linux-kernel - [PATCH] erofs: correct FSDAX detection

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Message-ID: <20251117115729.626525-1-hsiangkao@linux.alibaba.com>
Date: Mon, 17 Nov 2025 19:57:29 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: linux-erofs@...ts.ozlabs.org
Cc: LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Gao Xiang <hsiangkao@...ux.alibaba.com>,
	syzbot+31b8fb02cb8a25bd5e78@...kaller.appspotmail.com,
	Yuezhang Mo <Yuezhang.Mo@...y.com>
Subject: [PATCH] erofs: correct FSDAX detection

The detection of the primary device is skipped incorrectly
if the multiple or flattened feature is enabled.

It also fixes the FSDAX misdetection for non-block extra blobs.

Fixes: c6993c4cb918 ("erofs: Fallback to normal access if DAX is not supported on extra device")
Reported-by: syzbot+31b8fb02cb8a25bd5e78@...kaller.appspotmail.com
Closes: https://lore.kernel.org/r/691af9f6.a70a0220.3124cb.0097.GAE@google.com
Cc: Yuezhang Mo <Yuezhang.Mo@...y.com>
Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
---
 fs/erofs/super.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index f3f8d8c066e4..cd8ff98c2938 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -174,15 +174,15 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
 		if (!erofs_is_fileio_mode(sbi)) {
 			dif->dax_dev = fs_dax_get_by_bdev(file_bdev(file),
 					&dif->dax_part_off, NULL, NULL);
-			if (!dif->dax_dev && test_opt(&sbi->opt, DAX_ALWAYS)) {
-				erofs_info(sb, "DAX unsupported by %s. Turning off DAX.",
-					   dif->path);
-				clear_opt(&sbi->opt, DAX_ALWAYS);
-			}
 		} else if (!S_ISREG(file_inode(file)->i_mode)) {
 			fput(file);
 			return -EINVAL;
 		}
+		if (!dif->dax_dev && test_opt(&sbi->opt, DAX_ALWAYS)) {
+			erofs_info(sb, "DAX unsupported by %s. Turning off DAX.",
+				   dif->path);
+			clear_opt(&sbi->opt, DAX_ALWAYS);
+		}
 		dif->file = file;
 	}
 
@@ -215,13 +215,13 @@ static int erofs_scan_devices(struct super_block *sb,
 			  ondisk_extradevs, sbi->devs->extra_devices);
 		return -EINVAL;
 	}
-	if (!ondisk_extradevs) {
-		if (test_opt(&sbi->opt, DAX_ALWAYS) && !sbi->dif0.dax_dev) {
-			erofs_info(sb, "DAX unsupported by block device. Turning off DAX.");
-			clear_opt(&sbi->opt, DAX_ALWAYS);
-		}
-		return 0;
+
+	if (test_opt(&sbi->opt, DAX_ALWAYS) && !sbi->dif0.dax_dev) {
+		erofs_info(sb, "DAX unsupported by block device. Turning off DAX.");
+		clear_opt(&sbi->opt, DAX_ALWAYS);
 	}
+	if (!ondisk_extradevs)
+		return 0;
 
 	if (!sbi->devs->extra_devices && !erofs_is_fscache_mode(sb))
 		sbi->devs->flatdev = true;
-- 
2.43.5