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ext4: avoid race conditions when remounting with options that change dax

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[ Upstream commit 829b37b8cddb1db75c1b7905505b90e593b15db1 ]

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: [email protected]
Reported-by: [email protected]
Signed-off-by: Theodore Ts'o <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Theodore Ts'o 2020-06-10 11:16:37 -04:00 • committed by Greg Kroah-Hartman
commit ffa9206a62
1 changed files with 10 additions and 12 deletions
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22
fs/ext4/super.c
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@ -2034,6 +2034,16 @@ 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;
@ -5367,12 +5377,6 @@ 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 "
@ -5388,12 +5392,6 @@ 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, "Abort forced by user");