linux-ext4 - [PATCH 2/2] fs: record I_DIRTY_TIME even if inode already has I_DIRTY

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Date:   Thu, 28 Jul 2022 15:39:14 +0200
From:   Lukas Czerner <lczerner@...hat.com>
To:     linux-ext4@...r.kernel.org
Cc:     jlayton@...nel.org, tytso@....edu, linux-fsdevel@...r.kernel.org
Subject: [PATCH 2/2] fs: record I_DIRTY_TIME even if inode already has I_DIRTY_INODE

Currently the I_DIRTY_TIME will never get set if the inode already has
I_DIRTY_INODE with assumption that it supersedes I_DIRTY_TIME.  That's
true, however ext4 will only update the on-disk inode in
->dirty_inode(), not on actual writeback. As a result if the inode
already has I_DIRTY_INODE state by the time we get to
__mark_inode_dirty() only with I_DIRTY_TIME, the time was already filled
into on-disk inode and will not get updated until the next I_DIRTY_INODE
update, which might never come if we crash or get a power failure.

The problem can be reproduced on ext4 by running xfstest generic/622
with -o iversion mount option. Fix it by setting I_DIRTY_TIME even if
the inode already has I_DIRTY_INODE.

Also clear the I_DIRTY_TIME after ->dirty_inode() otherwise it may never
get cleared.

Signed-off-by: Lukas Czerner <lczerner@...hat.com>
---
 fs/fs-writeback.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 05221366a16d..174f01e6b912 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -2383,6 +2383,11 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 
 		/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
 		flags &= ~I_DIRTY_TIME;
+		if (inode->i_state & I_DIRTY_TIME) {
+			spin_lock(&inode->i_lock);
+			inode->i_state &= ~I_DIRTY_TIME;
+			spin_unlock(&inode->i_lock);
+		}
 	} else {
 		/*
 		 * Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
@@ -2399,13 +2404,20 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 	 */
 	smp_mb();
 
-	if (((inode->i_state & flags) == flags) ||
-	    (dirtytime && (inode->i_state & I_DIRTY_INODE)))
+	if ((inode->i_state & flags) == flags)
 		return;
 
 	spin_lock(&inode->i_lock);
-	if (dirtytime && (inode->i_state & I_DIRTY_INODE))
+	if (dirtytime && (inode->i_state & I_DIRTY_INODE)) {
+		/*
+		 * We've got a new lazytime update. Make sure it's recorded in
+		 * i_state, because the time might have already got updated in
+		 * ->dirty_inode() and will not get updated until next
+		 *  I_DIRTY_INODE update.
+		 */
+		inode->i_state |= I_DIRTY_TIME;
 		goto out_unlock_inode;
+	}
 	if ((inode->i_state & flags) != flags) {
 		const int was_dirty = inode->i_state & I_DIRTY;
 
-- 
2.35.3