On Tue, Oct 18, 2005 at 07:26:46PM -0700, Andrew Morton wrote:
> > > 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:
The math ends up the same, but for your version there is a window where
the lock isn't held and the count doesn't reflect reality. I don't know
if anyone can race in and mess with the inode though. It is still on
various lists, but if we're only in that part of generic_forget_inode
during unmount, the super semaphore will keep out most potential racers.
I need to read harder.
> > 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.
>
It goes negative in the invalidate_inodes run during unmount. I
think Andrea's patch will solve that part, hopefully we'll know more
tomorrow.
-chris
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