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    SubjectRe: [PATCH 0/4] IMA: making i_readcount a first class inode citizen
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    On Thu, 2010-11-04 at 21:12 -0400, J. Bruce Fields wrote:
    > On Thu, Oct 28, 2010 at 06:02:01PM -0400, Mimi Zohar wrote:
    > > On Mon, 2010-10-25 at 14:41 -0400, Eric Paris wrote:
    > >
    > > <snip>
    > >
    > > > I believe that IBM is going to look into making i_readcount a first
    > > > class citizen which can be used by both IMA and generic_setlease().
    > > > Then people could say IMA had 0 per inode overhead :)
    > >
    > > This patchset separates the incrementing/decrementing of the i_readcount,
    > > in the VFS layer, from other IMA functionality, by replacing the current
    > > ima_counts_get() call with iget_readcount(). Its unclear whether this
    > > call to increment i_readcount should be made earlier.
    > >
    > > The patch ordering is a bit redundant in order to leave removing the ifdef
    > > around i_readcount until the last patch. The first three patches: defines
    > > iget/iput_readcount(), moves the IMA functionality in ima_counts_get() to
    > > ima_file_check(), and removes the IMA imbalance code, simplifying IMA. The
    > > last patch moves iget/iput_readcount() to the fs directory and removes the
    > > ifdef around i_readcount, making i_readcount into a "first class inode citizen".
    > >
    > > The generic_setlease code could then take advantage of i_readcount, assuming
    > > it can take the spin_lock, by doing something like:
    > >
    > > - if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0))
    > > +
    > > + spin_lock(&inode->i_lock);
    > > + if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0)){
    > > + spin_unlock(&inode->i_lock);
    > > goto out;
    > > - if ((arg == F_WRLCK)
    > > - && ((atomic_read(&dentry->d_count) > 1)
    > > - || (atomic_read(&inode->i_count) > 1)))
    > > + }
    > > + if ((arg == F_WRLCK) && (inode->i_readcount > 1)) {
    > > + spin_unlock(&inode->i_lock);
    > > goto out;
    > > + }
    > > + spin_unlock(&inode->i_lock);
    > > }
    >
    > Seems like an improvement.
    >
    > It still leaves the race:
    >
    > may_open calls lease_break, finds no lease
    >
    > setlease checks read/writecount, finds 0,
    > creates lease
    >
    > __dentry_open bumps read/writecount
    >
    > (Is there any reason we couldn't move the break_lease to after bumping
    > read or write count?)
    >
    > --b.

    Right, like the ima_file_check(), which is after the __dentry_open().
    Al, is it possible to move the break_lease() in may_open() to later?

    thanks,

    Mimi



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