[PATCH] mm: memory-failure: fix potential page refcnt leak in memory_failure()

[PATCH] mm: memory-failure: fix potential page refcnt leak in memory_failure()

[Miaohe Lin]

put_ref_page() is not called to drop extra refcnt when comes from madvise
in the case pfn is valid but pgmap is NULL leading to page refcnt leak.

Fixes: 1e8aaedb182d ("mm,memory_failure: always pin the page in madvise_inject_error")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/memory-failure.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index e245191e6b04..65e2d4c5b50d 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2080,8 +2080,6 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
 {
 	int rc = -ENXIO;
 
-	put_ref_page(pfn, flags);
-
 	/* device metadata space is not recoverable */
 	if (!pgmap_pfn_valid(pgmap, pfn))
 		goto out;
@@ -2157,6 +2155,7 @@ int memory_failure(unsigned long pfn, int flags)
 
 		if (pfn_valid(pfn)) {
 			pgmap = get_dev_pagemap(pfn, NULL);
+			put_ref_page(pfn, flags);
 			if (pgmap) {
 				res = memory_failure_dev_pagemap(pfn, flags,
 								 pgmap);
-- 
2.33.0

Re: [PATCH] mm: memory-failure: fix potential page refcnt leak in memory_failure()

[Naoya Horiguchi]

On Sat, Jul 01, 2023 at 03:28:37PM +0800, Miaohe Lin wrote:
> put_ref_page() is not called to drop extra refcnt when comes from madvise
> in the case pfn is valid but pgmap is NULL leading to page refcnt leak.

Is this test scenario realistic one?  I don't think that we can call madvise() for
such a device memory page.  If this is the case, this issue can be thought as
potentioal one (so no need to send to stable). 

> 
> Fixes: 1e8aaedb182d ("mm,memory_failure: always pin the page in madvise_inject_error")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Anyway, the patch looks good to me. Thanks you.

Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>

> ---
>  mm/memory-failure.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index e245191e6b04..65e2d4c5b50d 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2080,8 +2080,6 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
>  {
>  	int rc = -ENXIO;
>  
> -	put_ref_page(pfn, flags);
> -
>  	/* device metadata space is not recoverable */
>  	if (!pgmap_pfn_valid(pgmap, pfn))
>  		goto out;
> @@ -2157,6 +2155,7 @@ int memory_failure(unsigned long pfn, int flags)
>  
>  		if (pfn_valid(pfn)) {
>  			pgmap = get_dev_pagemap(pfn, NULL);
> +			put_ref_page(pfn, flags);
>  			if (pgmap) {
>  				res = memory_failure_dev_pagemap(pfn, flags,
>  								 pgmap);
> -- 
> 2.33.0
> 
> 
> 

Re: [PATCH] mm: memory-failure: fix potential page refcnt leak in memory_failure()

[Miaohe Lin]

On 2023/7/3 14:37, Naoya Horiguchi wrote:
> On Sat, Jul 01, 2023 at 03:28:37PM +0800, Miaohe Lin wrote:
>> put_ref_page() is not called to drop extra refcnt when comes from madvise
>> in the case pfn is valid but pgmap is NULL leading to page refcnt leak.
> 
> Is this test scenario realistic one?  I don't think that we can call madvise() for
> such a device memory page.  If this is the case, this issue can be thought as
> potentioal one (so no need to send to stable). 

This is a theoretical problem. If pagemap can ever be NULL after page refcnt is increased, this
would occur. I think it's not needed to send to stable too.

> 
>>
>> Fixes: 1e8aaedb182d ("mm,memory_failure: always pin the page in madvise_inject_error")
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> 
> Anyway, the patch looks good to me. Thanks you.
> 
> Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>

Thanks for your review and comment.