Chris Mason <[email protected]> wrote:
>
> On Tue, Oct 18, 2005 at 06:15:48PM -0700, Andrew Morton wrote:
> > > > Well according to my assertion (below), the inode in __sync_single_inode()
> > > > cannot have a zero refcount, so the whole if() statement is never executed.
> > >
> > > generic_forget_inode->write_inode_now->__writeback_single_inode->
> > > __sync_single_inode
> >
> > oshit.
>
> When does this ever happen? Just for private inodes released during
> put_super right?
I suppose so, yes.
> >
> > > We do have I_WILL_FREE, but i_count will be zero.
> >
> > yup.
> >
> > > >
> > > > The thinking behind that increment is that __sync_single_inode() has just
> > > > taken a dirty, zero-refcount inode and has cleaned it. A dirty inode
> > > > cannot have previously been on inode_unused, hence we now are newly moving
> > > > it to inode_unused.
> > >
> > > nr_unused doesn't seem to count the number of inodes on the unused list.
> > > It is actually counting the number of inodes whose i_count is 0. See
> > > generic_forget_inode and invalidate_list to see what I mean.
> >
> > hm, OK. It'd be nice to make that more explicit. Something like this?
>
> Well, I can't quite convince myself it is wrong, but when
> (!sb || (sb->s_flags & MS_ACTIVE), we're dropping the
> inode_lock with an inode with i_count == 0 and nr_unused hasn't been
> incremented.
>
> So, if someone (sync_sb_inodes?) comes in and runs __iget,
> the counts end up wrong. Then again, whoever ran __iget would also run
> iput and things would go horribly wrong anyway.
Nope, it's equivalent:
--- devel/fs/inode.c~generic_forget_inode-nr_unused-cleanup 2005-10-18 18:13:22.000000000 -0700
+++ devel-akpm/fs/inode.c 2005-10-18 18:13:57.000000000 -0700
@@ -1067,8 +1067,8 @@ static void generic_forget_inode(struct
if (!hlist_unhashed(&inode->i_hash)) {
if (!(inode->i_state & (I_DIRTY|I_LOCK)))
list_move(&inode->i_list, &inode_unused);
- inodes_stat.nr_unused++;
if (!sb || (sb->s_flags & MS_ACTIVE)) {
+ inodes_stat.nr_unused++; /* One more 0-ref inode */
spin_unlock(&inode_lock);
return;
}
@@ -1077,7 +1077,6 @@ static void generic_forget_inode(struct
write_inode_now(inode, 1);
spin_lock(&inode_lock);
inode->i_state &= ~I_WILL_FREE;
- inodes_stat.nr_unused--;
hlist_del_init(&inode->i_hash);
}
list_del_init(&inode->i_list);
_
> Did I mention the part where Andrea and I are hunting a bug where the
> count of unused inodes goes negative and the everyone ends up spinning
> in shrink_icache_memory?
No.
> Andrea's patch doesn't fix the spinning, but
> it might have fixed the unused inode count going negative. We're
> waiting for another reproduce on the ppc64 race monster.
I assume you have BUG_ON(inode_stat.nr_unused < 0)s in there everywhere?
In fact WARN_ON(inode_stat.nr_unused < 100) might be better - something's
obviously doing a bogus decrement a lot of times.
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