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author | Yongqiang Yang <xiaoqiangnk@gmail.com> | 2011-04-10 22:06:07 -0400 |
---|---|---|
committer | Theodore Ts'o <tytso@mit.edu> | 2011-04-10 22:06:07 -0400 |
commit | be4f27d324e8ddd57cc0d4d604fe85ee0425cba9 (patch) | |
tree | e4262a9e1ade9095e1bf937dc4b9d56a08824eda /fs/ext4/super.c | |
parent | 0893ed458b4b1d7c7667ca7ffb8b11febe7e7e6c (diff) | |
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ext4: allow an active handle to be started when freezing
ext4_journal_start_sb() should not prevent an active handle from being
started due to s_frozen. Otherwise, deadlock is easy to happen, below
is a situation.
================================================
freeze | truncate
================================================
| ext4_ext_truncate()
freeze_super() | starts a handle
sets s_frozen |
| ext4_ext_truncate()
| holds i_data_sem
ext4_freeze() |
waits for updates |
| ext4_free_blocks()
| calls dquot_free_block()
|
| dquot_free_blocks()
| calls ext4_dirty_inode()
|
| ext4_dirty_inode()
| trys to start an active
| handle
|
| block due to s_frozen
================================================
Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reported-by: Amir Goldstein <amir73il@users.sf.net>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Diffstat (limited to 'fs/ext4/super.c')
-rw-r--r-- | fs/ext4/super.c | 44 |
1 files changed, 33 insertions, 11 deletions
diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 551cb8e..7b636ce 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -242,27 +242,44 @@ 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); + handle = ext4_journal_current_handle(); + + /* + * If a handle has been started, it should be allowed to + * finish, otherwise deadlock could happen between freeze + * and others(e.g. truncate) due to the restart of the + * journal handle if the filesystem is forzen 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 ext4_get_nojournal(); + return jbd2_journal_start(journal, nblocks); } /* @@ -4146,6 +4163,11 @@ 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) { |