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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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