FAILED: patch "[PATCH] btrfs: fix encoded write i_size corruption with no-holes" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x e7db9e5c6b9615b287d01f0231904fbc1fbde9c5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023051355-such-snowfall-6415@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

e7db9e5c6b96 ("btrfs: fix encoded write i_size corruption with no-holes") 76aea5379678 ("btrfs: make btrfs_inode_safe_disk_i_size_write take btrfs_inode") 2766ff61762c ("btrfs: update the number of bytes used by an inode atomically") 5893dfb98f25 ("btrfs: refactor btrfs_drop_extents() to make it easier to extend") ac5887c8e013 ("btrfs: locking: remove all the blocking helpers") a14b78ad06ab ("btrfs: introduce btrfs_inode_lock()/unlock()")
b8d8e1fd570a ("btrfs: introduce btrfs_write_check()")
c86537a42f86 ("btrfs: check FS error state bit early during write") 5e8b9ef30392 ("btrfs: move pos increment and pagecache extension to btrfs_buffered_write") 4e4cabece9f9 ("btrfs: split btrfs_direct_IO to read and write") 196d59ab9ccc ("btrfs: switch extent buffer tree lock to rw_semaphore")

thanks,

greg k-h

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

From e7db9e5c6b9615b287d01f0231904fbc1fbde9c5 Mon Sep 17 00:00:00 2001
From: Boris Burkov <[email protected]>
Date: Fri, 28 Apr 2023 14:02:11 -0700
Subject: [PATCH] btrfs: fix encoded write i_size corruption with no-holes

We have observed a btrfs filesystem corruption on workloads using no-holes and encoded writes via send stream v2. The symptom is that a file appears to be truncated to the end of its last aligned extent, even though the final unaligned extent and even the file extent and otherwise correctly updated inode item have been written.

So if we were writing out a 1MiB+X file via 8 128K extents and one extent of length X, i_size would be set to 1MiB, but the ninth extent, nbyte, etc. would all appear correct otherwise.

The source of the race is a narrow (one line of code) window in which a no-holes fs has read in an updated i_size, but has not yet set a shared disk_i_size variable to write. Therefore, if two ordered extents run in parallel (par for the course for receive workloads), the following sequence can play out: (following "threads" a bit loosely, since there are callbacks involved for endio but extra threads aren't needed to cause the issue)

ENC-WR1 (second to last) ENC-WR2 (last)
------- -------
btrfs_do_encoded_write
set i_size = 1M
submit bio B1 ending at 1M
endio B1
btrfs_inode_safe_disk_i_size_write
local i_size = 1M
falls off a cliff for some reason
btrfs_do_encoded_write
set i_size = 1M+X submit bio B2 ending at 1M+X
endio B2 btrfs_inode_safe_disk_i_size_write
local i_size = 1M+X disk_i_size = 1M+X
disk_i_size = 1M
btrfs_delayed_update_inode
btrfs_delayed_update_inode

And the delayed inode ends up filled with nbytes=1M+X and isize=1M, and writes respect i_size and present a corrupted file missing its last extents.

Fix this by holding the inode lock in the no-holes case so that a thread can't sneak in a write to disk_i_size that gets overwritten with an out of date i_size.

index 018c711a0bc8..cd4cce9ba443 100644
@@ -52,13 +52,13 @@ void btrfs_inode_safe_disk_i_size_write(struct btrfs_inode *inode, u64 new_i_siz
 	u64 start, end, i_size;
 	int ret;
 
+	spin_lock(&inode->lock);
 	i_size = new_i_size ?: i_size_read(&inode->vfs_inode);
 	if (btrfs_fs_incompat(fs_info, NO_HOLES)) {
 		inode->disk_i_size = i_size;
-		return;
+		goto out_unlock;
 	}
 
-	spin_lock(&inode->lock);
 	ret = find_contiguous_extent_bit(&inode->file_extent_tree, 0, &start,
 					 &end, EXTENT_DIRTY);
 	if (!ret && start == 0)

@@ -66,6 +66,7 @@ void btrfs_inode_safe_disk_i_size_write(struct btrfs_inode *inode, u64 new_i_siz
 	else
 		i_size = 0;
 	inode->disk_i_size = i_size;
+out_unlock:
 	spin_unlock(&inode->lock);
 }