linux-kernel - Re: [PATCH 1/2] list: introduce a new cutting helper

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Date: Thu, 13 Jun 2024 10:10:16 +0200
From: Christoph Hellwig <hch@....de>
To: Nilay Shroff <nilay@...ux.ibm.com>
Cc: Keith Busch <kbusch@...a.com>, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	hch@....de, sagi@...mberg.me, paulmck@...nel.org,
	davidgow@...gle.com, akpm@...ux-foundation.org,
	venkat88@...ux.vnet.ibm.com, Keith Busch <kbusch@...nel.org>
Subject: Re: [PATCH 1/2] list: introduce a new cutting helper

On Thu, Jun 13, 2024 at 10:26:11AM +0530, Nilay Shroff wrote:
> I am wondering whether we really need the _rcu version of list_cut here?
> I think that @head could point to an _rcu protected list and that's true 
> for this patch. So there might be concurrent readers accessing @head using
> _rcu list-traversal primitives, such as list_for_each_entry_rcu().

Yes, I can't see how this works for a RCU lists without very careful
memory ordering.

Btw, another thing - the old vs new list ordering is reversed vs
list_splice*, which is a bit confusing (as are the parameter names
both for list_splice* and this new helper).  Can you switch them
around to match?