RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c"

David Laight
2020-10-21T20:59:59Z

From: Greg KH
> Sent: 21 October 2020 17:13
>
> On Fri, Sep 25, 2020 at 06:51:39AM +0200, Christoph Hellwig wrote:
> > From: David Laight <David.Laight@ACULAB.COM>
> >
> > This lets the compiler inline it into import_iovec() generating
> > much better code.
> >
> > Signed-off-by: David Laight <david.laight@aculab.com>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> > fs/read_write.c | 179 ------------------------------------------------
> > lib/iov_iter.c | 176 +++++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 176 insertions(+), 179 deletions(-)
>
> Strangely, this commit causes a regression in Linus's tree right now.
>
> I can't really figure out what the regression is, only that this commit
> triggers a "large Android system binary" from working properly. There's
> no kernel log messages anywhere, and I don't have any way to strace the
> thing in the testing framework, so any hints that people can provide
> would be most appreciated.

My original commit just moved the function source from one file to another.
So it is odd that it makes any difference.
I don't even know if it gets inlined by Christoph's actual patch.
(I have another patch that depended on it that I need to resubmit.)

Some of the other changes from Christoph's same patch set might
make a difference though.

Might be worth forcing it to be not inlined - so it is no change.
Or try adding a kernel log to import_iovec() or the associated
copy failing.

David

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