+ mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch added to mm-hotfixes-unstable branch

+ mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: page_alloc: free pages to correct buddy list after PCP lock contention
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Mel Gorman <mgorman@techsingularity.net>
Subject: mm: page_alloc: free pages to correct buddy list after PCP lock contention
Date: Tue, 5 Sep 2023 10:09:22 +0100

Commit 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock")
returns pages to the buddy list on PCP lock contention. However, for
migratetypes that are not MIGRATE_PCPTYPES, the migratetype may have
been clobbered already for pages that are not being isolated. In
practice, this means that CMA pages may be returned to the wrong
buddy list. While this might be harmless in some cases as it is
MIGRATE_MOVABLE, the pageblock could be reassigned in rmqueue_fallback
and prevent a future CMA allocation. Lookup the PCP migratetype
against unconditionally if the PCP lock is contended.

[lecopzer.chen@mediatek.com: CMA-specific fix]
Link: https://lkml.kernel.org/r/20230905090922.zy7srh33rg5c3zao@techsingularity.net
Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock")
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reported-by: Joe Liu <joe.liu@mediatek.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/mm/page_alloc.c~mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention
+++ a/mm/page_alloc.c
@@ -2428,7 +2428,13 @@ void free_unref_page(struct page *page,
 		free_unref_page_commit(zone, pcp, page, migratetype, order);
 		pcp_spin_unlock(pcp);
 	} else {
-		free_one_page(zone, page, pfn, order, migratetype, FPI_NONE);
+		/*
+		 * The page migratetype may have been clobbered for types
+		 * (type >= MIGRATE_PCPTYPES && !is_migrate_isolate) so
+		 * must be rechecked.
+		 */
+		free_one_page(zone, page, pfn, order,
+			      get_pcppage_migratetype(page), FPI_NONE);
 	}
 	pcp_trylock_finish(UP_flags);
 }
_

Patches currently in -mm which might be from mgorman@techsingularity.net are

mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch

Re: + mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch added to mm-hotfixes-unstable branch

[Johannes Weiner]

On Mon, Sep 11, 2023 at 02:00:52PM -0700, Andrew Morton wrote:
> 
> The patch titled
>      Subject: mm: page_alloc: free pages to correct buddy list after PCP lock contention
> has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
>      mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch
> 
> This patch will shortly appear at
>      https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch
> 
> This patch will later appear in the mm-hotfixes-unstable branch at
>     git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> 
> The -mm tree is included into linux-next via the mm-everything
> branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> and is updated there every 2-3 working days
> 
> ------------------------------------------------------
> From: Mel Gorman <mgorman@techsingularity.net>
> Subject: mm: page_alloc: free pages to correct buddy list after PCP lock contention
> Date: Tue, 5 Sep 2023 10:09:22 +0100
> 
> Commit 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock")
> returns pages to the buddy list on PCP lock contention. However, for
> migratetypes that are not MIGRATE_PCPTYPES, the migratetype may have
> been clobbered already for pages that are not being isolated. In
> practice, this means that CMA pages may be returned to the wrong
> buddy list. While this might be harmless in some cases as it is
> MIGRATE_MOVABLE, the pageblock could be reassigned in rmqueue_fallback
> and prevent a future CMA allocation. Lookup the PCP migratetype
> against unconditionally if the PCP lock is contended.
> 
> [lecopzer.chen@mediatek.com: CMA-specific fix]
> Link: https://lkml.kernel.org/r/20230905090922.zy7srh33rg5c3zao@techsingularity.net
> Fixes: 4b23a68f9536 ("mm/page_alloc: protect PCP lists with a spinlock")
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Reported-by: Joe Liu <joe.liu@mediatek.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

This patch is superseded by the following patch you picked up:
mm-page_alloc-fix-cma-and-highatomic-landing-on-the-wrong-buddy-list.patch

If you drop this patch here, you can also drop the fixlet to
free_unref_page(). The branch in there should look like this:

	if (pcp)
		free_unref_page_commit(..., pcpmigratetype, ...);
	else
		free_one_page(..., migratetype, ...);

Re: + mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

On Tue, 12 Sep 2023 09:50:29 -0400 Johannes Weiner <hannes@cmpxchg.org> wrote:

> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> 
> This patch is superseded by the following patch you picked up:
> mm-page_alloc-fix-cma-and-highatomic-landing-on-the-wrong-buddy-list.patch

OK.

> If you drop this patch here, you can also drop the fixlet to
> free_unref_page(). The branch in there should look like this:
> 
> 	if (pcp)
> 		free_unref_page_commit(..., pcpmigratetype, ...);
> 	else
> 		free_one_page(..., migratetype, ...);

Well kinda.  It's actually

	if (pcp) {
		free_unref_page_commit(zone, pcp, page, migratetype, order);
		pcp_spin_unlock(pcp);
	} else {
		free_one_page(zone, page, pfn, order, migratetype, FPI_NONE);
	}

Re: + mm-page_alloc-free-pages-to-correct-buddy-list-after-pcp-lock-contention.patch added to mm-hotfixes-unstable branch

[Johannes Weiner]

On Tue, Sep 12, 2023 at 09:09:38AM -0700, Andrew Morton wrote:
> On Tue, 12 Sep 2023 09:50:29 -0400 Johannes Weiner <hannes@cmpxchg.org> wrote:
> 
> > > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > > Cc: <stable@vger.kernel.org>
> > > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > 
> > This patch is superseded by the following patch you picked up:
> > mm-page_alloc-fix-cma-and-highatomic-landing-on-the-wrong-buddy-list.patch
> 
> OK.
> 
> > If you drop this patch here, you can also drop the fixlet to
> > free_unref_page(). The branch in there should look like this:
> > 
> > 	if (pcp)
> > 		free_unref_page_commit(..., pcpmigratetype, ...);
> > 	else
> > 		free_one_page(..., migratetype, ...);
> 
> Well kinda.  It's actually
> 
> 	if (pcp) {
> 		free_unref_page_commit(zone, pcp, page, migratetype, order);

							^^ pcpmigratetype

is what I was trying to highlight.

But yes, the pcp_spin_unlock() is needed too!

> 		pcp_spin_unlock(pcp);
> 	} else {
> 		free_one_page(zone, page, pfn, order, migratetype, FPI_NONE);
> 	}
>