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    SubjectRe: [PATCH] mm/memory.c: remove warning from an uninitialized spinlock. was: Re: 2.6.21-rc7-mm2
    On Thu, 26 Apr 2007 20:25:19 +0200
    Borislav Petkov <bbpetkov@yahoo.de> 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 <bbpetkov@yahoo.de>
    > ---
    >
    > 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) :
    _
    -
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