On Sun, Apr 29, 2007 at 12:48:37AM +0100, Andy Whitcroft wrote: > Andrew Morton wrote: > > On Thu, 26 Apr 2007 20:25:19 +0200 > > Borislav Petkov <[EMAIL PROTECTED]> wrote: > > > >> Remove build warning mm/memory.c:1491: warning: 'ptl' may be used > >> uninitialized in this function. > >> The spinlock pointer is assigned to null since it gets overwritten right > >> away in > >> pte_alloc_map_lock(). > >> > >> Signed-off-by: Borislav Petkov <[EMAIL PROTECTED]> > >> --- > >> > >> Index: linux-mm/mm/memory.c > >> =================================================================== > >> --- linux-mm.orig/mm/memory.c 2007-04-26 19:57:14.000000000 +0200 > >> +++ linux-mm/mm/memory.c 2007-04-26 20:00:30.000000000 +0200 > >> @@ -1488,7 +1488,7 @@ > >> pte_t *pte; > >> int err; > >> struct page *pmd_page; > >> - spinlock_t *ptl; > >> + spinlock_t *ptl = NULL; > >> > >> pte = (mm == &init_mm) ? > >> pte_alloc_kernel(pmd, addr) : > >> > > > > yes, I've been staring unhappily at this for some time. > > > > Your change adds seven bytes of text to this function for no runtime > > benefit, just to fix a build-time warning. It's a general problem. > > > > > > Often we just leave the warning in place and curse gcc each time it flies > > past. Sometimes the code can be restructured in a sensible fashion to > > avoid the warning; often it cannot. > > > > But I don't think I want to put up with a warning coming out of core MM all > > the time so let's go with the following silliness which adds no additional > > runtime cost. > > > > --- > > a/mm/memory.c~add-apply_to_page_range-which-applies-a-function-to-a-pte-range-fix > > +++ a/mm/memory.c > > @@ -1455,7 +1455,7 @@ static int apply_to_pte_range(struct mm_ > > pte_t *pte; > > int err; > > struct page *pmd_page; > > - spinlock_t *ptl; > > + spinlock_t *ptl = ptl; /* Suppress gcc warning */ > > > > pte = (mm == &init_mm) ? > > pte_alloc_kernel(pmd, addr) : > > _ > > > > Perhaps we should have some kind definition helper. > > #define suppress_unused(x) x = x > > spinlock_t *suppress_unused(ptl);
I like that idea, let's do that. However, Andrew's concern remains still valid about suppressing the suppression and thereby hiding real bugs. But hey, the use of such a macro is pretty straightforward and if we choose a suitable name for it stating the unitialized state of the variable, messing up stuff then and producing a faulty code out of it is pretty careless to begin with, IMVHO. Here's a patch: ----- From: Borislav Petkov <[EMAIL PROTECTED]> Introduce a macro for suppressing gcc from generating a warning about a probable unitialized state of a variable. Signed-off-by: Borislav Petkov <[EMAIL PROTECTED]> --- Index: linux-mm/include/linux/compiler.h =================================================================== --- linux-mm.orig/include/linux/compiler.h +++ linux-mm/include/linux/compiler.h @@ -109,6 +109,10 @@ extern int do_check_likely(struct likeli (typeof(ptr)) (__ptr + (off)); }) #endif +#ifndef unitialized_var +# define unitialized_var(x) x = x +#endif + #endif /* __KERNEL__ */ #endif /* __ASSEMBLY__ */ Index: linux-mm/mm/memory.c =================================================================== --- linux-mm.orig/mm/memory.c +++ linux-mm/mm/memory.c @@ -1488,7 +1488,7 @@ static int apply_to_pte_range(struct mm_ pte_t *pte; int err; struct page *pmd_page; - spinlock_t *ptl; + spinlock_t *unitialized_var(ptl); pte = (mm == &init_mm) ? pte_alloc_kernel(pmd, addr) : -- Regards/Gruß, Boris. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/