On 2011-04-04, at 9:47 PM, Yongqiang Yang wrote:
> handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks)
> {
> + handle = ext4_journal_current_handle();
> +
> + /*
> + * Before vfs_check_frozen(), the current handle should be allowed
> + * to finish, otherwise deadlock would happen when the filesystem
> + * is freezed && active handles are not stopped.
> + */
> + if (!journal) {
> + if (!handle)
> + vfs_check_frozen(sb, SB_FREEZE_TRANS);
> + return ext4_get_nojournal();
> }
> +
> + if (!handle)
> + vfs_check_frozen(sb, SB_FREEZE_TRANS);
This is probably easier to read by putting the !handle check/code together,
with a minor fixup to the comment as well:
/*
* If a handle has already been started, it should be allowed to
* finish, otherwise deadlock could happen between freeze and
* truncate due to the restart of the journal handle if the
* filesystem is frozen and active handles are not stopped.
*/
if (!handle) {
vfs_check_frozen(sb, SB_FREEZE_TRANS);
if (!journal)
return ext4_get_nojournal();
}
/*
* Special case here: if the journal has aborted behind our
* backs (eg. EIO in the commit thread), then we still need to
* take the FS itself readonly cleanly.
*/
if (is_journal_aborted(journal)) {
ext4_abort(sb, "Detected aborted journal");
return ERR_PTR(-EROFS);
}
return jbd2_journal_start(journal, nblocks);
}
> /*
> @@ -4131,6 +4149,11 @@ static int ext4_sync_fs(struct super_block *sb, int wait)
> /*
> * LVM calls this function before a (read-only) snapshot is created. This
> * gives us a chance to flush the journal completely and mark the fs clean.
> + *
> + * Note that only this function cannot bring a filesystem to be in a clean
> + * state independently, because ext4 prevents a new handle from being started
> + * by @sb->s_frozen, which stays in an upper layer. It thus needs help from
> + * the upper layer.
> */
> static int ext4_freeze(struct super_block *sb)
> {
> --
> 1.7.4
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Cheers, Andreas
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