linux-kernel - Re: [PATCH 04/24] sysfs: Normalize removing sysfs directories.

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Date:	Sat, 30 May 2009 19:43:59 +0900
From:	Tejun Heo <tj@...nel.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-kernel@...r.kernel.org,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	linux-fsdevel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>,
	Greg KH <greg@...ah.com>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH 04/24] sysfs: Normalize removing sysfs directories.

Eric W. Biederman wrote:
>   Also, I'm quite uncomfortable with these things
>> being done in non-atomic manner.  It can be made to work but things
>> like this can lead to subtle race conditions and with the kind of
>> layering we put on top of sysfs (kobject, driver model, driver
>> midlayers and so on), it isn't all that easy to verify what's going
>> on, so NACK for this one.
> 
> Total nonsense.
> 
> Mucking about with sysfs after we start deleting a directory is a bug.
> At worst my change makes a buggy race slightly less deterministic.
> 
> I am not ready to consider keeping the current unnecessary atomic
> removal step.  That unnecessary atomicity makes the following patches
> more difficult, and requires a lot of unnecessary retesting.
> 
> What do you think the extra unnecessary atomicity helps protect?

It's just not a clean API.  When people are trying to code things way
up in the stack, they aren't likely to look up the code to see what
assumptions are being made especially when the stack is deep and
complex and sysfs is near the bottom of the tall stack.  IMHO
implementing the usually expected semantics at this depth is worth
every effort.  It's just good implementation style which might look
like wasted effort but will harden the stack in the long run.  Plus,
it's not like making it atomic is difficult or anything.

So, still NACK.

Thanks.

-- 
tejun
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