linux-kernel - Re: linux-next: Tree for Jan 7

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Message-ID: <20150107191813.GA28881@roeck-us.net>
Date:	Wed, 7 Jan 2015 11:18:13 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux-sh@...r.kernel.org
Subject: Re: linux-next: Tree for Jan 7

On Wed, Jan 07, 2015 at 10:09:22AM -0800, Paul E. McKenney wrote:
> On Wed, Jan 07, 2015 at 09:30:22AM -0800, Guenter Roeck wrote:
> > On Wed, Jan 07, 2015 at 08:33:10AM -0800, Paul E. McKenney wrote:
> > > On Wed, Jan 07, 2015 at 06:26:56AM -0800, Guenter Roeck wrote:
> > > > On Wed, Jan 07, 2015 at 03:16:18PM +1100, Stephen Rothwell wrote:
> > > > > Hi all,
> > > > > 
> > > > > Changes since 20150106:
> > > > > 
> > > > > *crickets*
> > > > > 
> > > > > Non-merge commits (relative to Linus' tree): 1350
> > > > >  1543 files changed, 41856 insertions(+), 24250 deletions(-)
> > > > > 
> > > > > ----------------------------------------------------------------------------
> > > > > 
> > > > 
> > > > New build failure for sh:dreamcast_defconfig:
> > > > 
> > > > arch/sh/mm/gup.c: In function 'gup_get_pte':
> > > > arch/sh/mm/gup.c:20:2: error: invalid initializer
> > > > make[1]: *** [arch/sh/mm/gup.o] Error 1
> > > > 
> > > > bisect log:
> > > > 
> > > > # bad: [7e3619a6de57f0257a2f6480182d2287ee05e314] Add linux-next specific files for 20150107
> > > > # good: [b1940cd21c0f4abdce101253e860feff547291b0] Linux 3.19-rc3
> > > > git bisect start 'HEAD' 'v3.19-rc3'
> > > > # good: [c48667c5659248ff2b2fbff5cd23c43b5768e81b] Merge remote-tracking branch 'net-next/master'
> > > > git bisect good c48667c5659248ff2b2fbff5cd23c43b5768e81b
> > > > # good: [b8cf629ce7d554711dd7ab256b00e6110355e1d7] Merge remote-tracking branch 'mmc-uh/next'
> > > > git bisect good b8cf629ce7d554711dd7ab256b00e6110355e1d7
> > > > # good: [cc52ff032bc2d91c78d7cf9aefcfa9e266ace816] Merge remote-tracking branch 'rcu/rcu/next'
> > > > git bisect good cc52ff032bc2d91c78d7cf9aefcfa9e266ace816
> > > > # bad: [9634277bcdab7b9d6a91409dc11d85502aa2e74b] Merge remote-tracking branch 'access_once/linux-next'
> > > > git bisect bad 9634277bcdab7b9d6a91409dc11d85502aa2e74b
> > > > # good: [261379560ee6aa65b4869c94eda0d3d60773aca3] Merge remote-tracking branch 'scsi/for-next'
> > > > git bisect good 261379560ee6aa65b4869c94eda0d3d60773aca3
> > > > # good: [38d45afa56bfca714780e45532760d64cd53b65b] Merge remote-tracking branch 'llvmlinux/for-next'
> > > > git bisect good 38d45afa56bfca714780e45532760d64cd53b65b
> > > > # good: [9afbe1ce2403c7d097bfaafcc5b27950040f7608] Merge remote-tracking branch 'y2038/y2038'
> > > > git bisect good 9afbe1ce2403c7d097bfaafcc5b27950040f7608
> > > > # bad: [a91ed664749cbec0325ef9da7d12619d9bb72e2d] kernel: tighten rules for ACCESS ONCE
> > > > git bisect bad a91ed664749cbec0325ef9da7d12619d9bb72e2d
> > > > # good: [e3865cc4a17e979e6b2f26af026686fae5567096] x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE
> > > > git bisect good e3865cc4a17e979e6b2f26af026686fae5567096
> > > > # good: [e2579c6f22ee0a43394d603cef6989dca98c5610] mm/gup: Replace ACCESS_ONCE with READ_ONCE
> > > > git bisect good e2579c6f22ee0a43394d603cef6989dca98c5610
> > > > # first bad commit: [a91ed664749cbec0325ef9da7d12619d9bb72e2d] kernel: tighten rules for ACCESS ONCE
> > > > 
> > > > Maybe the ACCESS_ONCE in the affected file should be replaced with READ_ONCE ?
> > > 
> > > That is my belief.  What happens when you try it?
> > > 
> > Build passes, and my qemu tests pass as well. That doesn't mean
> > that the change is correct, of course, since I don't know if the code
> > in question is executed.
> 
> Would it be possible to increment a counter at that location, then
> print it out at some convenient point?
> 
I made it simpler and just added a call to panic() ... which had no effect,
so the function is not called in my qemu tests. Any idea what I would have
to do to trigger a call ?

> > Should I send a patch with the change ?
> 
> I believe such a patch is needed.  Testing would be good, but the patch
> is what we were thinking of for this situation.
> 
I'll probably send a patch marked "compile-tested only" if I can't find a way
to test the change.

Guenter
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