[PATCH] Put braces around potentially empty 'if' body in handle_pte_fault()

[PATCH] Put braces around potentially empty 'if' body in handle_pte_fault()

[Jesper Juhl]

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If one builds the kernel with -Wempty-body one gets this warning:

  mm/memory.c:3432:46: warning: suggest braces around empty body in an !ifc statement [-Wempty-body]

due to the fact that 'flush_tlb_fix_spurious_fault' is a macro that
can sometimes be defined to nothing.

I suggest we heed gcc's advice and put a pair of braces on that if.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
 mm/memory.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 829d437..9cf1b48 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3428,9 +3428,9 @@ int handle_pte_fault(struct mm_struct *mm,
 		 * This still avoids useless tlb flushes for .text page faults
 		 * with threads.
 		 */
-		if (flags & FAULT_FLAG_WRITE)
+		if (flags & FAULT_FLAG_WRITE) {
 			flush_tlb_fix_spurious_fault(vma, address);
+		}
 	}
 unlock:
 	pte_unmap_unlock(pte, ptl);
-- 
1.7.8

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Re: [PATCH] Put braces around potentially empty 'if' body in handle_pte_fault()

[Eric Dumazet]

Le dimanche 18 dA(C)cembre 2011 A  01:03 +0100, Jesper Juhl a A(C)crit :
> If one builds the kernel with -Wempty-body one gets this warning:
> 
>   mm/memory.c:3432:46: warning: suggest braces around empty body in an a??ifa?? statement [-Wempty-body]
> 
> due to the fact that 'flush_tlb_fix_spurious_fault' is a macro that
> can sometimes be defined to nothing.
> 
> I suggest we heed gcc's advice and put a pair of braces on that if.
> 
> Signed-off-by: Jesper Juhl <jj@chaosbits.net>
> ---
>  mm/memory.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 829d437..9cf1b48 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3428,9 +3428,9 @@ int handle_pte_fault(struct mm_struct *mm,
>  		 * This still avoids useless tlb flushes for .text page faults
>  		 * with threads.
>  		 */
> -		if (flags & FAULT_FLAG_WRITE)
> +		if (flags & FAULT_FLAG_WRITE) {
>  			flush_tlb_fix_spurious_fault(vma, address);
> +		}
>  	}
>  unlock:
>  	pte_unmap_unlock(pte, ptl);
> -- 
> 1.7.8
> 

Thats should be fixed in the reverse way :

#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)



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Re: [PATCH] Put braces around potentially empty 'if' body in handle_pte_fault()

[Jesper Juhl]

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On Sun, 18 Dec 2011, Eric Dumazet wrote:

> Le dimanche 18 dA(C)cembre 2011 A  01:03 +0100, Jesper Juhl a A(C)crit :
> > If one builds the kernel with -Wempty-body one gets this warning:
> > 
> >   mm/memory.c:3432:46: warning: suggest braces around empty body in an a??ifa?? statement [-Wempty-body]
> > 
> > due to the fact that 'flush_tlb_fix_spurious_fault' is a macro that
> > can sometimes be defined to nothing.
> > 
> > I suggest we heed gcc's advice and put a pair of braces on that if.
> > 
> > Signed-off-by: Jesper Juhl <jj@chaosbits.net>
> > ---
> >  mm/memory.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 829d437..9cf1b48 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -3428,9 +3428,9 @@ int handle_pte_fault(struct mm_struct *mm,
> >  		 * This still avoids useless tlb flushes for .text page faults
> >  		 * with threads.
> >  		 */
> > -		if (flags & FAULT_FLAG_WRITE)
> > +		if (flags & FAULT_FLAG_WRITE) {
> >  			flush_tlb_fix_spurious_fault(vma, address);
> > +		}
> >  	}
> >  unlock:
> >  	pte_unmap_unlock(pte, ptl);
> > -- 
> > 1.7.8
> > 
> 
> Thats should be fixed in the reverse way :
> 
> #define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
> 

I did consider that, bot opted for the other solution since there was only 
one user. But, on second thought, you are right, I should just have made 
the macro safe so that future uses also won't have problems. Will send a 
new patch in a minute.

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Re: [PATCH] Put braces around potentially empty 'if' body in handle_pte_fault()

[Al Viro]

On Sun, Dec 18, 2011 at 01:18:55AM +0100, Eric Dumazet wrote:
> Thats should be fixed in the reverse way :
> 
> #define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)

There's a better way to do that -
#define f(a) do { } while(0)
does not work as a function returning void -
	f(1), g();
won't work.  OTOH
#define f(a) ((void)0)
works just fine.

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Re: [PATCH] Put braces around potentially empty 'if' body in handle_pte_fault()

[Alexey Dobriyan]

On Sun, Dec 18, 2011 at 12:34:19AM +0000, Al Viro wrote:
> On Sun, Dec 18, 2011 at 01:18:55AM +0100, Eric Dumazet wrote:
> > Thats should be fixed in the reverse way :
> > 
> > #define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
> 
> There's a better way to do that -
> #define f(a) do { } while(0)
> does not work as a function returning void -
> 	f(1), g();
> won't work.  OTOH
> #define f(a) ((void)0)
> works just fine.

Two words: static inline.

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Re: [PATCH] Put braces around potentially empty 'if' body in handle_pte_fault()

[Andrew Morton]

On Sun, 18 Dec 2011 04:18:28 +0300
Alexey Dobriyan <adobriyan@gmail.com> wrote:

> On Sun, Dec 18, 2011 at 12:34:19AM +0000, Al Viro wrote:
> > On Sun, Dec 18, 2011 at 01:18:55AM +0100, Eric Dumazet wrote:
> > > Thats should be fixed in the reverse way :
> > > 
> > > #define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
> > 
> > There's a better way to do that -
> > #define f(a) do { } while(0)
> > does not work as a function returning void -
> > 	f(1), g();
> > won't work.  OTOH
> > #define f(a) ((void)0)
> > works just fine.
> 
> Two words: static inline.

Amen.  How often must we teach ourselves this lesson?


It gets a bit messy because of:

#ifndef flush_tlb_fix_spurious_fault
#define flush_tlb_fix_spurious_fault(vma, address) flush_tlb_page(vma, address)
#endif

But that can be handled with

static inline void flush_tlb_fix_spurious_fault(...)
{
	...
}
#define flush_tlb_fix_spurious_fault flush_tlb_fix_spurious_fault

and

#ifndef flush_tlb_fix_spurious_fault
static inline void flush_tlb_fix_spurious_fault(...)
{
}
#define flush_tlb_fix_spurious_fault flush_tlb_fix_spurious_fault
#endif

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