From: Dave Chinner <david@fromorbit.com>
To: Guo Chao <yan@linux.vnet.ibm.com>
Cc: viro@zeniv.linux.org.uk, dchinner@redhat.com, hch@infradead.org,
jack@suse.cz, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v4 Patch 0/4] fs/inode.c: optimization for inode lock usage
Date: Sat, 22 Sep 2012 08:49:12 +1000 [thread overview]
Message-ID: <20120921224912.GA20960@dastard> (raw)
In-Reply-To: <1348219866-1799-1-git-send-email-yan@linux.vnet.ibm.com>
On Fri, Sep 21, 2012 at 05:31:02PM +0800, Guo Chao wrote:
> This patchset optimizes several places which take the per inode spin lock.
> They have not been fully tested yet, thus they are marked as RFC.
Inodes are RCU freed. The i_lock spinlock on the i_state field forms
part of the memory barrier that allows the RCU read side to
correctly detect a freed inode during a RCU protected cache lookup
(hash list traversal for the VFS, or a radix tree traversal for XFS).
The i_lock usage around the hahs list operations ensures the hash
list operations are atomic with state changes so that such changes
are correctly detected during RCU-protected traversals...
IOWs, removing the i_lock from around the i_state transitions and
inode hash insert/remove/traversal operations will cause races in
the RCU lookups and result in incorrectly using freed inodes instead
of failing the lookup and creating a new one.
So I don't think this is a good idea at all...
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2012-09-21 22:49 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-21 9:31 [RFC v4 Patch 0/4] fs/inode.c: optimization for inode lock usage Guo Chao
2012-09-21 9:31 ` [PATCH 1/4] fs/inode.c: do not take i_lock on newly allocated inode Guo Chao
2012-09-21 9:31 ` [PATCH 2/4] fs/inode.c: do not take i_lock in __(insert|remove)_inode_hash Guo Chao
2012-09-21 9:31 ` [PATCH 3/4] fs/inode.c: do not take i_lock when identify an inode Guo Chao
2012-09-21 9:31 ` [PATCH 4/4] fs/inode.c: always take i_lock before calling filesystem's test() method Guo Chao
2012-09-21 12:17 ` [RFC v4 Patch 0/4] fs/inode.c: optimization for inode lock usage Matthew Wilcox
2012-09-21 22:49 ` Dave Chinner [this message]
2012-09-24 2:42 ` Guo Chao
2012-09-24 4:23 ` Dave Chinner
2012-09-24 6:12 ` Guo Chao
2012-09-24 6:28 ` Dave Chinner
2012-09-24 7:08 ` Guo Chao
2012-09-24 8:26 ` Dave Chinner
2012-09-25 8:59 ` Guo Chao
2012-09-26 0:54 ` Dave Chinner
2012-09-27 8:41 ` Guo Chao
2012-09-27 11:51 ` Dave Chinner
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