erofs: Fallback to normal access if DAX is not supported on extra device

[ Upstream commit c6993c4 ]

If using multiple devices, we should check if the extra device support
DAX instead of checking the primary device when deciding if to use DAX
to access a file.

If an extra device does not support DAX we should fallback to normal
access otherwise the data on that device will be inaccessible.

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Reviewed-by: Friendy Su <friendy.su@sony.com>
Reviewed-by: Jacky Cao <jacky.cao@sony.com>
Reviewed-by: Daniel Palmer <daniel.palmer@sony.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Hongbo Li <lihongbo22@huawei.com>
Link: https://lore.kernel.org/r/20250804082030.3667257-2-Yuezhang.Mo@sony.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: YuezhangMo

fs/erofs/super.c

@@ -174,6 +174,11 @@ 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;
@@ -210,8 +215,13 @@ static int erofs_scan_devices(struct super_block *sb,
 			  ondisk_extradevs, sbi->devs->extra_devices);
 		return -EINVAL;
 	}
-	if (!ondisk_extradevs)
+	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 (!sbi->devs->extra_devices && !erofs_is_fscache_mode(sb))
 		sbi->devs->flatdev = true;
@@ -330,7 +340,6 @@ static int erofs_read_superblock(struct super_block *sb)
 	if (ret < 0)
 		goto out;
 
-	/* handle multiple devices */
 	ret = erofs_scan_devices(sb, dsb);
 
 	if (erofs_sb_has_48bit(sbi))
@@ -661,14 +670,9 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 			return invalfc(fc, "cannot use fsoffset in fscache mode");
 	}
 
-	if (test_opt(&sbi->opt, DAX_ALWAYS)) {
-		if (!sbi->dif0.dax_dev) {
-			errorfc(fc, "DAX unsupported by block device. Turning off DAX.");
-			clear_opt(&sbi->opt, DAX_ALWAYS);
-		} else if (sbi->blkszbits != PAGE_SHIFT) {
-			errorfc(fc, "unsupported blocksize for DAX");
-			clear_opt(&sbi->opt, DAX_ALWAYS);
-		}
+	if (test_opt(&sbi->opt, DAX_ALWAYS) && sbi->blkszbits != PAGE_SHIFT) {
+		erofs_info(sb, "unsupported blocksize for DAX");
+		clear_opt(&sbi->opt, DAX_ALWAYS);
 	}
 
 	sb->s_time_gran = 1;