Re: [PATCH] Correct zone boundary handling when resetting pageblock skip hints

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 03/27/2019 02:24 PM, Mel Gorman wrote:
> Mikhail Gavrilo reported the following bug being triggered in a Fedora
> kernel based on 5.1-rc1 but it is relevant to a vanilla kernel.
> 
>  kernel: page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>  kernel: ------------[ cut here ]------------
>  kernel: kernel BUG at include/linux/mm.h:1021!
>  kernel: invalid opcode: 0000 [#1] SMP NOPTI
>  kernel: CPU: 6 PID: 116 Comm: kswapd0 Tainted: G         C        5.1.0-0.rc1.git1.3.fc31.x86_64 #1
>  kernel: Hardware name: System manufacturer System Product Name/ROG STRIX X470-I GAMING, BIOS 1201 12/07/2018
>  kernel: RIP: 0010:__reset_isolation_pfn+0x244/0x2b0
>  kernel: Code: fe 06 e8 0f 8e fc ff 44 0f b6 4c 24 04 48 85 c0 0f 85 dc fe ff ff e9 68 fe ff ff 48 c7 c6 58 b7 2e 8c 4c 89 ff e8 0c 75 00 00 <0f> 0b 48 c7 c6 58 b7 2e 8c e8 fe 74 00 00 0f 0b 48 89 fa 41 b8 01
>  kernel: RSP: 0018:ffff9e2d03f0fde8 EFLAGS: 00010246
>  kernel: RAX: 0000000000000034 RBX: 000000000081f380 RCX: ffff8cffbddd6c20
>  kernel: RDX: 0000000000000000 RSI: 0000000000000006 RDI: ffff8cffbddd6c20
>  kernel: RBP: 0000000000000001 R08: 0000009898b94613 R09: 0000000000000000
>  kernel: R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000100000
>  kernel: R13: 0000000000100000 R14: 0000000000000001 R15: ffffca7de07ce000
>  kernel: FS:  0000000000000000(0000) GS:ffff8cffbdc00000(0000) knlGS:0000000000000000
>  kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  kernel: CR2: 00007fc1670e9000 CR3: 00000007f5276000 CR4: 00000000003406e0
>  kernel: Call Trace:
>  kernel:  __reset_isolation_suitable+0x62/0x120
>  kernel:  reset_isolation_suitable+0x3b/0x40
>  kernel:  kswapd+0x147/0x540
>  kernel:  ? finish_wait+0x90/0x90
>  kernel:  kthread+0x108/0x140
>  kernel:  ? balance_pgdat+0x560/0x560
>  kernel:  ? kthread_park+0x90/0x90
>  kernel:  ret_from_fork+0x27/0x50
> 
> He bisected it down to commit e332f741a8dd ("mm, compaction: be selective
> about what pageblocks to clear skip hints"). The problem is that the patch
> in question was sloppy with respect to the handling of zone boundaries. In
> some instances, it was possible for PFNs outside of a zone to be examined
> and if those were not properly initialised or poisoned then it would
> trigger the VM_BUG_ON. This patch corrects the zone boundary issues when
> resetting pageblock skip hints and Mikhail reported that the bug did not
> trigger after 30 hours of testing.
> 
> Fixes: e332f741a8dd ("mm, compaction: be selective about what pageblocks to clear skip hints")
> Reported-and-tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> ---
>  mm/compaction.c | 27 +++++++++++++++++----------
>  1 file changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index f171a83707ce..b4930bf93c8a 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -242,6 +242,7 @@ __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
>  							bool check_target)
>  {
>  	struct page *page = pfn_to_online_page(pfn);
> +	struct page *block_page;
>  	struct page *end_page;
>  	unsigned long block_pfn;
>  
> @@ -267,20 +268,26 @@ __reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
>  	    get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
>  		return false;
>  
> +	/* Ensure the start of the pageblock or zone is online and valid */
> +	block_pfn = pageblock_start_pfn(pfn);
> +	block_page = pfn_to_online_page(max(block_pfn, zone->zone_start_pfn));
> +	if (block_page) {
> +		page = block_page;
> +		pfn = block_pfn;
> +	}
> +
> +	/* Ensure the end of the pageblock or zone is online and valid */
> +	block_pfn += pageblock_nr_pages;
> +	block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
> +	end_page = pfn_to_online_page(block_pfn);
> +	if (!end_page)
> +		return false;

Should not we check zone against page_zone() from both start and end page here.