From: Oleg Nesterov Date: Tue, 11 Aug 2015 14:28:29 +0000 (+0200) Subject: document rwsem_release() in sb_wait_write() X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=0e28e01f1e73015d8e1b8fa1cda071d0bd9a2600;p=openwrt%2Fstaging%2Fblogic.git document rwsem_release() in sb_wait_write() Not only we need to avoid the warning from lockdep_sys_exit(), the caller of freeze_super() can never release this lock. Another thread can do this, so there is another reason for rwsem_release(). Plus the comment should explain why we have to fool lockdep. Signed-off-by: Oleg Nesterov Reviewed-by: Jan Kara --- diff --git a/fs/super.c b/fs/super.c index 24a76bcd62a5..8aa3cbc571d1 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1236,11 +1236,17 @@ static void sb_wait_write(struct super_block *sb, int level) { s64 writers; + rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_); /* - * We just cycle-through lockdep here so that it does not complain - * about returning with lock to userspace + * We are going to return to userspace and forget about this lock, the + * ownership goes to the caller of thaw_super() which does unlock. + * + * FIXME: we should do this before return from freeze_super() after we + * called sync_filesystem(sb) and s_op->freeze_fs(sb), and thaw_super() + * should re-acquire these locks before s_op->unfreeze_fs(sb). However + * this leads to lockdep false-positives, so currently we do the early + * release right after acquire. */ - rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_); rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_); do {