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From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>, NeilBrown <neilb@suse.com>,
	Trond Myklebust <trond.myklebust@primarydata.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	linux-nfs@vger.kernel.org, Lai Jiangshan <jiangshanlai@gmail.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] rculist: add list_for_each_entry_from_rcu()
Date: Mon, 30 Apr 2018 11:14:54 -0400	[thread overview]
Message-ID: <20180430111454.722c2aa8@gandalf.local.home> (raw)
In-Reply-To: <20180430134308.GT26088@linux.vnet.ibm.com>

On Mon, 30 Apr 2018 06:43:08 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> On Sun, Apr 29, 2018 at 10:20:33PM -0700, Josh Triplett wrote:
> > On Mon, Apr 30, 2018 at 02:31:30PM +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.  
> > 
> > I'd suggest giving an explicit advisory comment to clarify and suggest
> > correct usage:
> > 
> > "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."
> > 
> > (Feel free to wordsmith the exact wording, but something like that seems
> > like it would help people understand how to use this correctly, and make
> > it less likely that they'd use it incorrectly.)  
> 
> What Josh said!  Could you also contrast this with the existing
> list_for_each_entry_continue_rcu() macro in the header comment as well
> as in the commit log?
> 

Should Documentation/RCU/whatisRCU.txt be updated?

Specifically section: 7.  FULL LIST OF RCU APIs

-- Steve

  reply	other threads:[~2018-04-30 15:15 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-30  4:31 [PATCH 0/4 V2] Avoid quadratic search when freeing delegations NeilBrown
2018-04-30  4:31 ` [PATCH 3/4] rculist: add list_for_each_entry_from_rcu() NeilBrown
2018-04-30  5:20   ` Josh Triplett
2018-04-30 13:43     ` Paul E. McKenney
2018-04-30 15:14       ` Steven Rostedt [this message]
2018-04-30 15:35         ` Paul E. McKenney
2018-05-01  3:11           ` [PATCH 3/4 v2] " NeilBrown
2018-05-01 14:14             ` Paul E. McKenney
2018-05-01 21:34               ` NeilBrown
2018-04-30  4:31 ` [PATCH 1/4] NFS: slight optimization for walking list for delegations NeilBrown
2018-04-30 15:17   ` Steven Rostedt
2018-05-31  5:23     ` [PATCH 1/4 v2] " NeilBrown
2018-06-04 21:31       ` Steven Rostedt
2018-04-30  4:31 ` [PATCH 2/4] NFS: use cond_resched() when restarting walk of delegation list NeilBrown
2018-04-30  4:31 ` [PATCH 4/4] NFS: Avoid quadratic search when freeing delegations NeilBrown

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