linux-kernel - [PATCH] ext4: clear DISCARD flag if device does not support discard

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Message-Id: <20250311021310.669524-1-lidiangang@bytedance.com>
Date: Tue, 11 Mar 2025 10:13:10 +0800
From: Diangang Li <lidiangang@...edance.com>
To: tytso@....edu,
	adilger.kernel@...ger.ca
Cc: linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Diangang Li <lidiangang@...edance.com>
Subject: [PATCH] ext4: clear DISCARD flag if device does not support discard

commit 79add3a3f795e ("ext4: notify when discard is not supported")
noted that keeping the DISCARD flag is for possibility that the underlying
device might change in future even without file system remount. However,
this scenario has rarely occurred in practice on the device side. Even if
it does occur, it can be resolved with remount. Clearing the DISCARD flag
not only prevents confusion caused by mount options but also avoids
sending unnecessary discard commands.

Signed-off-by: Diangang Li <lidiangang@...edance.com>
---
 fs/ext4/super.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a50e5c31b937..1b4d8475a08c 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5616,9 +5616,11 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 			goto failed_mount9;
 	}
 
-	if (test_opt(sb, DISCARD) && !bdev_max_discard_sectors(sb->s_bdev))
+	if (test_opt(sb, DISCARD) && !bdev_max_discard_sectors(sb->s_bdev)) {
 		ext4_msg(sb, KERN_WARNING,
 			 "mounting with \"discard\" option, but the device does not support discard");
+		clear_opt(sb, DISCARD);
+	}
 
 	if (es->s_error_count)
 		mod_timer(&sbi->s_err_report, jiffies + 300*HZ); /* 5 minutes */
-- 
2.20.1