[PATCH] mm: frontswap: invalidate expired data on a dup-store failure

[PATCH] mm: frontswap: invalidate expired data on a dup-store failure

[Weijie Yang]

If a frontswap dup-store failed, it should invalidate the expired page
in the backend, or it could trigger some data corruption issue.
Such as:
1. use zswap as the frontswap backend with writeback feature
2. store a swap page(version_1) to entry A, success
3. dup-store a newer page(version_2) to the same entry A, fail
4. use __swap_writepage() write version_2 page to swapfile, success
5. zswap do shrink, writeback version_1 page to swapfile
6. version_2 page is overwrited by version_1, data corrupt.

This patch fixes this issue by invalidating expired data immediately
when meet a dup-store failure.

Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
---
 mm/frontswap.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/mm/frontswap.c b/mm/frontswap.c
index c30eec5..f2a3571 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
 		  the (older) page from frontswap
 		 */
 		inc_frontswap_failed_stores();
-		if (dup)
+		if (dup) {
 			__frontswap_clear(sis, offset);
+			frontswap_ops->invalidate_page(type, offset);
+		}
 	}
 	if (frontswap_writethrough_enabled)
 		/* report failure so swap also writes to swap device */
-- 
1.7.0.4

Re: [PATCH] mm: frontswap: invalidate expired data on a dup-store failure

[Andrew Morton]

On Tue, 18 Nov 2014 16:51:36 +0800 Weijie Yang <weijie.yang@samsung.com> wrote:

> If a frontswap dup-store failed, it should invalidate the expired page
> in the backend, or it could trigger some data corruption issue.
> Such as:
> 1. use zswap as the frontswap backend with writeback feature
> 2. store a swap page(version_1) to entry A, success
> 3. dup-store a newer page(version_2) to the same entry A, fail
> 4. use __swap_writepage() write version_2 page to swapfile, success
> 5. zswap do shrink, writeback version_1 page to swapfile
> 6. version_2 page is overwrited by version_1, data corrupt.
> 
> This patch fixes this issue by invalidating expired data immediately
> when meet a dup-store failure.
> 
> ...
>
> --- a/mm/frontswap.c
> +++ b/mm/frontswap.c
> @@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
>  		  the (older) page from frontswap
>  		 */
>  		inc_frontswap_failed_stores();
> -		if (dup)
> +		if (dup) {
>  			__frontswap_clear(sis, offset);
> +			frontswap_ops->invalidate_page(type, offset);
> +		}
>  	}
>  	if (frontswap_writethrough_enabled)
>  		/* report failure so swap also writes to swap device */

I tagged this for backporting into -stable kernels.  Please shout at me
if you think that was inappropriate.

Re: [PATCH] mm: frontswap: invalidate expired data on a dup-store failure

[Seth Jennings]

On Tue, Nov 18, 2014 at 04:51:36PM +0800, Weijie Yang wrote:
> If a frontswap dup-store failed, it should invalidate the expired page
> in the backend, or it could trigger some data corruption issue.
> Such as:
> 1. use zswap as the frontswap backend with writeback feature
> 2. store a swap page(version_1) to entry A, success
> 3. dup-store a newer page(version_2) to the same entry A, fail
> 4. use __swap_writepage() write version_2 page to swapfile, success
> 5. zswap do shrink, writeback version_1 page to swapfile
> 6. version_2 page is overwrited by version_1, data corrupt.

Good catch!

> 
> This patch fixes this issue by invalidating expired data immediately
> when meet a dup-store failure.
> 
> Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
> ---
>  mm/frontswap.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/frontswap.c b/mm/frontswap.c
> index c30eec5..f2a3571 100644
> --- a/mm/frontswap.c
> +++ b/mm/frontswap.c
> @@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
>  		  the (older) page from frontswap
>  		 */
>  		inc_frontswap_failed_stores();
> -		if (dup)
> +		if (dup) {
>  			__frontswap_clear(sis, offset);
> +			frontswap_ops->invalidate_page(type, offset);

Looking at __frontswap_invalidate_page(), should we do
inc_frontswap_invalidates() too?  If so, maybe we should just call
__frontswap_invalidate_page().

Thanks,
Seth

> +		}
>  	}
>  	if (frontswap_writethrough_enabled)
>  		/* report failure so swap also writes to swap device */
> -- 
> 1.7.0.4
> 
> 
> --
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Re: [PATCH] mm: frontswap: invalidate expired data on a dup-store failure

[Weijie Yang]

On Wed, Nov 19, 2014 at 6:29 AM, Seth Jennings <sjennings@variantweb.net> wrote:
> On Tue, Nov 18, 2014 at 04:51:36PM +0800, Weijie Yang wrote:
>> If a frontswap dup-store failed, it should invalidate the expired page
>> in the backend, or it could trigger some data corruption issue.
>> Such as:
>> 1. use zswap as the frontswap backend with writeback feature
>> 2. store a swap page(version_1) to entry A, success
>> 3. dup-store a newer page(version_2) to the same entry A, fail
>> 4. use __swap_writepage() write version_2 page to swapfile, success
>> 5. zswap do shrink, writeback version_1 page to swapfile
>> 6. version_2 page is overwrited by version_1, data corrupt.
>
> Good catch!
>
>>
>> This patch fixes this issue by invalidating expired data immediately
>> when meet a dup-store failure.
>>
>> Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
>> ---
>>  mm/frontswap.c |    4 +++-
>>  1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/frontswap.c b/mm/frontswap.c
>> index c30eec5..f2a3571 100644
>> --- a/mm/frontswap.c
>> +++ b/mm/frontswap.c
>> @@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
>>                 the (older) page from frontswap
>>                */
>>               inc_frontswap_failed_stores();
>> -             if (dup)
>> +             if (dup) {
>>                       __frontswap_clear(sis, offset);
>> +                     frontswap_ops->invalidate_page(type, offset);
>
> Looking at __frontswap_invalidate_page(), should we do
> inc_frontswap_invalidates() too?  If so, maybe we should just call
> __frontswap_invalidate_page().

The frontswap_invalidate_page() is for swap_entry_free, while here
is an inner ops for dup-store, so I think there is no need for
inc_frontswap_invalidates().

> Thanks,
> Seth
>
>> +             }
>>       }
>>       if (frontswap_writethrough_enabled)
>>               /* report failure so swap also writes to swap device */
>> --
>> 1.7.0.4
>>
>>
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@kvack.org.  For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

Re: [PATCH] mm: frontswap: invalidate expired data on a dup-store failure

[Seth Jennings]

On Wed, Nov 19, 2014 at 09:06:41PM +0800, Weijie Yang wrote:
> On Wed, Nov 19, 2014 at 6:29 AM, Seth Jennings <sjennings@variantweb.net> wrote:
> > On Tue, Nov 18, 2014 at 04:51:36PM +0800, Weijie Yang wrote:
> >> If a frontswap dup-store failed, it should invalidate the expired page
> >> in the backend, or it could trigger some data corruption issue.
> >> Such as:
> >> 1. use zswap as the frontswap backend with writeback feature
> >> 2. store a swap page(version_1) to entry A, success
> >> 3. dup-store a newer page(version_2) to the same entry A, fail
> >> 4. use __swap_writepage() write version_2 page to swapfile, success
> >> 5. zswap do shrink, writeback version_1 page to swapfile
> >> 6. version_2 page is overwrited by version_1, data corrupt.
> >
> > Good catch!
> >
> >>
> >> This patch fixes this issue by invalidating expired data immediately
> >> when meet a dup-store failure.
> >>
> >> Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
> >> ---
> >>  mm/frontswap.c |    4 +++-
> >>  1 files changed, 3 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/mm/frontswap.c b/mm/frontswap.c
> >> index c30eec5..f2a3571 100644
> >> --- a/mm/frontswap.c
> >> +++ b/mm/frontswap.c
> >> @@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
> >>                 the (older) page from frontswap
> >>                */
> >>               inc_frontswap_failed_stores();
> >> -             if (dup)
> >> +             if (dup) {
> >>                       __frontswap_clear(sis, offset);
> >> +                     frontswap_ops->invalidate_page(type, offset);
> >
> > Looking at __frontswap_invalidate_page(), should we do
> > inc_frontswap_invalidates() too?  If so, maybe we should just call
> > __frontswap_invalidate_page().
> 
> The frontswap_invalidate_page() is for swap_entry_free, while here
> is an inner ops for dup-store, so I think there is no need for
> inc_frontswap_invalidates().

In my mind, I agree we shouldn't call __frontswap_invalidate_page(),
just to keep things separated.

Andrew has already pulled it in and it isn't a big deal.  Just a
statistics thing on a rare situation (dup) counted along with lots
of frequent situations (normal invalidate).  Which makes me think
we make want to count dup-invalidates as a separate stat.  But that
would be a separate patch too :)

Thanks,
Seth

> 
> > Thanks,
> > Seth
> >
> >> +             }
> >>       }
> >>       if (frontswap_writethrough_enabled)
> >>               /* report failure so swap also writes to swap device */
> >> --
> >> 1.7.0.4
> >>
> >>
> >> --
> >> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> >> the body to majordomo@kvack.org.  For more info on Linux MM,
> >> see: http://www.linux-mm.org/ .
> >> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>