On Mon, Jun 22, 2020 at 07:50:56PM +0200, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
From 829b37b8cddb1db75c1b7905505b90e593b15db1 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso@xxxxxxx>
Date: Wed, 10 Jun 2020 11:16:37 -0400
Subject: [PATCH] ext4: avoid race conditions when remounting with options that
change dax
Trying to change dax mount options when remounting could allow mount
options to be enabled for a small amount of time, and then the mount
option change would be reverted.
In the case of "mount -o remount,dax", this can cause a race where
files would temporarily treated as DAX --- and then not.
Cc: stable@xxxxxxxxxx
Reported-by: syzbot+bca9799bf129256190da@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
We didn't have the conversion of the DAX mount option to a tri-state back in
5.7 and older:
9cb20f94afcd ("fs/ext4: Make DAX mount option a tri-state")
a8ab6d3885ef ("fs/ext4: Update ext4_should_use_dax()")
fc626fe322f1 ("fs/ext4: Change EXT4_MOUNT_DAX to EXT4_MOUNT_DAX_ALWAYS")
I think that something like this (untested) patch should work:
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d23afd6c909de..7318ca71b69eb 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2080,6 +2080,16 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
#endif
} else if (token == Opt_dax) {
#ifdef CONFIG_FS_DAX
+ if (is_remount && test_opt(sb, DAX)) {
+ ext4_msg(sb, KERN_ERR, "can't mount with "
+ "both data=journal and dax");
+ return -1;
+ }
+ if (is_remount && !(sbi->s_mount_opt & EXT4_MOUNT_DAX)) {
+ ext4_msg(sb, KERN_ERR, "can't change "
+ "dax mount option while remounting");
+ return -1;
+ }
ext4_msg(sb, KERN_WARNING,
"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
sbi->s_mount_opt |= m->mount_opt;
@@ -5407,12 +5417,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
err = -EINVAL;
goto restore_opts;
}
- if (test_opt(sb, DAX)) {
- ext4_msg(sb, KERN_ERR, "can't mount with "
- "both data=journal and dax");
- err = -EINVAL;
- goto restore_opts;
- }
} else if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_ORDERED_DATA) {
if (test_opt(sb, JOURNAL_ASYNC_COMMIT)) {
ext4_msg(sb, KERN_ERR, "can't mount with "
@@ -5428,12 +5432,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
goto restore_opts;
}
- if ((sbi->s_mount_opt ^ old_opts.s_mount_opt) & EXT4_MOUNT_DAX) {
- ext4_msg(sb, KERN_WARNING, "warning: refusing change of "
- "dax flag with busy inodes while remounting");
- sbi->s_mount_opt ^= EXT4_MOUNT_DAX;
- }
-
if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED)
ext4_abort(sb, EXT4_ERR_ESHUTDOWN, "Abort forced by user");
--
Thanks,
Sasha
