linux-kernel - Re: [Patch v5] rwsem: fix rwsem_is

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Message-Id: <20091015164602.ac75126f.akpm@linux-foundation.org>
Date:	Thu, 15 Oct 2009 16:46:02 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Amerigo Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Ben Woodard <bwoodard@...l.gov>,
	David Howells <dhowells@...hat.com>,
	Brian Behlendorf <behlendorf1@...l.gov>
Subject: Re: [Patch v5] rwsem: fix rwsem_is_locked() bugs

On Wed, 14 Oct 2009 05:52:22 -0400
Amerigo Wang <amwang@...hat.com> wrote:

> --- a/include/linux/rwsem-spinlock.h
> +++ b/include/linux/rwsem-spinlock.h
> @@ -68,11 +68,9 @@ extern int __down_write_trylock(struct rw_semaphore *sem);
>  extern void __up_read(struct rw_semaphore *sem);
>  extern void __up_write(struct rw_semaphore *sem);
>  extern void __downgrade_write(struct rw_semaphore *sem);
> +extern int __rwsem_is_locked(struct rw_semaphore *sem);
>  
> -static inline int rwsem_is_locked(struct rw_semaphore *sem)
> -{
> -	return (sem->activity != 0);
> -}
> +#define rwsem_is_locked(sem) __rwsem_is_locked(sem)
>  
>  #endif /* __KERNEL__ */
>  #endif /* _LINUX_RWSEM_SPINLOCK_H */
> diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
> index 9df3ca5..7014306 100644
> --- a/lib/rwsem-spinlock.c
> +++ b/lib/rwsem-spinlock.c
> @@ -17,6 +17,19 @@ struct rwsem_waiter {
>  #define RWSEM_WAITING_FOR_WRITE	0x00000002
>  };
>  
> +int __rwsem_is_locked(struct rw_semaphore *sem)
> +{
> +	int ret = 1;
> +	unsigned long flags;
> +
> +	if (spin_trylock_irqsave(&sem->wait_lock, flags)) {
> +		ret = (sem->activity != 0);
> +		spin_unlock_irqrestore(&sem->wait_lock, flags);
> +	}
> +	return ret;
> +}
> +EXPORT_SYMBOL(__rwsem_is_locked);

Why the macro tricks?  Can we do

--- a/include/linux/rwsem-spinlock.h~rwsem-fix-rwsem_is_locked-bugs-fix
+++ a/include/linux/rwsem-spinlock.h
@@ -68,9 +68,7 @@ extern int __down_write_trylock(struct r
 extern void __up_read(struct rw_semaphore *sem);
 extern void __up_write(struct rw_semaphore *sem);
 extern void __downgrade_write(struct rw_semaphore *sem);
-extern int __rwsem_is_locked(struct rw_semaphore *sem);
-
-#define rwsem_is_locked(sem) __rwsem_is_locked(sem)
+extern int rwsem_is_locked(struct rw_semaphore *sem);
 
 #endif /* __KERNEL__ */
 #endif /* _LINUX_RWSEM_SPINLOCK_H */
--- a/lib/rwsem-spinlock.c~rwsem-fix-rwsem_is_locked-bugs-fix
+++ a/lib/rwsem-spinlock.c
@@ -17,7 +17,7 @@ struct rwsem_waiter {
 #define RWSEM_WAITING_FOR_WRITE	0x00000002
 };
 
-int __rwsem_is_locked(struct rw_semaphore *sem)
+int rwsem_is_locked(struct rw_semaphore *sem)
 {
 	int ret = 1;
 	unsigned long flags;
@@ -28,7 +28,7 @@ int __rwsem_is_locked(struct rw_semaphor
 	}
 	return ret;
 }
-EXPORT_SYMBOL(__rwsem_is_locked);
+EXPORT_SYMBOL(rwsem_is_locked);
 
 /*
  * initialise the semaphore
_

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