On Tue 28-08-18 11:05:39, Mikhail Zaslonko wrote:
> Within show_valid_zones() the function test_pages_in_a_zone() should be
> called for online memory blocks only. Otherwise it might lead to the
> VM_BUG_ON due to uninitialized struct pages (when CONFIG_DEBUG_VM_PGFLAGS
> kernel option is set):
>
> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> ------------[ cut here ]------------
> Call Trace:
> ([<000000000038f91e>] test_pages_in_a_zone+0xe6/0x168)
> [<0000000000923472>] show_valid_zones+0x5a/0x1a8
> [<0000000000900284>] dev_attr_show+0x3c/0x78
> [<000000000046f6f0>] sysfs_kf_seq_show+0xd0/0x150
> [<00000000003ef662>] seq_read+0x212/0x4b8
> [<00000000003bf202>] __vfs_read+0x3a/0x178
> [<00000000003bf3ca>] vfs_read+0x8a/0x148
> [<00000000003bfa3a>] ksys_read+0x62/0xb8
> [<0000000000bc2220>] system_call+0xdc/0x2d8
>
> That VM_BUG_ON was triggered by the page poisoning introduced in
> mm/sparse.c with the git commit d0dc12e86b31 ("mm/memory_hotplug: optimize
> memory hotplug")
> With the same commit the new 'nid' field has been added to the struct
> memory_block in order to store and later on derive the node id for offline
> pages (instead of accessing struct page which might be uninitialized). But
> one reference to nid in show_valid_zones() function has been overlooked.
> Fixed with current commit.
> Also, nr_pages will not be used any more after test_pages_in_a_zone() call,
> do not update it.
>
> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.17+
> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Signed-off-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>
Btw. this land mines which are basically impossible to find during the
review are the reason why I was not all that happy about d0dc12e86b31.
It added a margninal improvement but opened a can of warms. On the other
hand maybe we just had to open that can one day...
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
> drivers/base/memory.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index f5e560188a18..622ab8edc035 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -416,26 +416,24 @@ static ssize_t show_valid_zones(struct device *dev,
> struct zone *default_zone;
> int nid;
>
> - /*
> - * The block contains more than one zone can not be offlined.
> - * This can happen e.g. for ZONE_DMA and ZONE_DMA32
> - */
> - if (!test_pages_in_a_zone(start_pfn, start_pfn + nr_pages, &valid_start_pfn, &valid_end_pfn))
> - return sprintf(buf, "none\n");
> -
> - start_pfn = valid_start_pfn;
> - nr_pages = valid_end_pfn - start_pfn;
> -
> /*
> * Check the existing zone. Make sure that we do that only on the
> * online nodes otherwise the page_zone is not reliable
> */
> if (mem->state == MEM_ONLINE) {
> + /*
> + * The block contains more than one zone can not be offlined.
> + * This can happen e.g. for ZONE_DMA and ZONE_DMA32
> + */
> + if (!test_pages_in_a_zone(start_pfn, start_pfn + nr_pages,
> + &valid_start_pfn, &valid_end_pfn))
> + return sprintf(buf, "none\n");
> + start_pfn = valid_start_pfn;
> strcat(buf, page_zone(pfn_to_page(start_pfn))->name);
> goto out;
> }
>
> - nid = pfn_to_nid(start_pfn);
> + nid = mem->nid;
> default_zone = zone_for_pfn_range(MMOP_ONLINE_KEEP, nid, start_pfn, nr_pages);
> strcat(buf, default_zone->name);
>
> --
> 2.16.4
--
Michal Hocko
SUSE Labs
