From: Aristeu Rozanski <aris@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
Li Zefan <lizefan@huawei.com>, Hillf Danton <dhillf@gmail.com>,
Lennart Poettering <lpoetter@redhat.com>
Subject: Re: [PATCH v6 1/4] xattr: extract simple_xattr code from tmpfs
Date: Wed, 22 Aug 2012 16:55:57 -0400 [thread overview]
Message-ID: <20120822205556.GE16951@redhat.com> (raw)
In-Reply-To: <alpine.LSU.2.00.1208221312540.1909@eggly.anvils>
On Wed, Aug 22, 2012 at 01:25:06PM -0700, Hugh Dickins wrote:
> > > Probably more important would be to remove spin_lock() and spin_unlock()
> > > (and INIT_LIST_HEAD) from simple_xattrs_free() - those are unnecessary
> > > in shmem_evict_inode(), and wouldn't they be unnecessary whenever
> > > simple_xattrs_free() gets called?
> >
> > Removing INIT_LIST_HEAD() it's possible by actually unlinking each xattr
> > inside the loop before freeing them. still, it'll have to check if the list is
> > empty or not, which might end up being the same?
> >
> > About the locking, I'm not sure, I'm investigating it.
>
> I think we have a misunderstanding.
>
> INIT_LIST_HEAD() is not expensive, I just meant to remove it because
> I thought it unnecessary by that point.
ah, I see.
> Do you envisage anywhere that would call simple_xattrs_free() except
> a filesystem's evict_inode()?
cgroup does it differently and it's called in d_iput() path (see cgroup_diput),
because it needs to selectively remove files upon remount.
> By that point, the inode is on its way out of the system: nothing
> much (yes, I am being a bit vague there ;) can get to it any more,
> there's no need to reinitialize the list head and there's no need for
> locking, because nothing else can be playing with those xattrs now.
I agree with you. That's why I'm looking into it because I'm pretty sure
I removed it at some point in the past and decided to put it back after
investigating the easily reproducible oops. Sadly I managed to forget
the analisys I did at the time.
--
Aristeu
next prev parent reply other threads:[~2012-08-22 20:56 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-16 17:44 [PATCH v6 0/4] cgroup: add xattr support aris
2012-08-16 17:44 ` [PATCH v6 1/4] xattr: extract simple_xattr code from tmpfs aris
2012-08-16 19:58 ` Tejun Heo
2012-08-20 7:10 ` Hugh Dickins
2012-08-20 19:00 ` Aristeu Rozanski
2012-08-21 4:47 ` Hugh Dickins
2012-08-22 20:07 ` Aristeu Rozanski
2012-08-22 20:25 ` Hugh Dickins
2012-08-22 20:55 ` Aristeu Rozanski [this message]
2012-08-16 17:44 ` [PATCH v6 2/4] cgroup: revise how we re-populate root directory aris
2012-08-16 17:44 ` [PATCH v6 3/4] cgroup: add xattr support aris
2012-08-16 20:00 ` Tejun Heo
2012-08-21 21:43 ` Lennart Poettering
2012-08-21 21:48 ` Tejun Heo
2012-08-21 23:29 ` Hugh Dickins
2012-08-23 19:44 ` Tejun Heo
2012-08-23 19:58 ` Aristeu Rozanski
2012-08-24 0:02 ` Eric W. Biederman
2012-08-16 17:44 ` [PATCH v6 4/4] cgroup: rename subsys_bits to subsys_mask aris
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