linux-kernel - Re: [PATCH 17/46] fs: Use rename lock and RCU for multi-step operations

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Date:	Thu, 27 Jan 2011 16:18:25 +1100
From:	Nick Piggin <npiggin@...il.com>
To:	Yehuda Sadeh Weinraub <yehudasa@...il.com>
Cc:	Nick Piggin <npiggin@...nel.dk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Sage Weil <sage@...dream.net>,
	ceph-devel@...r.kernel.org
Subject: Re: [PATCH 17/46] fs: Use rename lock and RCU for multi-step operations

On Wed, Jan 26, 2011 at 9:10 AM, Yehuda Sadeh Weinraub
<yehudasa@...il.com> wrote:
> On Wed, Jan 19, 2011 at 2:32 PM, Nick Piggin <npiggin@...il.com> wrote:
>> On Thu, Jan 20, 2011 at 9:27 AM, Yehuda Sadeh Weinraub
>> <yehudasa@...il.com> wrote:
>>> On Tue, Jan 18, 2011 at 2:42 PM, Nick Piggin <npiggin@...il.com> wrote:
>>>> On Wed, Jan 19, 2011 at 9:32 AM, Yehuda Sadeh Weinraub
>>>
>>>>> There's an issue with ceph as it references the
>>>>> dentry->d_parent(->d_inode) at dentry_release(), so setting
>>>>> dentry->d_parent to NULL here doesn't work with ceph. Though there is
>>>>> some workaround for it, we would like to be sure that this one is
>>>>> really required so that we don't exacerbate the ugliness. The
>>>>> workaround is to keep a pointer to the parent inode in the private
>>>>> dentry structure, which will be referenced only at the .release()
>>>>> callback. This is clearly not ideal.
>>>>
>>>> Hmm, I'll have to think about it. Probably we can check for
>>>> d_count == 0 rather than parent != NULL I think?
>>>>
>>>
>>> That'll solve ceph's problem, don't know about how'd affect other
>>> stuff. We'll need to know whether this is the solution, or whether
>>> we'd need to introduce some other band aid fix.
>>
>> No I think it will work fine. Basically we just need to know whether
>> we have been deleted, and if so then we restart rather than walking
>> back up the parent.
>>
>> I'll send a patch in a few days. For the meantime, it's a rathe
>> small window for ceph to worry about. So we'll have something
>> before -rc2 which should be OK.
>>
>
> I guess that it's a bit late for -rc2, should we assume that it'll be on -rc3?

Yeah, I'm sorry I've been travelling and a bit disconnected.

NFS folk are having a similar problem and looks like similar
proposed fix will do it.

http://marc.info/?l=linux-fsdevel&m=129599823927039&w=2

So I think it is the best way to go to restore behaviour back to what
filesystems already expect, to avoid more surprises in future.

Thanks,
Nick
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