FAILED: patch "[PATCH] btrfs: fix folio leak in submit_one_async_extent()" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x a0fd1c6098633f9a95fc2f636383546c82b704c3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025051949-line-blog-2ffe@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From a0fd1c6098633f9a95fc2f636383546c82b704c3 Mon Sep 17 00:00:00 2001
From: Boris Burkov <[email protected]>
Date: Wed, 7 May 2025 12:42:24 -0700
Subject: [PATCH] btrfs: fix folio leak in submit_one_async_extent()

If btrfs_reserve_extent() fails while submitting an async_extent for a compressed write, then we fail to call free_async_extent_pages() on the async_extent and leak its folios. A likely cause for such a failure would be btrfs_reserve_extent() failing to find a large enough contiguous free extent for the compressed extent.

I was able to reproduce this by:

1. mount with compress-force=zstd:3
2. fallocating most of a filesystem to a big file
3. fragmenting the remaining free space
4. trying to copy in a file which zstd would generate large compressed extents for (vmlinux worked well for this)

Step 4. hits the memory leak and can be repeated ad nauseam to eventually exhaust the system memory.

Fix this by detecting the case where we fallback to uncompressed submission for a compressed async_extent and ensuring that we call free_async_extent_pages().

index d295a37fa049..c1bd17915f81 100644
@@ -1109,6 +1109,7 @@ static void submit_one_async_extent(struct async_chunk *async_chunk,
 	struct extent_state *cached = NULL;
 	struct extent_map *em;
 	int ret = 0;
+	bool free_pages = false;
 	u64 start = async_extent->start;
 	u64 end = async_extent->start + async_extent->ram_size - 1;
 

@@ -1129,7 +1130,10 @@ static void submit_one_async_extent(struct async_chunk *async_chunk,
 	}
 
 	if (async_extent->compress_type == BTRFS_COMPRESS_NONE) {
+		ASSERT(!async_extent->folios);
+		ASSERT(async_extent->nr_folios == 0);
 		submit_uncompressed_range(inode, async_extent, locked_folio);
+		free_pages = true;
 		goto done;
 	}
 

@@ -1145,6 +1149,7 @@ static void submit_one_async_extent(struct async_chunk *async_chunk,
 		 * fall back to uncompressed.
 		 */
 		submit_uncompressed_range(inode, async_extent, locked_folio);
+		free_pages = true;
 		goto done;
 	}
 

@@ -1186,6 +1191,8 @@ static void submit_one_async_extent(struct async_chunk *async_chunk,
 done:
 	if (async_chunk->blkcg_css)
 		kthread_associate_blkcg(NULL);
+	if (free_pages)
+		free_async_extent_pages(async_extent);
 	kfree(async_extent);
 	return;