Re: [PATCH RFC] Btrfs: expose bad chunks in sysfs

[Liu Bo <bo.li.liu@oracle.com>]

On Mon, Feb 12, 2018 at 07:39:02PM +0200, Nikolay Borisov wrote:
> 
> 
> On 12.02.2018 16:17, Liu Bo wrote:
> > On Tue, Feb 06, 2018 at 11:11:55AM +0200, Nikolay Borisov wrote:
[...]
> >>
> >> Use list_for_each_entry_safe to make it more apparent you are going to
> >> be removing from the list. The code as-is works since you are doing a
> >> break after deleting element from the list but this is somewhat subtle.
> > 
> > To be honest, I don't see much difference.
> > 
> > I think the _safe version is to protect us from some race when others
> > remove objects from list, and write lock is held so we're safe.
> 
> No, the _safe version uses the second argument (n) as the list iterator.
> The non-safe version just uses 'pos', and in case you remove 'pos' from
> the list AND continue iterating you will deref an invalid pointer. So
> _safe is actually really necessary for correctness when you intend to
> remove an entry from a list you are iterating, irrespective of any locks
> you might have.

You're right, I know it takes an extra pointer to store the next
entry, but miss the point when deleting by itself.

Thank you for the clarification.

thanks,
-liubo