On Mon, Apr 4, 2011 at 10:09 PM, Jan Kara <jack@xxxxxxx> wrote:
> On Mon 04-04-11 20:31:41, Yongqiang Yang wrote:
>> >> Reported-by: Amir Goldstein <amir73il@xxxxxxxxxxxx>
>> >> Signed-off-by: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
>> >> ---
>> >> fs/ext4/super.c | 49 ++++++++++++++++++++++++++++++++++++++-----------
>> >> 1 files changed, 38 insertions(+), 11 deletions(-)
>> >>
>> >> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> >> index ccfa686..f35b53e 100644
>> >> --- a/fs/ext4/super.c
>> >> +++ b/fs/ext4/super.c
>> >> @@ -242,27 +242,49 @@ static void ext4_put_nojournal(handle_t *handle)
>> >> * journal_end calls result in the superblock being marked dirty, so
>> >> * that sync() will call the filesystem's write_super callback if
>> >> * appropriate.
>> >> + *
>> >> + * To avoid j_barrier hold in userspace when a user calls freeze(),
>> >> + * ext4 prevents a new handle from being started by s_frozen, which
>> >> + * is in an upper layer.
>> >> */
>> >> handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks)
>> >> {
>> >> journal_t *journal;
>> >> + handle_t *handle;
>> >>
>> >> if (sb->s_flags & MS_RDONLY)
>> >> return ERR_PTR(-EROFS);
>> >>
>> >> - vfs_check_frozen(sb, SB_FREEZE_TRANS);
>> >> - /* 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. */
>> >> journal = EXT4_SB(sb)->s_journal;
>> >> - if (journal) {
>> >> - if (is_journal_aborted(journal)) {
>> >> - ext4_abort(sb, "Detected aborted journal");
>> >> - return ERR_PTR(-EROFS);
>> >> - }
>> >> - return jbd2_journal_start(journal, nblocks);
>> >> + if (!journal)
>> >> + /*
>> >> + * Under no-journal mode, vfs_check_frozen() is not neeed.
>> >> + */
>> > Why is this? Previously we waited also in the nojournal case and I don't
>> > see anything that would stop modifications in the nojournal case after your
>> > change...
>>
>> I think that ext4 in the nojournal case should do as filesystems
>> without journal, such as ext2. ext4_ext_truncate() upwrite
> But ext2 does not support filesystem freezing...
>
>> i_data_sem only if ext4_journal_extend() fails before
>> ext4_journal_restart() is called, ext4_journal_extend() however always
>> succeeds in nojournal case.
> OK, but again, I'm failing to see how i_data_sem behavior is relevant
> for waiting if a filesystem is frozen... So to be clear I believe we must
> do vfs_check_frozen() even in nojournal case if and only if the handle
> reference count is 0 (it's stored directly in current->journal_info in
> nojournal mode).
My ignorance, I made analysis on i_data_sem under the assumption that
ext3 supports filesystem freezing.
>
> Honza
> --
> Jan Kara <jack@xxxxxxx>
> SUSE Labs, CR
>
--
Best Wishes
Yongqiang Yang
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