Re: [PATCH] xen: fix broken tainted value in mark_page_free

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Penny,

> On 22 Sep 2021, at 12:44, Penny Zheng <penny.zheng@xxxxxxx> wrote:
> 
> Commit 540a637c3410780b519fc055f432afe271f642f8 defines a new
> helper mark_page_free to extract common codes, while it accidently
> breaks the local variable "tainted".
> 
> This patch fix it by letting mark_page_free() return bool of whether the
> page is offlined and rename local variable "tainted" to "pg_offlined".
> 
> Coverity ID: 1491872
> 
> Fixes: 540a637c3410780b519fc055f432afe271f642f8
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Cheers
Bertrand

> ---
> v2 changes:
> - rename local variable "tainted" to "pg_offlined", and make it bool
> ---
> xen/common/page_alloc.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
> index 6142c7bb6a..5801358b4b 100644
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1380,8 +1380,10 @@ bool scrub_free_pages(void)
>     return node_to_scrub(false) != NUMA_NO_NODE;
> }
> 
> -static void mark_page_free(struct page_info *pg, mfn_t mfn)
> +static bool mark_page_free(struct page_info *pg, mfn_t mfn)
> {
> +    bool pg_offlined = false;
> +
>     ASSERT(mfn_x(mfn) == mfn_x(page_to_mfn(pg)));
> 
>     /*
> @@ -1405,7 +1407,7 @@ static void mark_page_free(struct page_info *pg, mfn_t 
> mfn)
>     case PGC_state_offlining:
>         pg->count_info = (pg->count_info & PGC_broken) |
>                          PGC_state_offlined;
> -        tainted = 1;
> +        pg_offlined = true;
>         break;
> 
>     default:
> @@ -1425,6 +1427,8 @@ static void mark_page_free(struct page_info *pg, mfn_t 
> mfn)
>     /* This page is not a guest frame any more. */
>     page_set_owner(pg, NULL); /* set_gpfn_from_mfn snoops pg owner */
>     set_gpfn_from_mfn(mfn_x(mfn), INVALID_M2P_ENTRY);
> +
> +    return pg_offlined;
> }
> 
> /* Free 2^@order set of pages. */
> @@ -1433,7 +1437,7 @@ static void free_heap_pages(
> {
>     unsigned long mask;
>     mfn_t mfn = page_to_mfn(pg);
> -    unsigned int i, node = phys_to_nid(mfn_to_maddr(mfn)), tainted = 0;
> +    unsigned int i, node = phys_to_nid(mfn_to_maddr(mfn)), pg_offlined = 0;
>     unsigned int zone = page_to_zone(pg);
> 
>     ASSERT(order <= MAX_ORDER);
> @@ -1443,7 +1447,8 @@ static void free_heap_pages(
> 
>     for ( i = 0; i < (1 << order); i++ )
>     {
> -        mark_page_free(&pg[i], mfn_add(mfn, i));
> +        if ( mark_page_free(&pg[i], mfn_add(mfn, i)) )
> +            pg_offlined = 1;
> 
>         if ( need_scrub )
>         {
> @@ -1517,7 +1522,7 @@ static void free_heap_pages(
> 
>     page_list_add_scrub(pg, node, zone, order, pg->u.free.first_dirty);
> 
> -    if ( tainted )
> +    if ( pg_offlined )
>         reserve_offlined_page(pg);
> 
>     spin_unlock(&heap_lock);
> -- 
> 2.25.1
>