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SubjectRe: WARNING: at mm/page-writeback.c:1990 __set_page_dirty_nobuffers+0x13a/0x170()
On Fri, Jun 01, 2012 at 01:44:44AM -0700, Hugh Dickins wrote:

> > 3f31d07571eeea18a7d34db9af21d2285b807a17 is the first bad commit
> > commit 3f31d07571eeea18a7d34db9af21d2285b807a17
> > Author: Hugh Dickins <hughd@google.com>
> > Date: Tue May 29 15:06:40 2012 -0700
> >
> > mm/fs: route MADV_REMOVE to FALLOC_FL_PUNCH_HOLE
> >
> > Now tmpfs supports hole-punching via fallocate(), switch madvise_remove()
> > to use do_fallocate() instead of vmtruncate_range(): which extends
> > madvise(,,MADV_REMOVE) support from tmpfs to ext4, ocfs2 and xfs.
> >
> > Hugh ?
>
> Ow, you've caught me.

As I said in another mail, it looks like the bisect was wrong somewhere,
as with this backed out I still see problems.

> One half of the patch at the bottom should fix that: I'm not sure that
> it's the fix we actually want (a mapping_cap_account_dirty test might
> be more appropriate, but it's easier just to test a page flag here);
> but it should be good to shed more light on the problem.

I'll give the patch a try anyway, as builds are quick on that box.

> So I'm wondering if your trinity fuzzer happens to succeed a lot more
> often on madvise MADV_REMOVEs than fallocate FALLOC_FL_PUNCH_HOLEs, and
> the bug you converged on is not in tmpfs, but in ext4 (or xfs? or ocfs2?),
> which began to support MADV_REMOVE with that commit.

ext4 is a possibility.

> So the second half of the patch should show which filesystem's page is
> involved when you hit the WARN_ON - unless the first half of the patch
> turns out to stop the warnings completely, in which case I need to think
> harder about what was going on in tmpfs, and whether it matters.
>
> Or another possibility is that the bad commit doesn't actually touch mm
> at all: you were doing a bisection just on mm/ changes, weren't you?

oh, good point. It hadn't occured to me that this could be fs related.
The mm-heavy stack-trace may have misled me.

> > Sometimes during the bisect these errors happened
> > in pairs, sometimes only together.
>
> Sometimes in pairs, sometimes together? I don't understand.

beware late-night emails. I meant sometimes I saw both the list-debug's and the WARN,
but other times I saw only one or the other.

> Please give this patch a try (preferably on current git), and let us know.

Will do.

Dave


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