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Re: 2.6.xx: NFS: directory motion/cam2 contains a readdir loop

To: Bryan Schumaker <bjschuma@xxxxxxxxxx>
Subject: Re: 2.6.xx: NFS: directory motion/cam2 contains a readdir loop
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 27 Jul 2011 16:05:50 -0400
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx>, "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, linux-nfs@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20110727200240.GA16054@xxxxxxxxxxxxx>
References: <alpine.DEB.2.02.1107270952270.1451@xxxxxxxxxxxxxxxx> <20110727160752.GC974@xxxxxxxxxxxx> <alpine.DEB.2.02.1107271227340.1451@xxxxxxxxxxxxxxxx> <20110727181111.GA23009@xxxxxxxxxxxxx> <alpine.DEB.2.02.1107271530340.1451@xxxxxxxxxxxxxxxx> <20110727193937.GA5354@xxxxxxxxxxxxx> <alpine.DEB.2.02.1107271540100.1451@xxxxxxxxxxxxxxxx> <20110727194722.GA9345@xxxxxxxxxxxxx> <4E306D09.5030704@xxxxxxxxxx> <20110727200240.GA16054@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Jul 27, 2011 at 04:02:40PM -0400, Christoph Hellwig wrote:
> But looking closer at it it only prints the directory name and not that
> of any of the matching cookies, making it pretty useless to debug any
> problem.  (and it makes my previous question to Justin look stupid..).
> 
> 
> But so far I still stick to my previous theory that this sounds like
> a directory offset getting reused.  How is cache invalidation for
> the array supposed to work?  And maybe more importantly, given that he
> can only reproduce it with a .38 client did any bugs get fixed in that
> code recently that might lead to issues with the cache invalidation?

Actually we won't even need cache invalidation bugs, see
nfsd_buffered_readdir() - we might do multiple vfs_readdir calls to
fill a single nfs reply, and between these two directory contents might
have been completely replaced, in the worst (pathological case) you
might get a second readdir having exactly the same offsets, but pointing
to completely different inodes.

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