On Mon, May 03, 2010 at 09:53:44AM +0530, Nikanth Karthikesan wrote:
> On Saturday 01 May 2010 12:34:26 Amit K. Arora wrote:
> > On Fri, Apr 30, 2010 at 02:33:19PM -0700, Andrew Morton wrote:
> > > Also, there doesn't seem to be much point in doing
> > >
> > > mutex_lock(i_mutex);
> > > if (some_condition)
> > > bale out
> > > mutex_unlock(i_mutex);
> > >
> > > <stuff>
> > >
> > > because `some_condition' can now become true before or during the
> > > execution of `stuff'.
> > >
> > > IOW, it's racy.
>
> oh, yes. :(
>
> > Agreed. How about doing this check in the filesystem specific fallocate
> > inode routines instead ? For example, in ext4 we could do :
>
> I guess, calling the filesystem specific fallocate with the lock held would
> create lock ordering problems? If so, this might be the only way. But it would
> be better to document at the call site, that the callee should check for
> RLIMIT_FSIZE.
Hmm.. I never said to call the filesystem specific fallocate with
i_mutex held. What I suggested was that each filesystem at some point
anyhow takes the i_mutex to preallocate. Thats where the check should
be, to avoid the race. This is what the example patch below does.
--
Regards,
Amit Arora
> Thanks
> Nikanth
>
> > diff -Nuarp linux-2.6.org/fs/ext4/extents.c linux-2.6.new/fs/ext4/extents.c
> > --- linux-2.6.org/fs/ext4/extents.c 2010-05-01 12:16:07.000000000 +0530
> > +++ linux-2.6.new/fs/ext4/extents.c 2010-05-01 12:17:37.000000000 +0530
> > @@ -3672,6 +3672,11 @@ long ext4_fallocate(struct inode *inode,
> > */
> > credits = ext4_chunk_trans_blocks(inode, max_blocks);
> > mutex_lock(&inode->i_mutex);
> > + ret = inode_newsize_ok(inode, (offset + len));
> > + if (ret) {
> > + mutex_unlock(&inode->i_mutex);
> > + return ret;
> > + }
> > retry:
> > while (ret >= 0 && ret < max_blocks) {
> > block = block + ret;
> >
> >
> > Similarly for ocfs2, btrfs and xfs..
> >
> > --
> > Regards,
> > Amit Arora
> >
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