linux-kernel - Re: [PATCH 1/3] Revert "dax: fix NULL pointer in __dax_pmd

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Date:	Mon, 5 Oct 2015 10:49:06 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <dchinner@...hat.com>, Jan Kara <jack@...e.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH 1/3] Revert "dax: fix NULL pointer in __dax_pmd_fault()"

On Fri 02-10-15 17:28:42, Ross Zwisler wrote:
> On Fri, Oct 02, 2015 at 02:11:03PM -0700, Dan Williams wrote:
> > On Fri, Oct 2, 2015 at 2:02 PM, Ross Zwisler
> > <ross.zwisler@...ux.intel.com> wrote:
> > > This reverts commit 8346c416d17bf5b4ea1508662959bb62e73fd6a5.
> > >
> > > This commit did fix the issue it intended to fix, but it turns out that
> > > the locking changes introduced by these two commits:
> > >
> > > commit 843172978bb9 ("dax: fix race between simultaneous faults")
> > > commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for DAX")
> > >
> > > had other issues as well, so they need to just be reverted.
> > 
> > Wait, why introduce two points in the kernel history where we have a
> > known uninitialized variable?  I'd say fix up the revert of "mm: take
> > i_mmap_lock in unmap_mapping_range() for DAX" to address the conflict
> > with the fix, one less patch and keeps the stability rolling forward.
> 
> Essentially because I wasn't sure about the rules regarding reverts, if there
> are any.  I assumed (perhaps incorrectly) that you'd want a 1:1 relationship
> between original commits and reverts.  If it's better to not have intermediate
> breakage, sure, let's squash them.

Well, reverts aren't any special commits after all. So if it is simple
enough to just revert part of the patch that is broken, then just reverting
that part is fine.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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