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SubjectRe: [PATCH] frontswap: fix incorrect zeroing and allocation size for frontswap_map
On Sun, Jun 02, 2013 at 08:52:57AM +0900, Akinobu Mita wrote:
> The bitmap accessed by bitops must have enough size to hold the required
> numbers of bits rounded up to a multiple of BITS_PER_LONG. And the bitmap
> must not be zeroed by memset() if the number of bits cleared is not
> a multiple of BITS_PER_LONG.
>
> This fixes incorrect zeroing and allocation size for frontswap_map.
> The incorrect zeroing part doesn't cause any problem because
> frontswap_map is freed just after zeroing. But the wrongly calculated
> allocation size may cause the problem.
>
> For 32bit systems, the allocation size of frontswap_map is about twice as
> large as required size. For 64bit systems, the allocation size is smaller
> than requeired if the number of bits is not a multiple of BITS_PER_LONG.
^^^^^^^^^
required.

Looks OK to me. Thanks for catching this. I will test it out and if it
does not break any regression tests should go for the next rc.

Thanks!
>
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
> mm/frontswap.c | 2 +-
> mm/swapfile.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/frontswap.c b/mm/frontswap.c
> index 538367e..1b24bdc 100644
> --- a/mm/frontswap.c
> +++ b/mm/frontswap.c
> @@ -319,7 +319,7 @@ void __frontswap_invalidate_area(unsigned type)
> return;
> frontswap_ops->invalidate_area(type);
> atomic_set(&sis->frontswap_pages, 0);
> - memset(sis->frontswap_map, 0, sis->max / sizeof(long));
> + bitmap_zero(sis->frontswap_map, sis->max);
> }
> clear_bit(type, need_init);
> }
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 6c340d9..746af55b 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2116,7 +2116,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
> }
> /* frontswap enabled? set up bit-per-page map for frontswap */
> if (frontswap_enabled)
> - frontswap_map = vzalloc(maxpages / sizeof(long));
> + frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
>
> if (p->bdev) {
> if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
> --
> 1.8.1.4
>


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