linux-kernel - RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov

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Date:   Wed, 21 Oct 2020 20:59:43 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Greg KH' <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@....de>,
        "kernel-team@...roid.com" <kernel-team@...roid.com>
CC:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
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        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
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        "linux-aio@...ck.org" <linux-aio@...ck.org>,
        "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
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        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>
Subject: RE: Buggy commit tracked to: "Re: [PATCH 2/9] iov_iter: move
 rw_copy_check_uvector() into lib/iov_iter.c"

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@...LAB.COM>
> >
> > This lets the compiler inline it into import_iovec() generating
> > much better code.
> >
> > Signed-off-by: David Laight <david.laight@...lab.com>
> > Signed-off-by: Christoph Hellwig <hch@....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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