lkml.org 
[lkml]   [2006]   [Dec]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: 2.6.19 file content corruption on ext3
On Mon, 18 Dec 2006 18:22:42 +1100
Nick Piggin <nickpiggin@yahoo.com.au> wrote:

> Andrew Morton wrote:
> > On Mon, 18 Dec 2006 15:51:52 +1100
> > Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> >
> >
> >>I think the problem Andrew identified is real.
> >
> >
> > I don't. In fact I don't think I described any problem (well, I tried to,
> > but then I contradicted myself).
>
> By saying that there shouldn't be any dirty ptes if there are no
> dirty buffers? But in that case the _page_ shouldn't be dirty either,
> so that clear_page_dirty would be redundant. But presumably it isn't.

I don't follow that.

The linkage between pte-dirtiness and buffer_heads is a bit hard to follow
without also considering page-dirtiness.

> > Six hours here of fsx-linux plus high memory pressure on SMP on 1k
> > blocksize ext3, mainline. Zero failures. It's unlikely that this testing
> > would pass, yet people running normal workloads are able to easily trigger
> > failures. I suspect we're looking in the wrong place.
>
> Yes I could believe it the corruption is caused by something else
> completely.

Think so. We do have a problem here, but only on threaded apps, I believe.
rtorrent doesn't appear to be threaded, and the bug is hit on non-preempt
UP.

> >>The issue is the disconnect between the pte dirtiness and a filesystem
> >>bringing buffers clean.
> >
> >
> > Really? The dirtying direction goes pte_dirty->PG_dirty->BH_Dirty and the
> > cleaning direction goes !BH_Dirty->!PG_dirty->!pte_dirty. That's pretty
> > simple, setting aside races.
> >
> > In the try_to_free_buffers case there's a large time inverval between
> > !BH_Dirty and !PG_dirty, but that shouldn't affect anything.
>
> After try_to_free_buffers detaches the buffers from the page, a
> pagefault can come in, and mark the pte writeable, then set_page_dirty
> (which finds no buffers, so only sets PG_dirty).
>
> The page can now get dirtied through this mapping.
>
> try_to_free_buffers then goes on to clean the page and ptes.

try_to_free_buffers() isn't called against a page which doesn't have
buffers. It'll oops.

> Were you testing with preempt?

nope, just SMP.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-12-18 10:23    [W:0.185 / U:0.532 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site