linux-kernel - [PATCH v2 2/2] fs/ext4/xattr: Check for 'xattr_sem' inside 'ext4_xattr_delete

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Message-Id: <20250128082751.124948-3-bhupesh@igalia.com>
Date: Tue, 28 Jan 2025 13:57:51 +0530
From: Bhupesh <bhupesh@...lia.com>
To: linux-ext4@...r.kernel.org
Cc: bhupesh@...lia.com,
	tytso@....edu,
	kernel-dev@...lia.com,
	linux-kernel@...r.kernel.org,
	revest@...gle.com,
	adilger.kernel@...ger.ca,
	cascardo@...lia.com
Subject: [PATCH v2 2/2] fs/ext4/xattr: Check for 'xattr_sem' inside 'ext4_xattr_delete_inode'

Once we are inside the 'ext4_xattr_delete_inode' function and trying
to delete the inode, the 'xattr_sem' should be unlocked.

We need trylock here to avoid false-positive warning from lockdep
about reclaim circular dependency.

This makes the 'ext4_xattr_delete_inode' implementation mimic the
existing 'ext2_xattr_delete_inode' implementation and thus avoid
similar lockdep issues while deleting inodes.

Signed-off-by: Bhupesh <bhupesh@...lia.com>
---
 fs/ext4/xattr.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 6ff94cdf1515..b98267c09b00 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -2935,7 +2935,20 @@ int ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
 	struct ext4_iloc iloc = { .bh = NULL };
 	struct ext4_xattr_entry *entry;
 	struct inode *ea_inode;
-	int error;
+	int error = 0;
+
+	/*
+	 * We are the only ones holding inode reference. The xattr_sem should
+	 * better be unlocked! We could as well just not acquire xattr_sem at
+	 * all but this makes the code more futureproof. OTOH we need trylock
+	 * here to avoid false-positive warning from lockdep about reclaim
+	 * circular dependency.
+	 */
+	if (WARN_ON_ONCE(!down_write_trylock(&EXT4_I(inode)->xattr_sem)))
+		return error;
+
+	if (!EXT4_I(inode)->i_file_acl)
+		goto cleanup;
 
 	error = ext4_journal_ensure_credits(handle, extra_credits,
 			ext4_free_metadata_revoke_credits(inode->i_sb, 1));
@@ -3024,6 +3037,7 @@ int ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
 cleanup:
 	brelse(iloc.bh);
 	brelse(bh);
+	up_write(&EXT4_I(inode)->xattr_sem);
 	return error;
 }
 
-- 
2.38.1