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

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