linux-kernel - Re: [54/94] sunrpc: clarify comments on rpc_make

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Message-ID: <87ehcrqtdn.fsf@canonical.com>
Date:	Tue, 28 May 2013 11:41:08 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	Ben Hutchings <ben@...adent.org.uk>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, akpm@...ux-foundation.org,
	"Trond Myklebust" <Trond.Myklebust@...app.com>
Subject: Re: [54/94] sunrpc: clarify comments on rpc_make_runnable

Jeff Layton <jlayton@...hat.com> writes:

> On Tue, 28 May 2013 04:49:53 +0100
> Ben Hutchings <ben@...adent.org.uk> wrote:
>
>> 3.2.46-rc1 review patch.  If anyone has any objections, please let me know.
>> 
>> ------------------
>> 
>> From: Jeff Layton <jlayton@...hat.com>
>> 
>> commit 506026c3ec270e18402f0c9d33fee37482c23861 upstream.
>> 
>> rpc_make_runnable is not generally called with the queue lock held, unless
>> it's waking up a task that has been sitting on a waitqueue. This is safe
>> when the task has not entered the FSM yet, but the comments don't really
>> spell this out.
>> 
>> Signed-off-by: Jeff Layton <jlayton@...hat.com>
>> Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
>> Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
>> ---
>>  net/sunrpc/sched.c |    5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>> 
>> --- a/net/sunrpc/sched.c
>> +++ b/net/sunrpc/sched.c
>> @@ -296,8 +296,9 @@ EXPORT_SYMBOL_GPL(__rpc_wait_for_complet
>>  /*
>>   * Make an RPC task runnable.
>>   *
>> - * Note: If the task is ASYNC, this must be called with
>> - * the spinlock held to protect the wait queue operation.
>> + * Note: If the task is ASYNC, and is being made runnable after sitting on an
>> + * rpc_wait_queue, this must be called with the queue spinlock held to protect
>> + * the wait queue operation.
>>   */
>>  static void rpc_make_runnable(struct rpc_task *task)
>>  {
>> 
>
> Just a comment patch, so this is harmless and I have no objection but
> why pull it into stable? I had always thought stable-kernel-rules.txt
> discouraged taking patches that don't fix real bugs...

I believe the reason Ben took this patch is actually to provide the
correct context for the next one:

a3c3cac5d31879cd9ae2de7874dc6544ca704aec, "SUNRPC: Prevent an rpc_task wakeup race"

So that this is a clean cherry-pick.

(At least this was the reason I picked it for the 3.5 kernel.)

Cheers,
-- 
Luis
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