On Fri, Jun 11, 2010 at 7:50 AM, Nick Piggin <npiggin@xxxxxxx> wrote:
> Not sure if this is really the _cleanest_ way to fix it. But open coding
> the list walking is a bit annoying too. And I couldn't see any real way to
> make the list macro safe. Better ideas?
I really think we should open-code the list walking instead. You
basically already are doing that, and in a very non-obvious way too
(ie you are mixing the non-open-coded list walker with also explicitly
playing with the internal variable for that magic walker.
So I would get rid of the 'list_for_each_entry_safe' entirely, and
replace it with something like
struct list_head *list;
spin_lock(&sb_lock);
list = super_blocks->next;
while (list != &super_blocks) {
struct super_block *sb = list_entry(next, struct super_block, s_list);
list = list->next;
if (list_empty(&sb->s_instances))
continue;
if (!sb->s_nr_dentry_unused)
continue;
sb->s_count++;
spin_unlock(&sb_lock);
.... whatever ...
spin_lock(&sb_lock);
/* We dropped the lock, need to re-load the next list entry */
list = sb->s_list.next;
__put_super(sb);
}
which isn't that much more complicated, now is it? Sure, it's
open-coded, but at least it doesn't play games. And being open-coded,
it's a lot more honest about the issue. Maybe even add a comment
saying "we can't use the list_for_each[_safe]() macro, because we
don't hold the lock and we're not the only ones that may delete
things" explaining _why_ it's open-coded.
I dunno. Maybe Al disagrees. I just don't like using the "simple
helpers" and then changing subtly how they work by knowing their
internals.
Linus
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