[Fixup Pavel's email - the patch is here for your reference http://lkml.kernel.org/r/20180828090539.41491-1-zaslonko@xxxxxxxxxxxxx] On Tue 28-08-18 13:25:43, Michal Hocko wrote: > 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 -- Michal Hocko SUSE Labs
