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.
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
