linux-kernel - Re: [PATCH] fsstack: fsstack_copy_inode

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Message-ID: <7439.1214831292@jrobl>
Date:	Mon, 30 Jun 2008 22:08:12 +0900
From:	hooanon05@...oo.co.jp
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Erez Zadok <ezk@...sunysb.edu>,
	Andrew Morton <akpm@...ux-foundation.org>, mhalcrow@...ibm.com,
	hch@...radead.org, viro@...iv.linux.org.uk,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fsstack: fsstack_copy_inode_size locking 


Hugh Dickins:
> It certainly shouldn't be.  The problem would have come from two
> racing i_size_write(dst)s, one of the unlocked increments getting
> lost, leaving seqcount odd, so the next i_size_read(dst) would
> spin forever waiting for it to go even.

I see.
The unlocked increment can cause the next i_size_read() hang.


> I'm not sure what you mean by that.  i_size_read() doesn't fail,
> but it may loop; and if the seqcount has got out of step from
> concurrent unlocked i_size_write()s, then it'll spin forever.

What I meant by "fail" was "loop" actually.
And I understand that you didn't writing directly (bypassing unionfs)
too.


Junjiro Okajima
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