Re: [PATCH 1/4] fs: Improve filesystem freezing handling

Jan Kara
2012-01-12T23:15:17Z

On Thu 12-01-12 16:57:42, Eric Sandeen wrote:
> On 1/11/12 7:20 PM, Jan Kara wrote:
> > @@ -183,6 +186,13 @@ static struct super_block *alloc_super(struct file_system_type *type)
> > s->s_shrink.seeks = DEFAULT_SEEKS;
> > s->s_shrink.shrink = prune_super;
> > s->s_shrink.batch = 1024;
> > +
> > + init_waitqueue_head(&s->s_writers_wait);
> > +#ifdef CONFIG_SMP
> > + s->s_page_faults = alloc_percpu(int);
>
> isn't this s->s_writers? s->s_page_faults isn't defined anywhere.
Right. Leftover from original implementation and since I was doing
initial testing only using UML, I didn't spot this. Thanks.

> > +#endif
> > + lockdep_init_map(&s->s_writers_lock_map, "sb_writers",
> > + &sb_writers_key, 0);
> > }
> > out:
> > return s;
> > @@ -1126,6 +1136,84 @@ out:
> > }
> >
> > /**
> > + * sb_start_write - drop write access to a superblock
> ^^^^^^^^^^^^^^
>
> s/b sb_end_write
Fixed.

> > @@ -1136,6 +1224,7 @@ out:
> > int freeze_super(struct super_block *sb)
> > {
> > int ret;
> > + int writers;
> >
> > atomic_inc(&sb->s_active);
> > down_write(&sb->s_umount);
> > @@ -1151,8 +1240,36 @@ int freeze_super(struct super_block *sb)
> > return 0;
> > }
> >
> > + rwsem_acquire(&sb->s_writers_lock_map, 0, 0, _THIS_IP_);
> > sb->s_frozen = SB_FREEZE_WRITE;
> > - smp_wmb();
> > + /*
> > + * Now wait for all page faults to finish. ->page_mkwrite()
> > + * implementations must call vfs_check_frozen() before starting
> > + * a fault so that we cannot livelock here. Because of that we
> > + * are guaranteed that from this moment on new ->page_mkwrite()
> > + * calls will block and we just have to wait for s_page_faults
>
> wait for s_writers, right?
Yes. Fixed.

Thanks for review.

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR