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Violators will be prosecuted for from ; Tue, 11 Sep 2018 08:08:15 -0600 Subject: Re: [PATCH] memory_hotplug: fix the panic when memory end is not on the section boundary References: <20180910123527.71209-1-zaslonko@linux.ibm.com> <20180910131754.GG10951@dhcp22.suse.cz> From: Zaslonko Mikhail Date: Tue, 11 Sep 2018 16:08:09 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Message-Id: <639fd656-033b-0fdb-a182-83d4acf7fe2b@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Pasha Tatashin , Michal Hocko , Mikhail Zaslonko Cc: "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "osalvador@suse.de" , "gerald.schaefer@de.ibm.com" On 10.09.2018 15:46, Pasha Tatashin wrote: > > On 9/10/18 9:17 AM, Michal Hocko wrote: >> [Cc Pavel] >> >> On Mon 10-09-18 14:35:27, Mikhail Zaslonko wrote: >>> If memory end is not aligned with the linux memory section boundary, such >>> a section is only partly initialized. This may lead to VM_BUG_ON due to >>> uninitialized struct pages access from is_mem_section_removable() or >>> test_pages_in_a_zone() function. >>> >>> Here is one of the panic examples: >>> CONFIG_DEBUG_VM_PGFLAGS=y >>> kernel parameter mem=3075M >> OK, so the last memory section is not full and we have a partial memory >> block right? >> >>> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) >> OK, this means that the struct page is not fully initialized. Do you >> have a specific place which has triggered this assert? >> >>> ------------[ cut here ]------------ >>> Call Trace: >>> ([<000000000039b8a4>] is_mem_section_removable+0xcc/0x1c0) >>> [<00000000009558ba>] show_mem_removable+0xda/0xe0 >>> [<00000000009325fc>] dev_attr_show+0x3c/0x80 >>> [<000000000047e7ea>] sysfs_kf_seq_show+0xda/0x160 >>> [<00000000003fc4e0>] seq_read+0x208/0x4c8 >>> [<00000000003cb80e>] __vfs_read+0x46/0x180 >>> [<00000000003cb9ce>] vfs_read+0x86/0x148 >>> [<00000000003cc06a>] ksys_read+0x62/0xc0 >>> [<0000000000c001c0>] system_call+0xdc/0x2d8 >>> >>> This fix checks if the page lies within the zone boundaries before >>> accessing the struct page data. The check is added to both functions. >>> Actually similar check has already been present in >>> is_pageblock_removable_nolock() function but only after the struct page >>> is accessed. >>> >> Well, I am afraid this is not the proper solution. We are relying on the >> full pageblock worth of initialized struct pages at many other place. We >> used to do that in the past because we have initialized the full >> section but this has been changed recently. Pavel, do you have any ideas >> how to deal with this partial mem sections now? > We have: > > remove_memory() > BUG_ON(check_hotplug_memory_range(start, size)) > > That supposed to safely check for this condition: if [start, start + > size) not block size aligned (and we know block size is section > aligned), hot remove is not allowed. The problem is this check is late, > and only happens when invalid range has already passed through previous > checks. > > We could add check_hotplug_memory_range() to is_mem_section_removable(): > > is_mem_section_removable(start_pfn, nr_pages) > if (check_hotplug_memory_range(PFN_PHYS(start_pfn), PFN_PHYS(nr_pages))) > return false; > > I think it should work. I don't think so since is_mem_section_removable() is called for for the entire section. Thus [start_pfn, start_pfn + nr_pages) is always memory block aligned. > > Pavel > >>> Signed-off-by: Mikhail Zaslonko >>> Reviewed-by: Gerald Schaefer >>> Cc: >>> --- >>> mm/memory_hotplug.c | 20 +++++++++++--------- >>> 1 file changed, 11 insertions(+), 9 deletions(-) >>> >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >>> index 9eea6e809a4e..8e20e8fcc3b0 100644 >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -1229,9 +1229,8 @@ static struct page *next_active_pageblock(struct page *page) >>> return page + pageblock_nr_pages; >>> } >>> >>> -static bool is_pageblock_removable_nolock(struct page *page) >>> +static bool is_pageblock_removable_nolock(struct page *page, struct zone **zone) >>> { >>> - struct zone *zone; >>> unsigned long pfn; >>> >>> /* >>> @@ -1241,15 +1240,14 @@ static bool is_pageblock_removable_nolock(struct page *page) >>> * We have to take care about the node as well. If the node is offline >>> * its NODE_DATA will be NULL - see page_zone. >>> */ >>> - if (!node_online(page_to_nid(page))) >>> - return false; >>> - >>> - zone = page_zone(page); >>> pfn = page_to_pfn(page); >>> - if (!zone_spans_pfn(zone, pfn)) >>> + if (*zone && !zone_spans_pfn(*zone, pfn)) >>> return false; >>> + if (!node_online(page_to_nid(page))) >>> + return false; >>> + *zone = page_zone(page); >>> >>> - return !has_unmovable_pages(zone, page, 0, MIGRATE_MOVABLE, true); >>> + return !has_unmovable_pages(*zone, page, 0, MIGRATE_MOVABLE, true); >>> } >>> >>> /* Checks if this range of memory is likely to be hot-removable. */ >>> @@ -1257,10 +1255,11 @@ 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; >>> + struct zone *zone = NULL; >>> >>> /* Check the starting page of each pageblock within the range */ >>> for (; page < end_page; page = next_active_pageblock(page)) { >>> - if (!is_pageblock_removable_nolock(page)) >>> + if (!is_pageblock_removable_nolock(page, &zone)) >>> return false; >>> cond_resched(); >>> } >>> @@ -1296,6 +1295,9 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn, >>> i++; >>> if (i == MAX_ORDER_NR_PAGES || pfn + i >= end_pfn) >>> continue; >>> + /* Check if we got outside of the zone */ >>> + if (zone && !zone_spans_pfn(zone, pfn)) >>> + return 0; >>> page = pfn_to_page(pfn + i); >>> if (zone && page_zone(page) != zone) >>> return 0; >>> -- >>> 2.16.4