linux-kernel - Re: [PATCH 1/3] IMA: move read/write counters into struct inode

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Message-ID: <20101020031504.GA18581@ZenIV.linux.org.uk>
Date:	Wed, 20 Oct 2010 04:15:04 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org, zohar@...ibm.com,
	warthog9@...nel.org, david@...morbit.com, jmorris@...ei.org,
	kyle@...artin.ca, hpa@...or.com, akpm@...ux-foundation.org,
	mingo@...e.hu
Subject: Re: [PATCH 1/3] IMA: move read/write counters into struct inode

On Tue, Oct 19, 2010 at 01:11:33PM -0600, Matthew Wilcox wrote:
> Hm.  Sounds like the same question that the file leases code needs
> answered.  The important difference is that the leases code can just
> refuse to set a lease on inodes with multiple dentries.
> 
> While my mind's on it ... Al, is this code even close to correct?
> 
>                 if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0))
>                         goto out;
>                 if ((arg == F_WRLCK)
>                     && ((atomic_read(&dentry->d_count) > 1)
>                         || (atomic_read(&inode->i_count) > 1)))
>                         goto out;

No.  This is complete junk; note that e.g. ls -lR will disrupt it, since
lstat(2) will bump dentry refcount.  The first part is more or less OK;
the second makes no sense.

What is it trying to do?  Note that the first part also doesn't make a lot
of sense, since you could be acquiring a write reference *right* *now*,
just as that check passes.  And you could finish getting it before you get
to do anything else in generic_setlease().
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