linux-kernel - [PATCH v8 1/8] writeback, cgroup: do not switch inodes with I_WILL

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Date:   Mon, 7 Jun 2021 18:31:16 -0700
From:   Roman Gushchin <guro@...com>
To:     Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>
CC:     <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, Alexander Viro <viro@...iv.linux.org.uk>,
        Dennis Zhou <dennis@...nel.org>,
        Dave Chinner <dchinner@...hat.com>, <cgroups@...r.kernel.org>,
        Roman Gushchin <guro@...com>
Subject: [PATCH v8 1/8] writeback, cgroup: do not switch inodes with I_WILL_FREE flag

If an inode's state has I_WILL_FREE flag set, the inode will be
freed soon, so there is no point in trying to switch the inode
to a different cgwb.

I_WILL_FREE was ignored since the introduction of the inode switching,
so it looks like it doesn't lead to any noticeable issues for a user.
This is why the patch is not intended for a stable backport.

Suggested-by: Jan Kara <jack@...e.cz>
Signed-off-by: Roman Gushchin <guro@...com>
Acked-by: Tejun Heo <tj@...nel.org>
Reviewed-by: Jan Kara <jack@...e.cz>
Acked-by: Dennis Zhou <dennis@...nel.org>
---
 fs/fs-writeback.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e91980f49388..bd99890599e0 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -389,10 +389,10 @@ static void inode_switch_wbs_work_fn(struct work_struct *work)
 	xa_lock_irq(&mapping->i_pages);
 
 	/*
-	 * Once I_FREEING is visible under i_lock, the eviction path owns
-	 * the inode and we shouldn't modify ->i_io_list.
+	 * Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
+	 * path owns the inode and we shouldn't modify ->i_io_list.
 	 */
-	if (unlikely(inode->i_state & I_FREEING))
+	if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
 		goto skip_switch;
 
 	trace_inode_switch_wbs(inode, old_wb, new_wb);
@@ -517,7 +517,7 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id)
 	/* while holding I_WB_SWITCH, no one else can update the association */
 	spin_lock(&inode->i_lock);
 	if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
-	    inode->i_state & (I_WB_SWITCH | I_FREEING) ||
+	    inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
 	    inode_to_wb(inode) == isw->new_wb) {
 		spin_unlock(&inode->i_lock);
 		goto out_free;
-- 
2.31.1