[PATCH] rwlock_is_locked undefined for UP systems

[PATCH] rwlock_is_locked undefined for UP systems

[Prashanth T]

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Hi,
    I had to use rwlock_is_locked( ) with linux2.6 for kdb and noticed that
this routine to be undefined for UP.  I have attached the patch for 2.6.1
below to return 0 for rwlock_is_locked( ) on UP systems.
Please let me know.

Thanks
Prashanth





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diff -urN linux-2.6.1/include/linux/spinlock.h linux-2.6.1-rwlock-patch/include/linux/spinlock.h
--- linux-2.6.1/include/linux/spinlock.h	2004-01-09 12:29:33.000000000 +0530
+++ linux-2.6.1-rwlock-patch/include/linux/spinlock.h	2004-01-16 18:15:10.000000000 +0530
@@ -176,6 +176,7 @@
 #endif
 
 #define rwlock_init(lock)	do { (void)(lock); } while(0)
+#define rwlock_is_locked(lock)  ((void)(lock), 0)
 #define _raw_read_lock(lock)	do { (void)(lock); } while(0)
 #define _raw_read_unlock(lock)	do { (void)(lock); } while(0)
 #define _raw_write_lock(lock)	do { (void)(lock); } while(0)

Re: [PATCH] rwlock_is_locked undefined for UP systems

[Arjan van de Ven]

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On Fri, 2004-01-16 at 14:45, Prashanth T wrote:
> Hi,
>     I had to use rwlock_is_locked( ) with linux2.6 for kdb and noticed that
> this routine to be undefined for UP.  I have attached the patch for 2.6.1
> below to return 0 for rwlock_is_locked( ) on UP systems.
> Please let me know.

I consider any user of this on UP to be broken, just like UP use of
spin_is_locked() is always a bug..... better a compiletime bug than a
runtime bug I guess...

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Re: [PATCH] rwlock_is_locked undefined for UP systems

[Joe Thornber]

On Fri, Jan 16, 2004 at 02:55:50PM +0100, Arjan van de Ven wrote:
> On Fri, 2004-01-16 at 14:45, Prashanth T wrote:
> > Hi,
> >     I had to use rwlock_is_locked( ) with linux2.6 for kdb and noticed that
> > this routine to be undefined for UP.  I have attached the patch for 2.6.1
> > below to return 0 for rwlock_is_locked( ) on UP systems.
> > Please let me know.
> 
> I consider any user of this on UP to be broken, just like UP use of
> spin_is_locked() is always a bug..... better a compiletime bug than a
> runtime bug I guess...

Then maybe a #error explaining this is in order ?

- Joe

Re: [PATCH] rwlock_is_locked undefined for UP systems

[Nikita Danilov]

Joe Thornber writes:
 > On Fri, Jan 16, 2004 at 02:55:50PM +0100, Arjan van de Ven wrote:
 > > On Fri, 2004-01-16 at 14:45, Prashanth T wrote:
 > > > Hi,
 > > >     I had to use rwlock_is_locked( ) with linux2.6 for kdb and noticed that
 > > > this routine to be undefined for UP.  I have attached the patch for 2.6.1
 > > > below to return 0 for rwlock_is_locked( ) on UP systems.
 > > > Please let me know.
 > > 
 > > I consider any user of this on UP to be broken, just like UP use of
 > > spin_is_locked() is always a bug..... better a compiletime bug than a
 > > runtime bug I guess...
 > 
 > Then maybe a #error explaining this is in order ?

So, if there is a function

void foo_locked(struct bar *obj)
{
    /* check that we are called with obj's lock held */
    BUG_ON(!rwlock_is_locked(&obj->lock));
    /* proceed with obj. */
}

it should now be changed to the

void foo_locked(struct bar *obj)
{
#ifdef CONFIG_SMP
    BUG_ON(!rwlock_is_locked(&obj->lock));
#endif
    /* proceed with obj. */
}

?

 > 
 > - Joe
 > 

Nikita.

 > 

Re: [PATCH] rwlock_is_locked undefined for UP systems

[Mike Fedyk]

On Fri, Jan 16, 2004 at 06:14:06PM +0300, Nikita Danilov wrote:
> it should now be changed to the
> 
> void foo_locked(struct bar *obj)
> {
> #ifdef CONFIG_SMP
>     BUG_ON(!rwlock_is_locked(&obj->lock));
> #endif
>     /* proceed with obj. */
> }

You forgot preempt... ;)

Re: [PATCH] rwlock_is_locked undefined for UP systems

[Christoph Hellwig]

On Fri, Jan 16, 2004 at 07:15:11PM +0530, Prashanth T wrote:
> Hi,
>     I had to use rwlock_is_locked( ) with linux2.6 for kdb and noticed that
> this routine to be undefined for UP.  I have attached the patch for 2.6.1
> below to return 0 for rwlock_is_locked( ) on UP systems.
> Please let me know.

we don't implement spin_is_locked on UP either because there's no really
usefull return value.  The lock will never be taken on !SMP && !PREEMPT,
but OTOH it's also not needed, so any assert on will give false results.
And the assert is probably the only thing that the _is_locked routines
could used for sanely.

Re: [PATCH] rwlock_is_locked undefined for UP systems

[Prashanth T]

ok....I understand that rwlock_is_locked( ) is to be protected by
CONFIG_SMP.  But I was tempted when I saw spin_is_locked( )
to be returning zero for !SMP in include/linux/spinlock.h . 
Am I seeing something wrong here?

Christoph Hellwig wrote:

>On Fri, Jan 16, 2004 at 07:15:11PM +0530, Prashanth T wrote:
>  
>
>>Hi,
>>    I had to use rwlock_is_locked( ) with linux2.6 for kdb and noticed that
>>this routine to be undefined for UP.  I have attached the patch for 2.6.1
>>below to return 0 for rwlock_is_locked( ) on UP systems.
>>Please let me know.
>>    
>>
>
>we don't implement spin_is_locked on UP either because there's no really
>usefull return value.  The lock will never be taken on !SMP && !PREEMPT,
>but OTOH it's also not needed, so any assert on will give false results.
>And the assert is probably the only thing that the _is_locked routines
>could used for sanely.
>
>
>  
>