On Thu, May 25, 2023 at 04:14:30PM +0200, Jan Kara wrote:
> Yes, this is exactly how I'd imagine it. Thanks for writing the patch!
>
> I'd just note that this would need rebasing on top of Luis' patches 1 and
> 2. Also:
I'd not do that for now. 1 needs a lot more work, and 2 seems rather
questionable.
> Now the only remaining issue with the code is that the two different
> holders can be attempting to freeze the filesystem at once and in that case
> one of them has to wait for the other one instead of returning -EBUSY as
> would happen currently. This can happen because we temporarily drop
> s_umount in freeze_super() due to lock ordering issues. I think we could
> do something like:
>
> if (!sb_unfrozen(sb)) {
> up_write(&sb->s_umount);
> wait_var_event(&sb->s_writers.frozen,
> sb_unfrozen(sb) || sb_frozen(sb));
> down_write(&sb->s_umount);
> goto retry;
> }
>
> and then sprinkle wake_up_var(&sb->s_writers.frozen) at appropriate places
> in freeze_super().
Let's do that separately as a follow on..
>
> BTW, when reading this code, I've spotted attached cleanup opportunity but
> I'll queue that separately so that is JFYI.
>
> > +#define FREEZE_HOLDER_USERSPACE (1U << 1) /* userspace froze fs */
> > +#define FREEZE_HOLDER_KERNEL (1U << 2) /* kernel froze fs */
>
> Why not start from 1U << 0? And bonus points for using BIT() macro :).
BIT() is a nasty thing and actually makes code harder to read. And it
doesn't interact very well with the __bitwise annotation that might
actually be useful here.
