[PATCH] z3fold: fix wrong handling of headless pages

[PATCH] z3fold: fix wrong handling of headless pages

[Jongseok Kim]

During the processing of headless pages in z3fold_reclaim_page(),
there was a problem that the zhdr pointed to another page
or a page was already released in z3fold_free(). So, the wrong page
is encoded in headless, or test_bit does not work properly
in z3fold_reclaim_page(). This patch fixed these problems.

Signed-off-by: Jongseok Kim <ks77sj@gmail.com>
---
 mm/z3fold.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 4b366d1..201a8ac 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -746,6 +746,9 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 	}
 
 	if (bud == HEADLESS) {
+		if (test_bit(UNDER_RECLAIM, &page->private))
+			return;
+
 		spin_lock(&pool->lock);
 		list_del(&page->lru);
 		spin_unlock(&pool->lock);
@@ -836,20 +839,20 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 		}
 		list_for_each_prev(pos, &pool->lru) {
 			page = list_entry(pos, struct page, lru);
+			zhdr = page_address(page);
 			if (test_bit(PAGE_HEADLESS, &page->private))
 				/* candidate found */
 				break;
 
-			zhdr = page_address(page);
 			if (!z3fold_page_trylock(zhdr))
 				continue; /* can't evict at this point */
 			kref_get(&zhdr->refcount);
 			list_del_init(&zhdr->buddy);
 			zhdr->cpu = -1;
-			set_bit(UNDER_RECLAIM, &page->private);
 			break;
 		}
 
+		set_bit(UNDER_RECLAIM, &page->private);
 		list_del_init(&page->lru);
 		spin_unlock(&pool->lock);
 
@@ -898,6 +901,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 		if (test_bit(PAGE_HEADLESS, &page->private)) {
 			if (ret == 0) {
 				free_z3fold_page(page);
+				atomic64_dec(&pool->pages_nr);
 				return 0;
 			}
 			spin_lock(&pool->lock);
-- 
2.7.4

Re: [PATCH] z3fold: fix wrong handling of headless pages

[Vitaly Wool]

Hi Jongseok,

Den fre 6 juli 2018 kl 07:11 skrev Jongseok Kim <ks77sj@gmail.com>:
>
> During the processing of headless pages in z3fold_reclaim_page(),
> there was a problem that the zhdr pointed to another page
> or a page was already released in z3fold_free(). So, the wrong page
> is encoded in headless, or test_bit does not work properly
> in z3fold_reclaim_page(). This patch fixed these problems.

thank you for your work, we've now got a more comprehensive solution:
https://lkml.org/lkml/2018/11/5/726

Would you please confirm that it works for you? Also, would you be
okay with dropping your patch in favor of the new one?

~Vitaly

> Signed-off-by: Jongseok Kim <ks77sj@gmail.com>
> ---
>  mm/z3fold.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 4b366d1..201a8ac 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -746,6 +746,9 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
>         }
>
>         if (bud == HEADLESS) {
> +               if (test_bit(UNDER_RECLAIM, &page->private))
> +                       return;
> +
>                 spin_lock(&pool->lock);
>                 list_del(&page->lru);
>                 spin_unlock(&pool->lock);
> @@ -836,20 +839,20 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>                 }
>                 list_for_each_prev(pos, &pool->lru) {
>                         page = list_entry(pos, struct page, lru);
> +                       zhdr = page_address(page);
>                         if (test_bit(PAGE_HEADLESS, &page->private))
>                                 /* candidate found */
>                                 break;
>
> -                       zhdr = page_address(page);
>                         if (!z3fold_page_trylock(zhdr))
>                                 continue; /* can't evict at this point */
>                         kref_get(&zhdr->refcount);
>                         list_del_init(&zhdr->buddy);
>                         zhdr->cpu = -1;
> -                       set_bit(UNDER_RECLAIM, &page->private);
>                         break;
>                 }
>
> +               set_bit(UNDER_RECLAIM, &page->private);
>                 list_del_init(&page->lru);
>                 spin_unlock(&pool->lock);
>
> @@ -898,6 +901,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>                 if (test_bit(PAGE_HEADLESS, &page->private)) {
>                         if (ret == 0) {
>                                 free_z3fold_page(page);
> +                               atomic64_dec(&pool->pages_nr);
>                                 return 0;
>                         }
>                         spin_lock(&pool->lock);
> --
> 2.7.4
>

Re: [PATCH] z3fold: fix wrong handling of headless pages

[Vitaly Wool]

Den tors 8 nov. 2018 kl 13:34 skrev 김종석 <ks77sj@gmail.com>:
>
> Hi Vitaly,
> thank you for the reply.
>
> I agree your a new solution is more comprehensive and drop my patch is simple way.
> But, I think it's not fair.
> If my previous patch was not wrong, is (my patch -> your patch) the right way?

I could apply the new patch on top of yours but that would effectively
revert most of your changes.
Would it be ok for you if I add you to Signed-off-by for the new patch instead?

~Vitaly

> I'm sorry I sent reply twice.
>
> Best regards,
> Jongseok
>
>
> > On 6/11/2018 4:48 PM, Vitaly Wool wrote:
> > Hi Jongseok,
>
> > thank you for your work, we've now got a more comprehensive solution:
> > https://lkml.org/lkml/2018/11/5/726
>
> > Would you please confirm that it works for you? Also, would you be
> >okay with dropping your patch in favor of the new one?
>
> > ~Vitaly

Re: [PATCH] z3fold: fix wrong handling of headless pages

[Jongseok Kim]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset=UTF-8, Size: 1035 bytes --]

Yes, you are right.
I think that's the best way to deal it.
Thank you.

Best regards,
Jongseok

> Den tors 8 nov. 2018 kl 13:34 skrev ±èÁ¾¼® <ks77sj@gmail.com>:
> >
> > Hi Vitaly,
> > thank you for the reply.
> >
> > I agree your a new solution is more comprehensive and drop my patch is simple way.
> > But, I think it's not fair.
> > If my previous patch was not wrong, is (my patch -> your patch) the right way?

> I could apply the new patch on top of yours but that would effectively
> revert most of your changes.
> Would it be ok for you if I add you to Signed-off-by for the new patch instead?

> ~Vitaly


> > I'm sorry I sent reply twice.
> >
> > Best regards,
> > Jongseok
> >
> >
> > > On 6/11/2018 4:48 PM, Vitaly Wool wrote:
> > > Hi Jongseok,
> >
> > > thank you for your work, we've now got a more comprehensive solution:
> > > https://lkml.org/lkml/2018/11/5/726
> >
> > > Would you please confirm that it works for you? Also, would you be
> > >okay with dropping your patch in favor of the new one?
> >
> > > ~Vitaly

Re: [PATCH] z3fold: fix wrong handling of headless pages

[Andrew Morton]

On Thu,  8 Nov 2018 22:45:40 +0900 Jongseok Kim <ks77sj@gmail.com> wrote:

> Yes, you are right.
> I think that's the best way to deal it.
> Thank you.


I did this:

Link: http://lkml.kernel.org/r/20181105162225.74e8837d03583a9b707cf559@gmail.com
Signed-off-by: Vitaly Wool <vitaly.vul@sony.com>
Signed-off-by: Jongseok Kim <ks77sj@gmail.com>
Reported-by-by: Jongseok Kim <ks77sj@gmail.com>
Reviewed-by: Snild Dolkow <snild@sony.com>