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Date: Thu, 21 Feb 2019 11:18:07 +0800
From: Rong Chen <rong.a.chen@...el.com>
To: Michal Hocko <mhocko@...nel.org>
Cc: Oscar Salvador <OSalvador@...e.com>,
LKML <linux-kernel@...r.kernel.org>,
Matthew Wilcox <willy@...radead.org>,
Mike Rapoport <rppt@...ux.ibm.com>, linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>, lkp@...org
Subject: Re: [LKP] [RFC PATCH] mm, memory_hotplug: fix off-by-one in
is_pageblock_removable
Hi,
The patch can fix the issue for me.
Best Regards,
Rong Chen
On 2/20/19 8:57 PM, Michal Hocko wrote:
> Rong Chen,
> coudl you double check this indeed fixes the issue for you please?
>
> On Mon 18-02-19 19:15:44, Michal Hocko wrote:
>> From: Michal Hocko <mhocko@...e.com>
>>
>> Rong Chen has reported the following boot crash
>> [ 40.305212] PGD 0 P4D 0
>> [ 40.308255] Oops: 0000 [#1] PREEMPT SMP PTI
>> [ 40.313055] CPU: 1 PID: 239 Comm: udevd Not tainted 5.0.0-rc4-00149-gefad4e4 #1
>> [ 40.321348] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>> [ 40.330813] RIP: 0010:page_mapping+0x12/0x80
>> [ 40.335709] Code: 5d c3 48 89 df e8 0e ad 02 00 85 c0 75 da 89 e8 5b 5d c3 0f 1f 44 00 00 53 48 89 fb 48 8b 43 08 48 8d 50 ff a8 01 48 0f 45 da <48> 8b 53 08 48 8d 42 ff 83 e2 01 48 0f 44 c3 48 83 38 ff 74 2f 48
>> [ 40.356704] RSP: 0018:ffff88801fa87cd8 EFLAGS: 00010202
>> [ 40.362714] RAX: ffffffffffffffff RBX: fffffffffffffffe RCX: 000000000000000a
>> [ 40.370798] RDX: fffffffffffffffe RSI: ffffffff820b9a20 RDI: ffff88801e5c0000
>> [ 40.378830] RBP: 6db6db6db6db6db7 R08: ffff88801e8bb000 R09: 0000000001b64d13
>> [ 40.386902] R10: ffff88801fa87cf8 R11: 0000000000000001 R12: ffff88801e640000
>> [ 40.395033] R13: ffffffff820b9a20 R14: ffff88801f145258 R15: 0000000000000001
>> [ 40.403138] FS: 00007fb2079817c0(0000) GS:ffff88801dd00000(0000) knlGS:0000000000000000
>> [ 40.412243] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 40.418846] CR2: 0000000000000006 CR3: 000000001fa82000 CR4: 00000000000006a0
>> [ 40.426951] Call Trace:
>> [ 40.429843] __dump_page+0x14/0x2c0
>> [ 40.433947] is_mem_section_removable+0x24c/0x2c0
>> [ 40.439327] removable_show+0x87/0xa0
>> [ 40.443613] dev_attr_show+0x25/0x60
>> [ 40.447763] sysfs_kf_seq_show+0xba/0x110
>> [ 40.452363] seq_read+0x196/0x3f0
>> [ 40.456282] __vfs_read+0x34/0x180
>> [ 40.460233] ? lock_acquire+0xb6/0x1e0
>> [ 40.464610] vfs_read+0xa0/0x150
>> [ 40.468372] ksys_read+0x44/0xb0
>> [ 40.472129] ? do_syscall_64+0x1f/0x4a0
>> [ 40.476593] do_syscall_64+0x5e/0x4a0
>> [ 40.480809] ? trace_hardirqs_off_thunk+0x1a/0x1c
>> [ 40.486195] entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> and bisected it down to efad4e475c31 ("mm, memory_hotplug:
>> is_mem_section_removable do not pass the end of a zone"). The reason for
>> the crash is that the mapping is garbage for poisoned (uninitialized) page.
>> This shouldn't happen as all pages in the zone's boundary should be
>> initialized. Later debugging revealed that the actual problem is an
>> off-by-one when evaluating the end_page. start_pfn + nr_pages resp.
>> zone_end_pfn refers to a pfn after the range and as such it might belong
>> to a differen memory section. This along with CONFIG_SPARSEMEM then
>> makes the loop condition completely bogus because a pointer arithmetic
>> doesn't work for pages from two different sections in that memory model.
>>
>> Fix the issue by reworking is_pageblock_removable to be pfn based and
>> only use struct page where necessary. This makes the code slightly
>> easier to follow and we will remove the problematic pointer arithmetic
>> completely.
>>
>> Fixes: efad4e475c31 ("mm, memory_hotplug: is_mem_section_removable do not pass the end of a zone")
>> Reported-by: <rong.a.chen@...el.com>
>> Signed-off-by: Michal Hocko <mhocko@...e.com>
>> ---
>> mm/memory_hotplug.c | 27 +++++++++++++++------------
>> 1 file changed, 15 insertions(+), 12 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 124e794867c5..1ad28323fb9f 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1188,11 +1188,13 @@ static inline int pageblock_free(struct page *page)
>> return PageBuddy(page) && page_order(page) >= pageblock_order;
>> }
>>
>> -/* Return the start of the next active pageblock after a given page */
>> -static struct page *next_active_pageblock(struct page *page)
>> +/* Return the pfn of the start of the next active pageblock after a given pfn */
>> +static unsigned long next_active_pageblock(unsigned long pfn)
>> {
>> + struct page *page = pfn_to_page(pfn);
>> +
>> /* Ensure the starting page is pageblock-aligned */
>> - BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1));
>> + BUG_ON(pfn & (pageblock_nr_pages - 1));
>>
>> /* If the entire pageblock is free, move to the end of free page */
>> if (pageblock_free(page)) {
>> @@ -1200,16 +1202,16 @@ static struct page *next_active_pageblock(struct page *page)
>> /* be careful. we don't have locks, page_order can be changed.*/
>> order = page_order(page);
>> if ((order < MAX_ORDER) && (order >= pageblock_order))
>> - return page + (1 << order);
>> + return pfn + (1 << order);
>> }
>>
>> - return page + pageblock_nr_pages;
>> + return pfn + pageblock_nr_pages;
>> }
>>
>> -static bool is_pageblock_removable_nolock(struct page *page)
>> +static bool is_pageblock_removable_nolock(unsigned long pfn)
>> {
>> + struct page *page = pfn_to_page(pfn);
>> struct zone *zone;
>> - unsigned long pfn;
>>
>> /*
>> * We have to be careful here because we are iterating over memory
>> @@ -1232,13 +1234,14 @@ static bool is_pageblock_removable_nolock(struct page *page)
>> /* Checks if this range of memory is likely to be hot-removable. */
>> bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages)
>> {
>> - struct page *page = pfn_to_page(start_pfn);
>> - unsigned long end_pfn = min(start_pfn + nr_pages, zone_end_pfn(page_zone(page)));
>> - struct page *end_page = pfn_to_page(end_pfn);
>> + unsigned long end_pfn, pfn;
>> +
>> + end_pfn = min(start_pfn + nr_pages,
>> + zone_end_pfn(page_zone(pfn_to_page(start_pfn))));
>>
>> /* 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))
>> + for (pfn = start_pfn; pfn < end_pfn; pfn = next_active_pageblock(pfn)) {
>> + if (!is_pageblock_removable_nolock(pfn))
>> return false;
>> cond_resched();
>> }
>> --
>> 2.20.1
>>
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