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

[Al Viro <viro@ZenIV.linux.org.uk>]

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().