Re: [PATCH AUTOSEL 4.20 66/72] mm, memory_hotplug: is_mem_section_removable do not pass the end of a zone

[Mike Rapoport]

On Sat, Feb 23, 2019 at 04:04:16PM -0500, Sasha Levin wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
> 
> [ Upstream commit efad4e475c312456edb3c789d0996d12ed744c13 ]
 
There is a fix for this fix [1].

It's  commit 891cb2a72d821f930a39d5900cb7a3aa752c1d5b ("mm, memory_hotplug:
fix off-by-one in is_pageblock_removable") in mainline.
    
[1] https://lore.kernel.org/lkml/20190218181544.14616-1-mhocko@xxxxxxxxxx/


> Patch series "mm, memory_hotplug: fix uninitialized pages fallouts", v2.
> 
> Mikhail Zaslonko has posted fixes for the two bugs quite some time ago
> [1].  I have pushed back on those fixes because I believed that it is
> much better to plug the problem at the initialization time rather than
> play whack-a-mole all over the hotplug code and find all the places
> which expect the full memory section to be initialized.
> 
> We have ended up with commit 2830bf6f05fb ("mm, memory_hotplug:
> initialize struct pages for the full memory section") merged and cause a
> regression [2][3].  The reason is that there might be memory layouts
> when two NUMA nodes share the same memory section so the merged fix is
> simply incorrect.
> 
> In order to plug this hole we really have to be zone range aware in
> those handlers.  I have split up the original patch into two.  One is
> unchanged (patch 2) and I took a different approach for `removable'
> crash.
> 
> [1] http://lkml.kernel.org/r/20181105150401.97287-2-zaslonko@xxxxxxxxxxxxx
> [2] https://bugzilla.redhat.com/show_bug.cgi?id=1666948
> [3] http://lkml.kernel.org/r/20190125163938.GA20411@xxxxxxxxxxxxxx
> 
> This patch (of 2):
> 
> Mikhail has reported the following VM_BUG_ON triggered when reading sysfs
> removable state of a memory block:
> 
>  page:000003d08300c000 is uninitialized and poisoned
>  page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>  Call Trace:
>    is_mem_section_removable+0xb4/0x190
>    show_mem_removable+0x9a/0xd8
>    dev_attr_show+0x34/0x70
>    sysfs_kf_seq_show+0xc8/0x148
>    seq_read+0x204/0x480
>    __vfs_read+0x32/0x178
>    vfs_read+0x82/0x138
>    ksys_read+0x5a/0xb0
>    system_call+0xdc/0x2d8
>  Last Breaking-Event-Address:
>    is_mem_section_removable+0xb4/0x190
>  Kernel panic - not syncing: Fatal exception: panic_on_oops
> 
> The reason is that the memory block spans the zone boundary and we are
> stumbling over an unitialized struct page.  Fix this by enforcing zone
> range in is_mem_section_removable so that we never run away from a zone.
> 
> Link: http://lkml.kernel.org/r/20190128144506.15603-2-mhocko@xxxxxxxxxx
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> Reported-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>
> Debugged-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>
> Tested-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@xxxxxxxxx>
> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  mm/memory_hotplug.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 21d94b5677e81..5ce0d929ff482 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1234,7 +1234,8 @@ static bool is_pageblock_removable_nolock(struct page *page)
>  bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
>  {
>  	struct page *page = pfn_to_page(start_pfn);
> -	struct page *end_page = page + nr_pages;
> +	unsigned long end_pfn = min(start_pfn + nr_pages, zone_end_pfn(page_zone(page)));
> +	struct page *end_page = pfn_to_page(end_pfn);
> 
>  	/* Check the starting page of each pageblock within the range */
>  	for (; page < end_page; page = next_active_pageblock(page)) {
> -- 
> 2.19.1
> 

-- 
Sincerely yours,
Mike.