FAILED: patch "[PATCH] mm: zswap: fix missing folio cleanup in writeback race path" failed to apply to 6.7-stable tree

FAILED: patch "[PATCH] mm: zswap: fix missing folio cleanup in writeback race path" failed to apply to 6.7-stable tree

[gregkh]

The patch below does not apply to the 6.7-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.7.y
git checkout FETCH_HEAD
git cherry-pick -x e3b63e966cac0bf78aaa1efede1827a252815a1d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024022610-amino-basically-add3@gregkh' --subject-prefix 'PATCH 6.7.y' HEAD^..

Possible dependencies:

e3b63e966cac ("mm: zswap: fix missing folio cleanup in writeback race path")
96c7b0b42239 ("mm: return the folio from __read_swap_cache_async()")
e947ba0bbf47 ("mm/zswap: cleanup zswap_writeback_entry()")
32acba4c0483 ("mm/zswap: refactor out __zswap_load()")
c75f5c1e0f1d ("mm/zswap: reuse dstmem when decompress")
b5ba474f3f51 ("zswap: shrink zswap pool based on memory pressure")
a65b0e7607cc ("zswap: make shrinking memcg-aware")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e3b63e966cac0bf78aaa1efede1827a252815a1d Mon Sep 17 00:00:00 2001
From: Yosry Ahmed <yosryahmed@google.com>
Date: Thu, 25 Jan 2024 08:51:27 +0000
Subject: [PATCH] mm: zswap: fix missing folio cleanup in writeback race path

In zswap_writeback_entry(), after we get a folio from
__read_swap_cache_async(), we grab the tree lock again to check that the
swap entry was not invalidated and recycled.  If it was, we delete the
folio we just added to the swap cache and exit.

However, __read_swap_cache_async() returns the folio locked when it is
newly allocated, which is always true for this path, and the folio is
ref'd.  Make sure to unlock and put the folio before returning.

This was discovered by code inspection, probably because this path handles
a race condition that should not happen often, and the bug would not crash
the system, it will only strand the folio indefinitely.

Link: https://lkml.kernel.org/r/20240125085127.1327013-1-yosryahmed@google.com
Fixes: 04fc7816089c ("mm: fix zswap writeback race condition")
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/zswap.c b/mm/zswap.c
index 350dd2fc8159..d2423247acfd 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1440,6 +1440,8 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) {
 		spin_unlock(&tree->lock);
 		delete_from_swap_cache(folio);
+		folio_unlock(folio);
+		folio_put(folio);
 		return -ENOMEM;
 	}
 	spin_unlock(&tree->lock);

[PATCH 6.7.y] mm: zswap: fix missing folio cleanup in writeback race path

[Yosry Ahmed]

In zswap_writeback_entry(), after we get a folio from
__read_swap_cache_async(), we grab the tree lock again to check that the
swap entry was not invalidated and recycled.  If it was, we delete the
folio we just added to the swap cache and exit.

However, __read_swap_cache_async() returns the folio locked when it is
newly allocated, which is always true for this path, and the folio is
ref'd.  Make sure to unlock and put the folio before returning.

This was discovered by code inspection, probably because this path handles
a race condition that should not happen often, and the bug would not crash
the system, it will only strand the folio indefinitely.

Link: https://lkml.kernel.org/r/20240125085127.1327013-1-yosryahmed@google.com
Fixes: 04fc7816089c ("mm: fix zswap writeback race condition")
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit e3b63e966cac0bf78aaa1efede1827a252815a1d)
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
---
 mm/zswap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/zswap.c b/mm/zswap.c
index 74411dfdad925..b6f4a1a760578 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1105,6 +1105,8 @@ static int zswap_writeback_entry(struct zswap_entry *entry,
 	if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) {
 		spin_unlock(&tree->lock);
 		delete_from_swap_cache(page_folio(page));
+		unlock_page(page);
+		put_page(page);
 		ret = -ENOMEM;
 		goto fail;
 	}
-- 
2.44.0.rc1.240.g4c46232300-goog

Re: FAILED: patch "[PATCH] mm: zswap: fix missing folio cleanup in writeback race path" failed to apply to 6.7-stable tree

[Yosry Ahmed]

On Mon, Feb 26, 2024 at 11:30:10AM +0100, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.7-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.7.y
> git checkout FETCH_HEAD
> git cherry-pick -x e3b63e966cac0bf78aaa1efede1827a252815a1d
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024022610-amino-basically-add3@gregkh' --subject-prefix 'PATCH 6.7.y' HEAD^..

First time sending backports to stable. I think I slightly butchered the
6.1 and 6.6 patches. The first one has an extra `Change-Id` footer and
no additional `Signed-off-by` (although my original one exists), while
the latter has no 6.6.y prefix. I think I got 6.7 right tho :)

Greg, please let me know if I need to resend the backports for 6.1
and/or 6.6, and sorry for any inconvenience.

Re: FAILED: patch "[PATCH] mm: zswap: fix missing folio cleanup in writeback race path" failed to apply to 6.7-stable tree

[Greg KH]

On Mon, Feb 26, 2024 at 10:20:45PM +0000, Yosry Ahmed wrote:
> On Mon, Feb 26, 2024 at 11:30:10AM +0100, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 6.7-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> > 
> > To reproduce the conflict and resubmit, you may use the following commands:
> > 
> > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.7.y
> > git checkout FETCH_HEAD
> > git cherry-pick -x e3b63e966cac0bf78aaa1efede1827a252815a1d
> > # <resolve conflicts, build, test, etc.>
> > git commit -s
> > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024022610-amino-basically-add3@gregkh' --subject-prefix 'PATCH 6.7.y' HEAD^..
> 
> First time sending backports to stable. I think I slightly butchered the
> 6.1 and 6.6 patches. The first one has an extra `Change-Id` footer and
> no additional `Signed-off-by` (although my original one exists), while
> the latter has no 6.6.y prefix. I think I got 6.7 right tho :)
> 
> Greg, please let me know if I need to resend the backports for 6.1
> and/or 6.6, and sorry for any inconvenience.

Yes, please do, I have no idea what branches any of these are for :(

Please give me a hint somehow...

thanks,

greg k-h

Re: [PATCH 6.7.y] mm: zswap: fix missing folio cleanup in writeback race path

[Greg KH]

On Mon, Feb 26, 2024 at 10:16:47PM +0000, Yosry Ahmed wrote:
> In zswap_writeback_entry(), after we get a folio from
> __read_swap_cache_async(), we grab the tree lock again to check that the
> swap entry was not invalidated and recycled.  If it was, we delete the
> folio we just added to the swap cache and exit.
> 
> However, __read_swap_cache_async() returns the folio locked when it is
> newly allocated, which is always true for this path, and the folio is
> ref'd.  Make sure to unlock and put the folio before returning.
> 
> This was discovered by code inspection, probably because this path handles
> a race condition that should not happen often, and the bug would not crash
> the system, it will only strand the folio indefinitely.
> 
> Link: https://lkml.kernel.org/r/20240125085127.1327013-1-yosryahmed@google.com
> Fixes: 04fc7816089c ("mm: fix zswap writeback race condition")
> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
> Reviewed-by: Chengming Zhou <zhouchengming@bytedance.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Reviewed-by: Nhat Pham <nphamcs@gmail.com>
> Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> (cherry picked from commit e3b63e966cac0bf78aaa1efede1827a252815a1d)
> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
> ---
>  mm/zswap.c | 2 ++
>  1 file changed, 2 insertions(+)

Now queued up, thanks.

greg k-h