linux-kernel - Re: [PATCH 3/4 v2] rculist: add list_for_each_entry_from

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Date:   Wed, 02 May 2018 07:34:56 +1000
From:   NeilBrown <neilb@...e.com>
To:     paulmck@...ux.vnet.ibm.com
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        linux-nfs@...r.kernel.org, Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4 v2] rculist: add list_for_each_entry_from_rcu()

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@...e.com>
>
> 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@...ux.vnet.ibm.com>

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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