(g_free_fragments_lock);
> > 
> > static irqreturn_t
> > vchiq_doorbell_irq(int irq, void *dev_id);
> > @@ -528,11 +528,11 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
> > 
> > 		WARN_ON(g_free_fragments == NULL);
> > 
> > -		down(&g_free_fragments_mutex);
> > +		spin_lock(&g_free_fragments_lock);
> > 		fragments = g_free_fragments;
> > 		WARN_ON(fragments == NULL);
> > 		g_free_fragments = *(char **) g_free_fragments;
> > -		up(&g_free_fragments_mutex);
> > +		spin_unlock(&g_free_fragments_lock);
> > 		pagelist->type = PAGELIST_READ_WITH_FRAGMENTS +
> > 			(fragments - g_fragments_base) / g_fragments_size;
> > 	}
> > @@ -591,10 +591,10 @@ free_pagelist(struct vchiq_pagelist_info *pagelistinfo,
> > 			kunmap(pages[num_pages - 1]);
> > 		}
> > 
> > -		down(&g_free_fragments_mutex);
> > +		spin_lock(&g_free_fragments_lock);
> > 		*(char **)fragments = g_free_fragments;
> > 		g_free_fragments = fragments;
> > -		up(&g_free_fragments_mutex);
> > +		spin_unlock(&g_free_fragments_lock);
> > 		up(&g_free_fragments_sema);
> > 	}
> > 
> > -- 
> > 2.16.4
> > 

This is obviously not in a format I can apply it in :(
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Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Davidlohr Bueso]

On Mon, 28 Oct 2019, Greg KH wrote:
>This is obviously not in a format I can apply it in :(

What are you talking about? I sent you the original patch,
then Cc'ed the drivers mailing list. So you still have a
patch you can apply... this is quite a common way of doing
things (Ccing for future references to someone or another
ml). I don't understand why you are hairsplitting over this
patch.

Thanks,
Davidlohr
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Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Greg KH]

On Mon, Oct 28, 2019 at 09:35:37AM -0700, Davidlohr Bueso wrote:
> On Mon, 28 Oct 2019, Greg KH wrote:
> > This is obviously not in a format I can apply it in :(
> 
> What are you talking about? I sent you the original patch,
> then Cc'ed the drivers mailing list. So you still have a
> patch you can apply... this is quite a common way of doing
> things (Ccing for future references to someone or another
> ml). I don't understand why you are hairsplitting over this
> patch.

I don't understand what is going on at all.  Is this patch already
applied?  If not, then yes, I need it in a format I can apply it in.  If
it's already applied to my tree/branch, then there's no need to send it
at all.

totally confused,

greg k-h
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Re: [PATCH] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Dan Carpenter]

On Mon, Oct 28, 2019 at 09:35:37AM -0700, Davidlohr Bueso wrote:
> On Mon, 28 Oct 2019, Greg KH wrote:
> > This is obviously not in a format I can apply it in :(
> 
> What are you talking about? I sent you the original patch,
> then Cc'ed the drivers mailing list.  So you still have a
> patch you can apply... this is quite a common way of doing
> things (Ccing for future references to someone or another
> ml). I don't understand why you are hairsplitting over this
> patch.
> 

I don't have the original patch either.  Only the corrupted one...  Maybe
you did it as html and it was rejected?

regards,
dan carpenter

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[PATCH resend] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Davidlohr Bueso]

There is no need to be using a semaphore, or a sleeping lock
in the first place: critical region is extremely short, does not
call into any blocking calls and furthermore lock and unlocking
operations occur in the same context.

Get rid of another semaphore user by replacing it with a spinlock.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
---
This is in an effort to further reduce semaphore users in the kernel.

This is a resend, which just seems simpler given the confusions.

 .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
index 8dc730cfe7a6..710d21654128 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
@@ -63,7 +63,7 @@ static char *g_free_fragments;
 static struct semaphore g_free_fragments_sema;
 static struct device *g_dev;
 
-static DEFINE_SEMAPHORE(g_free_fragments_mutex);
+static DEFINE_SPINLOCK(g_free_fragments_lock);
 
 static irqreturn_t
 vchiq_doorbell_irq(int irq, void *dev_id);
@@ -528,11 +528,11 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
 
 		WARN_ON(g_free_fragments == NULL);
 
-		down(&g_free_fragments_mutex);
+		spin_lock(&g_free_fragments_lock);
 		fragments = g_free_fragments;
 		WARN_ON(fragments == NULL);
 		g_free_fragments = *(char **) g_free_fragments;
-		up(&g_free_fragments_mutex);
+		spin_unlock(&g_free_fragments_lock);
 		pagelist->type = PAGELIST_READ_WITH_FRAGMENTS +
 			(fragments - g_fragments_base) / g_fragments_size;
 	}
@@ -591,10 +591,10 @@ free_pagelist(struct vchiq_pagelist_info *pagelistinfo,
 			kunmap(pages[num_pages - 1]);
 		}
 
-		down(&g_free_fragments_mutex);
+		spin_lock(&g_free_fragments_lock);
 		*(char **)fragments = g_free_fragments;
 		g_free_fragments = fragments;
-		up(&g_free_fragments_mutex);
+		spin_unlock(&g_free_fragments_lock);
 		up(&g_free_fragments_sema);
 	}
 
-- 
2.16.4

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Re: [PATCH resend] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Stefan Wahren]

Hi Davidlohr,

Am 01.11.19 um 19:29 schrieb Davidlohr Bueso:
> There is no need to be using a semaphore, or a sleeping lock
> in the first place: critical region is extremely short, does not
> call into any blocking calls and furthermore lock and unlocking
> operations occur in the same context.
>
> Get rid of another semaphore user by replacing it with a spinlock.
>
> Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
> ---
> This is in an effort to further reduce semaphore users in the kernel.
>
> This is a resend, which just seems simpler given the confusions.
>
>  .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> index 8dc730cfe7a6..710d21654128 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c
> @@ -63,7 +63,7 @@ static char *g_free_fragments;
>  static struct semaphore g_free_fragments_sema;
>  static struct device *g_dev;
>
> -static DEFINE_SEMAPHORE(g_free_fragments_mutex);
> +static DEFINE_SPINLOCK(g_free_fragments_lock);
>
>  static irqreturn_t
>  vchiq_doorbell_irq(int irq, void *dev_id);
> @@ -528,11 +528,11 @@ create_pagelist(char __user *buf, size_t count, unsigned short type)
>
>  		WARN_ON(g_free_fragments == NULL);
>
> -		down(&g_free_fragments_mutex);
> +		spin_lock(&g_free_fragments_lock);
>  		fragments = g_free_fragments;
>  		WARN_ON(fragments == NULL);
>  		g_free_fragments = *(char **) g_free_fragments;
> -		up(&g_free_fragments_mutex);
> +		spin_unlock(&g_free_fragments_lock);
>

the reason why Greg cannot apply this patch is that you are using an old
or the wrong git tree.

Please make sure you use the following one (or a mirror):

https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git

and operate on the branch staging-next

Please fix this up and send a new version.

Regards
Stefan


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Re: [PATCH resend] staging: vc04_services: replace g_free_fragments_mutex with spinlock

[Greg KH]

On Fri, Nov 01, 2019 at 11:29:49AM -0700, Davidlohr Bueso wrote:
> There is no need to be using a semaphore, or a sleeping lock
> in the first place: critical region is extremely short, does not
> call into any blocking calls and furthermore lock and unlocking
> operations occur in the same context.
> 
> Get rid of another semaphore user by replacing it with a spinlock.
> 
> Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
> ---
> This is in an effort to further reduce semaphore users in the kernel.
> 
> This is a resend, which just seems simpler given the confusions.
> 
>  .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)

This patch does not apply to my tree at all, what did you make it
against?

Please fix up and resend.

thanks,

greg k-h
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