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 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html