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Violators will be prosecuted for from ; Mon, 5 Nov 2018 15:04:07 -0000 From: Mikhail Zaslonko Subject: [PATCH v2 1/1] memory_hotplug: fix the panic when memory end is not on the section boundary Date: Mon, 5 Nov 2018 16:04:01 +0100 In-Reply-To: <20181105150401.97287-1-zaslonko@linux.ibm.com> References: <20181105150401.97287-1-zaslonko@linux.ibm.com> Message-Id: <20181105150401.97287-2-zaslonko@linux.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, Pavel.Tatashin@microsoft.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, gerald.schaefer@de.ibm.com, zaslonko@linux.ibm.com 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 pages 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_PGFLAGS=y kernel parameter mem=2050M -------------------------- page:000003d082008000 is uninitialized and poisoned page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) Call Trace: ([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160) [<00000000008f15c4>] show_valid_zones+0x5c/0x190 [<00000000008cf9c4>] dev_attr_show+0x34/0x70 [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 [<00000000003e4194>] seq_read+0x204/0x480 [<00000000003b53ea>] __vfs_read+0x32/0x178 [<00000000003b55b2>] vfs_read+0x82/0x138 [<00000000003b5be2>] ksys_read+0x5a/0xb0 [<0000000000b86ba0>] system_call+0xdc/0x2d8 Last Breaking-Event-Address: [<0000000000385b26>] test_pages_in_a_zone+0xde/0x160 Kernel panic - not syncing: Fatal exception: panic_on_oops CONFIG_DEBUG_VM_PGFLAGS=y kernel parameter mem=3075M -------------------------- page:000003d08300c000 is uninitialized and poisoned page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) Call Trace: ([<000000000038596c>] is_mem_section_removable+0xb4/0x190) [<00000000008f12fa>] show_mem_removable+0x9a/0xd8 [<00000000008cf9c4>] dev_attr_show+0x34/0x70 [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 [<00000000003e4194>] seq_read+0x204/0x480 [<00000000003b53ea>] __vfs_read+0x32/0x178 [<00000000003b55b2>] vfs_read+0x82/0x138 [<00000000003b5be2>] ksys_read+0x5a/0xb0 [<0000000000b86ba0>] system_call+0xdc/0x2d8 Last Breaking-Event-Address: [<000000000038596c>] is_mem_section_removable+0xb4/0x190 Kernel panic - not syncing: Fatal exception: panic_on_oops This fix checks if the page lies within the zone boundaries before accessing the struct page data. The check is added to both functions. 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 38d94b703e9d..8402e70f74c2 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 + i)) + return 0; page = pfn_to_page(pfn + i); if (zone && page_zone(page) != zone) return 0; -- 2.16.4