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

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 <[email protected]>.

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 '<[email protected]>' --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 <[email protected]>
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.

index 350dd2fc8159..d2423247acfd 100644
@@ -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);

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.

---
 mm/zswap.c | 2 ++
 1 file changed, 2 insertions(+)

index 74411dfdad925..b6f4a1a760578 100644
@@ -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

Now queued up, thanks.

greg k-h

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