On 08/01/2016 05:59 PM, Alexander Potapenko wrote:
> If the total amount of memory assigned to quarantine is less than the
> amount of memory assigned to per-cpu quarantines, |new_quarantine_size|
> may overflow. Instead, set it to zero.
>
Just curious, how did find this?
Overflow is possible if system has more than 32 cpus per GB of memory. AFIAK this quite unusual.
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Fixes: 55834c59098d ("mm: kasan: initial memory quarantine
> implementation")
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
> mm/kasan/quarantine.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
> index 65793f1..416d3b0 100644
> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -196,7 +196,7 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
>
> void quarantine_reduce(void)
> {
> - size_t new_quarantine_size;
> + size_t new_quarantine_size, percpu_quarantines;
> unsigned long flags;
> struct qlist_head to_free = QLIST_INIT;
> size_t size_to_free = 0;
> @@ -214,7 +214,15 @@ void quarantine_reduce(void)
> */
> new_quarantine_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) /
> QUARANTINE_FRACTION;
> - new_quarantine_size -= QUARANTINE_PERCPU_SIZE * num_online_cpus();
> + percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
> + if (new_quarantine_size < percpu_quarantines) {
> + WARN_ONCE(1,
> + "Too little memory, disabling global KASAN quarantine.\n",
> + );
Why WARN? I'd suggest pr_warn_once();
> + new_quarantine_size = 0;
> + } else {
> + new_quarantine_size -= percpu_quarantines;
> + }
> WRITE_ONCE(quarantine_size, new_quarantine_size);
>
> last = global_quarantine.head;
>
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