Re: [PATCH] fix nr_unused accounting, and avoid recursing in iput with I_WILL_FREE set

[Chris Mason]

On Tue, Oct 18, 2005 at 07:26:46PM -0700, Andrew Morton wrote:
> Chris Mason <mason@xxxxxxxx> 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.

It's not related to the bug, but prune_icache can jump in at any
time during generic_shutdown_super, except during the invalidate_inodes
runs.  Something like this:

proc1				proc2
generic_shutdown_super
s->s_flags &= ~MS_ACTIVE
invalidate_inodes
put_super
				shrink_icache_memory
				prune_icache
				invalidate_inode_pages
				try_to_release_page
				
I doubt any FS triggers this.  They would need to generate inodes
with pages during the put_super call, and get them onto the unused list.
But, I think prune_icache should just skip any inodes where the super
doesn't have MS_ACTIVE set.

At any rate, this wasn't the race I was looking for.  Aside from the
bugs fixed by Andrea's patch, we were seeing inodes go negative thanks
to a bad interaction between a latency fix and a backport of something
else from mainline.   Our latency code has a goto again, and mainline
has a big fat comment explaining why goto again isn't needed.  

If the super->s_inodes list was long enough to reschedule in invalidate_list,
we would process the same inodes in multiple times without removing them.

The short version is that no additional patches should be needed for
mainline.

-chris

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