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Message-ID: <9f236f42-8aee-411c-9bd4-d7029c49a0a1@paulmck-laptop>
Date: Wed, 16 Aug 2023 15:54:13 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Julian Anastasov <ja@....bg>
Cc: Simon Horman <horms@...ge.net.au>, lvs-devel@...r.kernel.org,
netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
rcu@...r.kernel.org, Dust Li <dust.li@...ux.alibaba.com>,
Jiejian Wu <jiejian@...ux.alibaba.com>,
Jiri Wiesner <jwiesner@...e.de>
Subject: Re: [PATCH RFC net-next 01/14] rculist_bl: add
hlist_bl_for_each_entry_continue_rcu
On Wed, Aug 16, 2023 at 07:02:39PM +0300, Julian Anastasov wrote:
>
> Hello,
>
> On Tue, 15 Aug 2023, Paul E. McKenney wrote:
>
> > On Tue, Aug 15, 2023 at 08:30:18PM +0300, Julian Anastasov wrote:
> > > Add hlist_bl_for_each_entry_continue_rcu and hlist_bl_next_rcu
> > >
> > > Signed-off-by: Julian Anastasov <ja@....bg>
> > > ---
> > > include/linux/rculist_bl.h | 17 +++++++++++++++++
> > > 1 file changed, 17 insertions(+)
> > >
> > > diff --git a/include/linux/rculist_bl.h b/include/linux/rculist_bl.h
> > > index 0b952d06eb0b..93a757793d83 100644
> > > --- a/include/linux/rculist_bl.h
> > > +++ b/include/linux/rculist_bl.h
> > > @@ -24,6 +24,10 @@ static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
> > > ((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
> > > }
> > >
> > > +/* return the next element in an RCU protected list */
> > > +#define hlist_bl_next_rcu(node) \
> > > + (*((struct hlist_bl_node __rcu **)(&(node)->next)))
> > > +
> > > /**
> > > * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
> > > * @n: the element to delete from the hash list.
> > > @@ -98,4 +102,17 @@ static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
> > > ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
> > > pos = rcu_dereference_raw(pos->next))
> > >
> > > +/**
> > > + * hlist_bl_for_each_entry_continue_rcu - iterate over a list continuing after
> > > + * current point
> >
> > Please add a comment to the effect that the element continued from
> > must have been either: (1) Iterated to within the same RCU read-side
> > critical section or (2) Nailed down using some lock, reference count,
> > or whatever suffices to keep the continued-from element from being freed
> > in the meantime.
>
> I created 2nd version which has more changes. I'm not sure
> what are the desired steps for this patch, should I keep it as part
> of my patchset if accepted? Or should I post it separately? Here it
> is v2 for comments.
This looks plausible to me, but of course needs more eyes and more
testing.
Thanx, Paul
> [PATCHv2 RFC] rculist_bl: add hlist_bl_for_each_entry_continue_rcu
>
> Change the old hlist_bl_first_rcu to hlist_bl_first_rcu_dereference
> to indicate that it is a RCU dereference.
>
> Add hlist_bl_next_rcu and hlist_bl_first_rcu to use RCU pointers
> and use them to fix sparse warnings.
>
> Add hlist_bl_for_each_entry_continue_rcu.
>
> Signed-off-by: Julian Anastasov <ja@....bg>
> ---
> include/linux/rculist_bl.h | 49 +++++++++++++++++++++++++++++++-------
> 1 file changed, 40 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/rculist_bl.h b/include/linux/rculist_bl.h
> index 0b952d06eb0b..36363b876e53 100644
> --- a/include/linux/rculist_bl.h
> +++ b/include/linux/rculist_bl.h
> @@ -8,21 +8,31 @@
> #include <linux/list_bl.h>
> #include <linux/rcupdate.h>
>
> +/* return the first ptr or next element in an RCU protected list */
> +#define hlist_bl_first_rcu(head) \
> + (*((struct hlist_bl_node __rcu **)(&(head)->first)))
> +#define hlist_bl_next_rcu(node) \
> + (*((struct hlist_bl_node __rcu **)(&(node)->next)))
> +
> static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
> struct hlist_bl_node *n)
> {
> LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
> LIST_BL_BUG_ON(((unsigned long)h->first & LIST_BL_LOCKMASK) !=
> LIST_BL_LOCKMASK);
> - rcu_assign_pointer(h->first,
> + rcu_assign_pointer(hlist_bl_first_rcu(h),
> (struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK));
> }
>
> -static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
> -{
> - return (struct hlist_bl_node *)
> - ((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
> -}
> +#define hlist_bl_first_rcu_dereference(head) \
> +({ \
> + struct hlist_bl_head *__head = (head); \
> + \
> + (struct hlist_bl_node *) \
> + ((unsigned long)rcu_dereference_check(hlist_bl_first_rcu(__head), \
> + hlist_bl_is_locked(__head)) & \
> + ~LIST_BL_LOCKMASK); \
> +})
>
> /**
> * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
> @@ -73,7 +83,7 @@ static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
> {
> struct hlist_bl_node *first;
>
> - /* don't need hlist_bl_first_rcu because we're under lock */
> + /* don't need hlist_bl_first_rcu* because we're under lock */
> first = hlist_bl_first(h);
>
> n->next = first;
> @@ -93,9 +103,30 @@ static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
> *
> */
> #define hlist_bl_for_each_entry_rcu(tpos, pos, head, member) \
> - for (pos = hlist_bl_first_rcu(head); \
> + for (pos = hlist_bl_first_rcu_dereference(head); \
> pos && \
> ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
> - pos = rcu_dereference_raw(pos->next))
> + pos = rcu_dereference_raw(hlist_bl_next_rcu(pos)))
> +
> +/**
> + * hlist_bl_for_each_entry_continue_rcu - continue iteration over list of given
> + * type
> + * @tpos: the type * to use as a loop cursor.
> + * @pos: the &struct hlist_bl_node to use as a loop cursor.
> + * @member: the name of the hlist_bl_node within the struct.
> + *
> + * Continue to iterate over list of given type, continuing after
> + * the current position which must have been in the list when the RCU read
> + * lock was taken.
> + * This would typically require either that you obtained the node from a
> + * previous walk of the list in the same RCU read-side critical section, or
> + * that you held some sort of non-RCU reference (such as a reference count)
> + * to keep the node alive *and* in the list.
> + */
> +#define hlist_bl_for_each_entry_continue_rcu(tpos, pos, member) \
> + for (pos = rcu_dereference_raw(hlist_bl_next_rcu(&(tpos)->member)); \
> + pos && \
> + ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
> + pos = rcu_dereference_raw(hlist_bl_next_rcu(pos)))
>
> #endif
> --
> 2.41.0
>
>
> Regards
>
> --
> Julian Anastasov <ja@....bg>
>
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