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

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Date:	Mon, 7 Feb 2011 15:25:54 -0700
From:	"Jim Schutt" <jaschut@...dia.gov>
To:	"Yehuda Sadeh Weinraub" <yehudasa@...il.com>
cc:	"Nick Piggin" <npiggin@...il.com>,
	"Nick Piggin" <npiggin@...nel.dk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Sage Weil" <sage@...dream.net>,
	"ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>
Subject: Re: [PATCH 17/46] fs: Use rename lock and RCU for multi-step
 operations


On Mon, 2011-02-07 at 14:04 -0700, Yehuda Sadeh Weinraub wrote:
> On Mon, Feb 7, 2011 at 10:52 AM, Jim Schutt <jaschut@...dia.gov> wrote:
> >
> > On Wed, 2011-01-26 at 22:18 -0700, Nick Piggin wrote:
> >> 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.
> >
> > I think the following BUG indicates I'm hitting this problem?
> > All I have to do to cause it is unlink a file.
> >
> > My ceph client kernel is 8dbdea8444 (master branch) from
> >  git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
> > + e41cdbb6c5 (master branch) + a3f5274e53 (unstable branch)
> >  from git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client.git
> >
> > Are there any patches available for this I can test?
> >
> > Thanks -- Jim
> >
> 
> It does look like this specific problem.
> You can try cherry-pick commit 9c3db35 off the ceph git. It is just a
> temporary workaround, and it wasn't tested too much. Hopefully Nick
> will push his fix soon so that it wouldn't be needed.


That commit fixes my unlink issue, thanks.
I'm happy to use it while things get resolved.

-- Jim

> 
> Thanks,
> Yehuda
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