On Sat, 30 Nov 1996 15:44:33 -0500 (EST), Benjamin C R LaHaise
<blah@dot.superaje.com> said:
> On Fri, 29 Nov 1996, Stephen C. Tweedie wrote:
>> On investigation this appears to be the case --- FAT is ignoring a
>> totally undocumented requirement of the VFS. :) The reuse of inodes
>> can't happen as long as the put_inode() operation keeps the inode
>> in-use flag set right up until the end.
>> Does this much smaller patch fix your problem?
> The smaller (admittedly more beautiful) patch doesn't quite fix the
> problem. For example, in lofs I have the following sort of code in
> put_inode:
> static int lofs_put_inode(struct inode *inode)
> {
> struct inode *ino = inode->u.lofs_i.inode;
> lofs_check_inode(inode); /* debugging */
> clear_inode(inode);
> if (ino)
> iput(ino);
> return 1;
> }
> My problem is that clear_inode *must* be called before iput,
> otherwise another task might come along and reuse the
> inode.... splat! If it could have been done the other way, I would
> have.
That's an issue for the filesystem itself to address, not a deficiency
of the VFS. It is still essential that the filesystem does block
after dropping inode->i_count to zero. Fortunately, there is an easy
way around this: in your code above, just rewrite it as
lofs_check_inode(inode); /* debugging */
clear_inode(inode);
inode->i_count++;
if (ino)
iput(ino);
inode->i_count--;
before returning. That preserves the semantics that the VFS expects
while eliminating the race concerning inode reuse.
Cheers,
Stephen.
-- Stephen Tweedie <sct@dcs.ed.ac.uk> Department of Computer Science, Edinburgh University, Scotland.