linux-kernel - Re: [PATCH AUTOSEL 4.14 62/95] mm, memory_hotplug: initialize struct pages for the full memory section

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Date:   Tue, 7 May 2019 09:31:10 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        Mikhail Zaslonko <zaslonko@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Michal Hocko <mhocko@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Pasha Tatashin <Pavel.Tatashin@...rosoft.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...rosoft.com>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH AUTOSEL 4.14 62/95] mm, memory_hotplug: initialize struct
 pages for the full memory section

On Mon, May 6, 2019 at 10:40 PM Sasha Levin <sashal@...nel.org> wrote:
>
> From: Mikhail Zaslonko <zaslonko@...ux.ibm.com>
>
> [ Upstream commit 2830bf6f05fb3e05bc4743274b806c821807a684 ]
>
> If memory end is not aligned with the sparse memory section boundary,
> the mapping of such a section is only partly initialized.  This may lead
> to VM_BUG_ON due to uninitialized struct page access from
> is_mem_section_removable() or test_pages_in_a_zone() function triggered
> by memory_hotplug sysfs handlers:
>
> Here are the the panic examples:
>  CONFIG_DEBUG_VM=y
>  CONFIG_DEBUG_VM_PGFLAGS=y
>
>  kernel parameter mem=2050M
>  --------------------------
>  page:000003d082008000 is uninitialized and poisoned
>  page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>  Call Trace:
>  ( test_pages_in_a_zone+0xde/0x160)
>    show_valid_zones+0x5c/0x190
>    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:
>    test_pages_in_a_zone+0xde/0x160
>  Kernel panic - not syncing: Fatal exception: panic_on_oops
>
>  kernel parameter mem=3075M
>  --------------------------
>  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
>
> Fix the problem by initializing the last memory section of each zone in
> memmap_init_zone() till the very end, even if it goes beyond the zone end.
>
> Michal said:
>
> : This has alwways been problem AFAIU.  It just went unnoticed because we
> : have zeroed memmaps during allocation before f7f99100d8d9 ("mm: stop
> : zeroing memory during allocation in vmemmap") and so the above test
> : would simply skip these ranges as belonging to zone 0 or provided a
> : garbage.
> :
> : So I guess we do care for post f7f99100d8d9 kernels mostly and
> : therefore Fixes: f7f99100d8d9 ("mm: stop zeroing memory during
> : allocation in vmemmap")
>
> Link: http://lkml.kernel.org/r/20181212172712.34019-2-zaslonko@linux.ibm.com
> Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")
> Signed-off-by: Mikhail Zaslonko <zaslonko@...ux.ibm.com>
> Reviewed-by: Gerald Schaefer <gerald.schaefer@...ibm.com>
> Suggested-by: Michal Hocko <mhocko@...nel.org>
> Acked-by: Michal Hocko <mhocko@...e.com>
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> Cc: Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Cc: Heiko Carstens <heiko.carstens@...ibm.com>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
> ---
>  mm/page_alloc.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)

Wasn't this patch reverted in Linus's tree for causing a regression on
some platforms? If so I'm not sure we should pull this in as a
candidate for stable should we, or am I missing something?