| Message ID | 20150811170404.GA26911@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue 11-08-15 19:04:04, Oleg Nesterov wrote: > 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 <oleg@redhat.com> Looks good. You can add: Reviewed-by: Jan Kara <jack@suse.com> Honza > --- > fs/super.c | 12 +++++++++--- > 1 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/fs/super.c b/fs/super.c > index d0fdd49..89b58fb 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 { > -- > 1.5.5.1 >
diff --git a/fs/super.c b/fs/super.c index d0fdd49..89b58fb 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 {
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 <oleg@redhat.com> --- fs/super.c | 12 +++++++++--- 1 files changed, 9 insertions(+), 3 deletions(-)