linux-ext4 - [PATCH] ext4: Don't run ext4lazyinit for read-only filesystems

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Date:   Sun, 31 Jul 2022 20:24:53 -0700
From:   Josh Triplett <josh@...htriplett.org>
To:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>
Cc:     linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] ext4: Don't run ext4lazyinit for read-only filesystems

On a read-only filesystem, we won't invoke the block allocator, so we
don't need to prefetch the block bitmaps.

This avoids starting and running the ext4lazyinit thread at all on a
system with no read-write ext4 filesystems (for instance, a container VM
with read-only filesystems underneath an overlayfs).

Fixes: 21175ca434c5 ("ext4: make prefetch_block_bitmaps default")
Signed-off-by: Josh Triplett <josh@...htriplett.org>
---

Tested in a VM, with a read-only ext4 root filesystem. Confirmed that
ext4lazyinit starts without this patch, and does not start with this
patch.

(For a future merge window, not the current one. Please let me know if I
need to re-send this at a later, more convenient time.)

 fs/ext4/super.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 845f2f8aee5f..20437acc8865 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3973,9 +3973,9 @@ int ext4_register_li_request(struct super_block *sb,
 		goto out;
 	}

-	if (test_opt(sb, NO_PREFETCH_BLOCK_BITMAPS) &&
-	    (first_not_zeroed == ngroups || sb_rdonly(sb) ||
-	     !test_opt(sb, INIT_INODE_TABLE)))
+	if (sb_rdonly(sb) ||
+	    (test_opt(sb, NO_PREFETCH_BLOCK_BITMAPS) &&
+	     (first_not_zeroed == ngroups || !test_opt(sb, INIT_INODE_TABLE))))
 		goto out;

 	elr = ext4_li_request_new(sb, first_not_zeroed);
-- 
2.36.1