On Fri, 7 Sep 2012 09:57:10 +0900
Minchan Kim <minchan@xxxxxxxxxx> wrote:
> When I compiled today, I met following warning.
> Correct it.
>
> mm/memory.c: In function ___copy_page_range___:
> include/linux/mmu_notifier.h:235:38: warning: ___mmun_end___ may be used uninitialized in this function [-Wuninitialized]
> mm/memory.c:1043:16: note: ___mmun_end___ was declared here
> include/linux/mmu_notifier.h:235:38: warning: ___mmun_start___ may be used uninitialized in this function [-Wuninitialized]
> mm/memory.c:1042:16: note: ___mmun_start___ was declared here
> LD mm/built-in.o
>
> Cc: Sagi Grimberg <sagig@xxxxxxxxxxxx>
> Cc: Haggai Eran <haggaie@xxxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> mm/memory.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 10e9b38..d000449 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1039,8 +1039,8 @@ int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> unsigned long next;
> unsigned long addr = vma->vm_start;
> unsigned long end = vma->vm_end;
> - unsigned long mmun_start; /* For mmu_notifiers */
> - unsigned long mmun_end; /* For mmu_notifiers */
> + unsigned long uninitialized_var(mmun_start); /* For mmu_notifiers */
> + unsigned long uninitialized_var(mmun_end); /* For mmu_notifiers */
> int ret;
>
Well yes, but a) uninitialized_var is a bit ugly and has some potential
to hide real bugs and b) it's not completely obvious that
is_cow_mapping() is stable across those two calls.
I think a better approach is this:
--- a/mm/memory.c~mm-move-all-mmu-notifier-invocations-to-be-done-outside-the-pt-lock-fix-fix
+++ a/mm/memory.c
@@ -1041,6 +1041,7 @@ int copy_page_range(struct mm_struct *ds
unsigned long end = vma->vm_end;
unsigned long mmun_start; /* For mmu_notifiers */
unsigned long mmun_end; /* For mmu_notifiers */
+ bool is_cow;
int ret;
/*
@@ -1074,7 +1075,8 @@ int copy_page_range(struct mm_struct *ds
* parent mm. And a permission downgrade will only happen if
* is_cow_mapping() returns true.
*/
- if (is_cow_mapping(vma->vm_flags)) {
+ is_cow = is_cow_mapping(vma->vm_flags);
+ if (is_cow) {
mmun_start = addr;
mmun_end = end;
mmu_notifier_invalidate_range_start(src_mm, mmun_start,
@@ -1095,7 +1097,7 @@ int copy_page_range(struct mm_struct *ds
}
} while (dst_pgd++, src_pgd++, addr = next, addr != end);
- if (is_cow_mapping(vma->vm_flags))
+ if (is_cow)
mmu_notifier_invalidate_range_end(src_mm, mmun_start, mmun_end);
return ret;
}
Unfortunately, my (old) versions of gcc are so stupid that they *still*
generate the warning even when the code is as obviously correct as this :(
Can you please test it with your compiler?
We should use this patch anyway - it makes memory.o text 13 bytes smaller.
is_cow_mapping() should return bool.
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