linux-kernel - [RFC 2/2] writeback: Fix false warning in inode_to

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Message-ID: <20250407182104.716631-3-agruenba@redhat.com>
Date: Mon,  7 Apr 2025 20:21:02 +0200
From: Andreas Gruenbacher <agruenba@...hat.com>
To: cgroups@...r.kernel.org
Cc: Jan Kara <jack@...e.cz>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Rafael Aquini <aquini@...hat.com>,
	gfs2@...ts.linux.dev,
	linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Andreas Gruenbacher <agruenba@...hat.com>
Subject: [RFC 2/2] writeback: Fix false warning in inode_to_wb()

From: Jan Kara <jack@...e.cz>

inode_to_wb() is used also for filesystems that don't support cgroup
writeback. For these filesystems inode->i_wb is stable during the
lifetime of the inode (it points to bdi->wb) and there's no need to hold
locks protecting the inode->i_wb dereference. Improve the warning in
inode_to_wb() to not trigger for these filesystems.

Signed-off-by: Jan Kara <jack@...e.cz>
Reviewed-by: Andreas Gruenbacher <agruenba@...hat.com>
---
 include/linux/backing-dev.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 8e7af9a03b41..4069a027582f 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -245,10 +245,11 @@ wb_get_create_current(struct backing_dev_info *bdi, gfp_t gfp)
  * holding either @inode->i_lock, the i_pages lock, or the
  * associated wb's list_lock.
  */
-static inline struct bdi_writeback *inode_to_wb(const struct inode *inode)
+static inline struct bdi_writeback *inode_to_wb(struct inode *inode)
 {
 #ifdef CONFIG_LOCKDEP
 	WARN_ON_ONCE(debug_locks &&
+		     inode_cgwb_enabled(inode) &&
 		     (!lockdep_is_held(&inode->i_lock) &&
 		      !lockdep_is_held(&inode->i_mapping->i_pages.xa_lock) &&
 		      !lockdep_is_held(&inode->i_wb->list_lock)));
-- 
2.48.1