FAILED: patch "[PATCH] mm: add VM_BUG_ON_PAGE() to page_mapcount()" failed to apply to 4.4-stable tree

FAILED: patch "[PATCH] mm: add VM_BUG_ON_PAGE() to page_mapcount()" failed to apply to 4.4-stable tree

[gregkh]

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1d148e218a0d0566b1c06f2f45f1436d53b049b2 Mon Sep 17 00:00:00 2001
From: "Wang, Yalin" <Yalin.Wang@sonymobile.com>
Date: Wed, 11 Feb 2015 15:24:48 -0800
Subject: [PATCH] mm: add VM_BUG_ON_PAGE() to page_mapcount()

Add VM_BUG_ON_PAGE() for slab pages.  _mapcount is an union with slab
struct in struct page, so we must avoid accessing _mapcount if this page
is a slab page.  Also remove the unneeded bracket.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8dd4fde9d2e5..c6bf813a6b3d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -484,7 +484,8 @@ static inline void page_mapcount_reset(struct page *page)
 
 static inline int page_mapcount(struct page *page)
 {
-	return atomic_read(&(page)->_mapcount) + 1;
+	VM_BUG_ON_PAGE(PageSlab(page), page);
+	return atomic_read(&page->_mapcount) + 1;
 }
 
 static inline int page_count(struct page *page)

Re: FAILED: patch "[PATCH] mm: add VM_BUG_ON_PAGE() to page_mapcount()" failed to apply to 4.4-stable tree

[Kirill A. Shutemov]

On Mon, Jun 01, 2020 at 01:07:24PM +0200, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 4.4-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.

Please don't.

The patch known to cause trouble and going to be effectively reverted:

https://lore.kernel.org/r/159032779896.957378.7852761411265662220.stgit@buzz

If you have it in any other stable queue, please drop it.

> ------------------ original commit in Linus's tree ------------------
> 
> From 1d148e218a0d0566b1c06f2f45f1436d53b049b2 Mon Sep 17 00:00:00 2001
> From: "Wang, Yalin" <Yalin.Wang@sonymobile.com>
> Date: Wed, 11 Feb 2015 15:24:48 -0800
> Subject: [PATCH] mm: add VM_BUG_ON_PAGE() to page_mapcount()
> 
> Add VM_BUG_ON_PAGE() for slab pages.  _mapcount is an union with slab
> struct in struct page, so we must avoid accessing _mapcount if this page
> is a slab page.  Also remove the unneeded bracket.
> 
> Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8dd4fde9d2e5..c6bf813a6b3d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -484,7 +484,8 @@ static inline void page_mapcount_reset(struct page *page)
>  
>  static inline int page_mapcount(struct page *page)
>  {
> -	return atomic_read(&(page)->_mapcount) + 1;
> +	VM_BUG_ON_PAGE(PageSlab(page), page);
> +	return atomic_read(&page->_mapcount) + 1;
>  }
>  
>  static inline int page_count(struct page *page)
> 

-- 
 Kirill A. Shutemov

Re: FAILED: patch "[PATCH] mm: add VM_BUG_ON_PAGE() to page_mapcount()" failed to apply to 4.4-stable tree

[Greg KH]

On Mon, Jun 01, 2020 at 05:05:19PM +0300, Kirill A. Shutemov wrote:
> On Mon, Jun 01, 2020 at 01:07:24PM +0200, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 4.4-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> 
> Please don't.
> 
> The patch known to cause trouble and going to be effectively reverted:
> 
> https://lore.kernel.org/r/159032779896.957378.7852761411265662220.stgit@buzz

Oops, I ment to say that 6988f31d558a ("mm: remove VM_BUG_ON(PageSlab())
from page_mapcount()") did not apply to the 4.4 tree and needs a working
backport.

I put in the wrong id as that is the commit that 6988f31d558a fixes.

So, if you could provide a working backport, that would be wonderful.

thanks,

greg k-h

Re: FAILED: patch "[PATCH] mm: add VM_BUG_ON_PAGE() to page_mapcount()" failed to apply to 4.4-stable tree

[Kirill A. Shutemov]

On Mon, Jun 01, 2020 at 04:15:22PM +0200, Greg KH wrote:
> On Mon, Jun 01, 2020 at 05:05:19PM +0300, Kirill A. Shutemov wrote:
> > On Mon, Jun 01, 2020 at 01:07:24PM +0200, gregkh@linuxfoundation.org wrote:
> > > 
> > > The patch below does not apply to the 4.4-stable tree.
> > > If someone wants it applied there, or to any other stable or longterm
> > > tree, then please email the backport, including the original git commit
> > > id to <stable@vger.kernel.org>.
> > 
> > Please don't.
> > 
> > The patch known to cause trouble and going to be effectively reverted:
> > 
> > https://lore.kernel.org/r/159032779896.957378.7852761411265662220.stgit@buzz
> 
> Oops, I ment to say that 6988f31d558a ("mm: remove VM_BUG_ON(PageSlab())
> from page_mapcount()") did not apply to the 4.4 tree and needs a working
> backport.
> 
> I put in the wrong id as that is the commit that 6988f31d558a fixes.
> 
> So, if you could provide a working backport, that would be wonderful.

The patch below should do. I've dropped the comments. They are not
relevant for v4.4.

From e0568884b6bab1658d4e97d38b22b25c2e6eddeb Mon Sep 17 00:00:00 2001
From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Date: Wed, 27 May 2020 22:20:47 -0700
Subject: [PATCH] mm: remove VM_BUG_ON(PageSlab()) from page_mapcount()

Replace superfluous VM_BUG_ON() with comment about correct usage.

Technically reverts commit 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to
page_mapcount()"), but context lines have changed.

Function isolate_migratepages_block() runs some checks out of lru_lock
when choose pages for migration.  After checking PageLRU() it checks
extra page references by comparing page_count() and page_mapcount().
Between these two checks page could be removed from lru, freed and taken
by slab.

As a result this race triggers VM_BUG_ON(PageSlab()) in page_mapcount().
Race window is tiny.  For certain workload this happens around once a
year.

    page:ffffea0105ca9380 count:1 mapcount:0 mapping:ffff88ff7712c180 index:0x0 compound_mapcount: 0
    flags: 0x500000000008100(slab|head)
    raw: 0500000000008100 dead000000000100 dead000000000200 ffff88ff7712c180
    raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000
    page dumped because: VM_BUG_ON_PAGE(PageSlab(page))
    ------------[ cut here ]------------
    kernel BUG at ./include/linux/mm.h:628!
    invalid opcode: 0000 [#1] SMP NOPTI
    CPU: 77 PID: 504 Comm: kcompactd1 Tainted: G        W         4.19.109-27 #1
    Hardware name: Yandex T175-N41-Y3N/MY81-EX0-Y3N, BIOS R05 06/20/2019
    RIP: 0010:isolate_migratepages_block+0x986/0x9b0

The code in isolate_migratepages_block() was added in commit
119d6d59dcc0 ("mm, compaction: avoid isolating pinned pages") before
adding VM_BUG_ON into page_mapcount().

This race has been predicted in 2015 by Vlastimil Babka (see link
below).

[akpm@linux-foundation.org: comment tweaks, per Hugh]
Fixes: 1d148e218a0d ("mm: add VM_BUG_ON_PAGE() to page_mapcount()")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/159032779896.957378.7852761411265662220.stgit@buzz
Link: https://lore.kernel.org/lkml/557710E1.6060103@suse.cz/
Link: https://lore.kernel.org/linux-mm/158937872515.474360.5066096871639561424.stgit@buzz/T/ (v1)
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 include/linux/mm.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 69fa3df9e712..03cf5526e445 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -446,7 +446,6 @@ static inline void page_mapcount_reset(struct page *page)
 
 static inline int page_mapcount(struct page *page)
 {
-	VM_BUG_ON_PAGE(PageSlab(page), page);
 	return atomic_read(&page->_mapcount) + 1;
 }
 
-- 
 Kirill A. Shutemov

Re: FAILED: patch "[PATCH] mm: add VM_BUG_ON_PAGE() to page_mapcount()" failed to apply to 4.4-stable tree

[Greg KH]

On Mon, Jun 01, 2020 at 05:30:23PM +0300, Kirill A. Shutemov wrote:
> On Mon, Jun 01, 2020 at 04:15:22PM +0200, Greg KH wrote:
> > On Mon, Jun 01, 2020 at 05:05:19PM +0300, Kirill A. Shutemov wrote:
> > > On Mon, Jun 01, 2020 at 01:07:24PM +0200, gregkh@linuxfoundation.org wrote:
> > > > 
> > > > The patch below does not apply to the 4.4-stable tree.
> > > > If someone wants it applied there, or to any other stable or longterm
> > > > tree, then please email the backport, including the original git commit
> > > > id to <stable@vger.kernel.org>.
> > > 
> > > Please don't.
> > > 
> > > The patch known to cause trouble and going to be effectively reverted:
> > > 
> > > https://lore.kernel.org/r/159032779896.957378.7852761411265662220.stgit@buzz
> > 
> > Oops, I ment to say that 6988f31d558a ("mm: remove VM_BUG_ON(PageSlab())
> > from page_mapcount()") did not apply to the 4.4 tree and needs a working
> > backport.
> > 
> > I put in the wrong id as that is the commit that 6988f31d558a fixes.
> > 
> > So, if you could provide a working backport, that would be wonderful.
> 
> The patch below should do. I've dropped the comments. They are not
> relevant for v4.4.

That worked, thanks!

greg k-h