Re: [PATCH 3/4 v2] rculist: add list_for_each_entry_from_rcu()

From: NeilBrown
Date: Tue May 01 2018 - 17:35:18 EST


On Tue, May 01 2018, Paul E. McKenney wrote:

> On Tue, May 01, 2018 at 01:11:29PM +1000, NeilBrown wrote:
>>
>> list_for_each_entry_from_rcu() is an RCU version of
>> list_for_each_entry_from(). It walks a linked list under rcu
>> protection, from a given start point.
>>
>> It is similar to list_for_each_entry_continue_rcu() but starts *at*
>> the given position rather than *after* it.
>>
>> Naturally, the start point must be known to be in the list.
>>
>> Also update the documentation for list_for_each_entry_continue_rcu()
>> to match the documentation for the new list_for_each_entry_from_rcu(),
>> and add list_for_each_entry_from_rcu() and the already existing
>> hlist_for_each_entry_from_rcu() to section 7 of whatisRCU.txt.
>>
>> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
>
> I am guessing that it would be more convenient for you to carry this
> with the patches using it, so:
>
> Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

Thanks Paul,
yes I do hope this patch will go in with the other NFS patches.
I'll wait to see what Trond and Anna think before proceeding with
anything myself.

Thanks a lot,
NeilBrown


>
> If not, please let me know.
>
> Thanx, Paul
>
>> ---
>> Documentation/RCU/whatisRCU.txt | 2 ++
>> include/linux/rculist.h | 32 +++++++++++++++++++++++++++++++-
>> 2 files changed, 33 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
>> index a27fbfb0efb8..b7d38bd212d2 100644
>> --- a/Documentation/RCU/whatisRCU.txt
>> +++ b/Documentation/RCU/whatisRCU.txt
>> @@ -814,11 +814,13 @@ RCU list traversal:
>> list_next_rcu
>> list_for_each_entry_rcu
>> list_for_each_entry_continue_rcu
>> + list_for_each_entry_from_rcu
>> hlist_first_rcu
>> hlist_next_rcu
>> hlist_pprev_rcu
>> hlist_for_each_entry_rcu
>> hlist_for_each_entry_rcu_bh
>> + hlist_for_each_entry_from_rcu
>> hlist_for_each_entry_continue_rcu
>> hlist_for_each_entry_continue_rcu_bh
>> hlist_nulls_first_rcu
>> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
>> index 127f534fec94..4786c2235b98 100644
>> --- a/include/linux/rculist.h
>> +++ b/include/linux/rculist.h
>> @@ -396,13 +396,43 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
>> * @member: the name of the list_head within the struct.
>> *
>> * Continue to iterate over list of given type, continuing after
>> - * the current position.
>> + * 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.
>> + *
>> + * This iterator is similar to list_for_each_entry_from_rcu() except
>> + * this starts after the given position and that one starts at the given
>> + * position.
>> */
>> #define list_for_each_entry_continue_rcu(pos, head, member) \
>> for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \
>> &pos->member != (head); \
>> pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
>>
>> +/**
>> + * list_for_each_entry_from_rcu - iterate over a list from current point
>> + * @pos: the type * to use as a loop cursor.
>> + * @head: the head for your list.
>> + * @member: the name of the list_node within the struct.
>> + *
>> + * Iterate over the tail of a list starting from a given 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.
>> + *
>> + * This iterator is similar to list_for_each_entry_continue_rcu() except
>> + * this starts from the given position and that one starts from the position
>> + * after the given position.
>> + */
>> +#define list_for_each_entry_from_rcu(pos, head, member) \
>> + for (; &(pos)->member != (head); \
>> + pos = list_entry_rcu(pos->member.next, typeof(*(pos)), member))
>> +
>> /**
>> * hlist_del_rcu - deletes entry from hash list without re-initialization
>> * @n: the element to delete from the hash list.
>> --
>> 2.14.0.rc0.dirty
>>

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