On Wed, 2019-04-03 at 11:55 +1100, NeilBrown wrote:
> On Wed, Apr 03 2019, Ian Kent wrote:
>
> > On Tue, 2019-04-02 at 20:08 +0100, Al Viro wrote:
> > > On Tue, Apr 02, 2019 at 06:54:01PM +0100, Al Viro wrote:
> > > > static void autofs_dentry_release(struct dentry *de)
> > > > {
> > > > struct autofs_info *ino = autofs_dentry_ino(de);
> > > > struct autofs_sb_info *sbi = autofs_sbi(de->d_sb);
> > > >
> > > > pr_debug("releasing %p\n", de);
> > > >
> > > > if (!ino)
> > > > return;
> > > > ...
> > > > autofs_free_ino(ino);
> > > > }
> > > > with autofs_free_ino() being straight kfree(). Which means
> > > > that the lockless case of autofs_d_manage() can run into
> > > > autofs_dentry_ino(dentry) getting freed right under it.
> > > >
> > > > And there we do have this reachable:
> > > > int autofs_expire_wait(const struct path *path, int rcu_walk)
> > > > {
> > > > struct dentry *dentry = path->dentry;
> > > > struct autofs_sb_info *sbi = autofs_sbi(dentry->d_sb);
> > > > struct autofs_info *ino = autofs_dentry_ino(dentry);
> > > > int status;
> > > > int state;
> > > >
> > > > /* Block on any pending expire */
> > > > if (!(ino->flags & AUTOFS_INF_WANT_EXPIRE))
> >
> > Oh yes, this is saying the dentry hasn't been selected
> > for expire on the first pass, there's a second pass at
> > expire selection so there's a delay there and both flags
> > (this one and the expiring flag) are kept throughout the
> > expire operation if dentry is selected.
> >
> > That might be partly why an oops has never been seen but
> > path walks can occur at any time so it's a bit puzzling.
> >
> > LOL, and Neil probably can't remember the deeper detail
> > on what he did there now either.
>
> It seems very likely that this was just a subtlety that I missed.
> I doesn't help that "ino" isn't actually and inode and isn't freed like
> an inode, but that is no excuse.
I've become accustom to the naming so that doesn't occur to
me, ;)
>
> When we add the rcu_head linkage to 'struct autofs_info', we might as
> well remove the 'struct inode' from there - it doesn't seem to have been
> used for years.
That's a good point, I've thought about doing so several
times but haven't got around to it.
Ian
