On Sat, Sep 21, 2019 at 12:12:33AM +0100, Al Viro wrote:
> Neither hlist_add_before() nor hlist_add_behind() should ever
> be called with both arguments pointing to the same hlist_node.
> However, gcc doesn't know that, so it ends up with pointless reloads.
> AFAICS, the following generates better code, is obviously equivalent
> in case when arguments are different and actually even in case when
> they are same, the end result is identical (if the hlist hadn't been
> corrupted even earlier than that).
>
> Objections?
>
> Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
*gyah*
git diff >/tmp/y1
<build>
<fix a braino>
<test>
scp-out /tmp/y1
<send mail with the original diff>
<several hours later: reread the sent mail>
My apologies ;-/ Correct diff follows:
diff --git a/include/linux/list.h b/include/linux/list.h
index 85c92555e31f..5c84383675bc 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -793,21 +793,21 @@ static inline void hlist_add_head(struct hlist_node *n,
struct hlist_head *h)
static inline void hlist_add_before(struct hlist_node *n,
struct hlist_node *next)
{
- n->pprev = next->pprev;
+ struct hlist_node **p = n->pprev = next->pprev;
n->next = next;
next->pprev = &n->next;
- WRITE_ONCE(*(n->pprev), n);
+ WRITE_ONCE(*p, n);
}
static inline void hlist_add_behind(struct hlist_node *n,
struct hlist_node *prev)
{
- n->next = prev->next;
+ struct hlist_node *p = n->next = prev->next;
prev->next = n;
n->pprev = &prev->next;
- if (n->next)
- n->next->pprev = &n->next;
+ if (p)
+ p->pprev = &n->next;
}
/* after that we'll appear to be on some hlist and hlist_del will work */
