linux-kernel - Re: [BUG BISECT] bug mm/vmalloc.c:470 (mm/vmalloc.c: get rid of one single unlink

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Date:   Tue, 4 Jun 2019 01:11:25 +1000
From:   Stephen Rothwell <sfr@...b.auug.org.au>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>, linux-kernel@...r.kernel.org,
        Hillf Danton <hdanton@...a.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tejun Heo <tj@...nel.org>, Andrei Vagin <avagin@...il.com>
Subject: Re: [BUG BISECT] bug mm/vmalloc.c:470 (mm/vmalloc.c: get rid of one
 single unlink_va() when merge)

Hi Krzysztof,

On Mon, 3 Jun 2019 16:35:22 +0200 Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On Mon, 3 Jun 2019 at 16:32, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
> >
> > On Mon, 3 Jun 2019 16:10:40 +0200 Krzysztof Kozlowski <krzk@...nel.org> wrote:  
> > >
> > > Indeed it looks like effect of merge conflict resolution or applying.
> > > When I look at MMOTS, it is the same as yours:
> > > http://git.cmpxchg.org/cgit.cgi/linux-mmots.git/commit/?id=b77b8cce67f246109f9d87417a32cd38f0398f2f
> > >
> > > However in linux-next it is different.
> > >
> > > Stephen, any thoughts?  
> >
> > Have you had a look at today's linux-next?  It looks correct in
> > there.  Andrew updated his patch series over the weekend.  
> 
> Yes, I am looking at today's next. Both the source code and the commit
> 728e0fbf263e3ed359c10cb13623390564102881 have wrong "if (merged)" (put
> in wrong hunk).

OK, I have replaced that commit with this:

From: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Subject: mm/vmalloc.c: get rid of one single unlink_va() when merge

It does not make sense to try to "unlink" the node that is definitely not
linked with a list nor tree.  On the first merge step VA just points to
the previously disconnected busy area.

On the second step, check if the node has been merged and do "unlink" if
so, because now it points to an object that must be linked.

Link: http://lkml.kernel.org/r/20190527151843.27416-4-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
Acked-by: Hillf Danton <hdanton@...a.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Joel Fernandes <joelaf@...gle.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Cc: Roman Gushchin <guro@...com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: Thomas Garnier <thgarnie@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 mm/vmalloc.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

--- a/mm/vmalloc.c~mm-vmap-get-rid-of-one-single-unlink_va-when-merge
+++ a/mm/vmalloc.c
@@ -719,9 +719,6 @@ merge_or_add_vmap_area(struct vmap_area
 			/* Check and update the tree if needed. */
 			augment_tree_propagate_from(sibling);
 
-			/* Remove this VA, it has been merged. */
-			unlink_va(va, root);
-
 			/* Free vmap_area object. */
 			kmem_cache_free(vmap_area_cachep, va);
 
@@ -746,12 +743,11 @@ merge_or_add_vmap_area(struct vmap_area
 			/* Check and update the tree if needed. */
 			augment_tree_propagate_from(sibling);
 
-			/* Remove this VA, it has been merged. */
-			unlink_va(va, root);
+			if (merged)
+				unlink_va(va, root);
 
 			/* Free vmap_area object. */
 			kmem_cache_free(vmap_area_cachep, va);
-
 			return;
 		}
 	}
_

Which is the patch from mmots but with different line numbers.
-- 
Cheers,
Stephen Rothwell

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