Re: page type is 3, passed migratetype is 1 (nr=512)

[Vlastimil Babka <vbabka@suse.cz>]

On 5/30/24 1:42 PM, Johannes Weiner wrote:
> On Wed, May 29, 2024 at 09:04:25PM -0400, Johannes Weiner wrote:
>> Subject: [PATCH] mm: page_alloc: fix highatomic typing in multi-block buddies
> 
> Argh, I dropped the reserve_highatomic_pageblock() caller update when
> removing the printks right before sending out. My apologies. Here is
> the fixed version:
> 
> ---
> 
> From 6aa9498ee0d7161b0605251116d16b18cd448552 Mon Sep 17 00:00:00 2001
> From: Johannes Weiner <hannes@cmpxchg.org>
> Date: Wed, 29 May 2024 18:18:12 -0400
> Subject: [PATCH] mm: page_alloc: fix highatomic typing in multi-block buddies
> 
> Christoph reports a page allocator splat triggered by xfstests:
> 
> generic/176 214s ... [ 1204.507931] run fstests generic/176 at 2024-05-27 12:52:30
> [] XFS (nvme0n1): Mounting V5 Filesystem cd936307-415f-48a3-b99d-a2d52ae1f273
> [] XFS (nvme0n1): Ending clean mount
> [] XFS (nvme1n1): Mounting V5 Filesystem ab3ee1a4-af62-4934-9a6a-6c2fde321850
> [] XFS (nvme1n1): Ending clean mount
> [] XFS (nvme1n1): Unmounting Filesystem ab3ee1a4-af62-4934-9a6a-6c2fde321850
> [] XFS (nvme1n1): Mounting V5 Filesystem 7099b02d-9c58-4d1d-be1d-2cc472d12cd9
> [] XFS (nvme1n1): Ending clean mount
> [] ------------[ cut here ]------------
> [] page type is 3, passed migratetype is 1 (nr=512)
> [] WARNING: CPU: 0 PID: 509870 at mm/page_alloc.c:645 expand+0x1c5/0x1f0
> [] Modules linked in: i2c_i801 crc32_pclmul i2c_smbus [last unloaded: scsi_debug]
> [] CPU: 0 PID: 509870 Comm: xfs_io Not tainted 6.10.0-rc1+ #2437
> [] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [] RIP: 0010:expand+0x1c5/0x1f0
> [] Code: 05 16 70 bf 02 01 e8 ca fc ff ff 8b 54 24 34 44 89 e1 48 c7 c7 80 a2 28 83 48 89 c6 b8 01 00 3
> [] RSP: 0018:ffffc90003b2b968 EFLAGS: 00010082
> [] RAX: 0000000000000000 RBX: ffffffff83fa9480 RCX: 0000000000000000
> [] RDX: 0000000000000005 RSI: 0000000000000027 RDI: 00000000ffffffff
> [] RBP: 00000000001f2600 R08: 00000000fffeffff R09: 0000000000000001
> [] R10: 0000000000000000 R11: ffffffff83676200 R12: 0000000000000009
> [] R13: 0000000000000200 R14: 0000000000000001 R15: ffffea0007c98000
> [] FS:  00007f72ca3d5780(0000) GS:ffff8881f9c00000(0000) knlGS:0000000000000000
> [] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [] CR2: 00007f72ca1fff38 CR3: 00000001aa0c6002 CR4: 0000000000770ef0
> [] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [] DR3: 0000000000000000 DR6: 00000000ffff07f0 DR7: 0000000000000400
> [] PKRU: 55555554
> [] Call Trace:
> []  <TASK>
> []  ? __warn+0x7b/0x120
> []  ? expand+0x1c5/0x1f0
> []  ? report_bug+0x191/0x1c0
> []  ? handle_bug+0x3c/0x80
> []  ? exc_invalid_op+0x17/0x70
> []  ? asm_exc_invalid_op+0x1a/0x20
> []  ? expand+0x1c5/0x1f0
> []  ? expand+0x1c5/0x1f0
> []  __rmqueue_pcplist+0x3a9/0x730
> []  get_page_from_freelist+0x7a0/0xf00
> []  __alloc_pages_noprof+0x153/0x2e0
> []  __folio_alloc_noprof+0x10/0xa0
> []  __filemap_get_folio+0x16b/0x370
> []  iomap_write_begin+0x496/0x680
> 
> While trying to service a movable allocation (page type 1), the page
> allocator runs into a two-pageblock buddy on the movable freelist
> whose second block is typed as highatomic (page type 3).
> 
> This inconsistency is caused by the highatomic reservation system
> operating on single pageblocks, while MAX_ORDER can be bigger than
> that - in this configuration, pageblock_order is 9 while
> MAX_PAGE_ORDER is 10. The test case is observed to make several
> adjacent order-3 requests with __GFP_DIRECT_RECLAIM cleared, which
> marks the surrounding block as highatomic. Upon freeing, the blocks
> merge into an order-10 buddy. When the highatomic pool is drained
> later on, this order-10 buddy gets moved back to the movable list, but
> only the first pageblock is marked movable again. A subsequent
> expand() of this buddy warns about the tail being of a different type.
> 
> This is a long-standing bug that's surfaced by the recent block type
> warnings added to the allocator. The consequences seem mostly benign,
> it just results in odd behavior: the highatomic tail blocks are not
> properly drained, instead they end up on the movable list first, then
> go back to the highatomic list after an alloc-free cycle.
> 
> To fix this, make the highatomic reservation code aware that
> allocations/buddies can be larger than a pageblock.
> 
> While it's an old quirk, the recently added type consistency warnings
> seem to be the most prominent consequence of it. Set the Fixes: tag
> accordingly to highlight this backporting dependency.
> 
> Fixes: e0932b6c1f94 ("mm: page_alloc: consolidate free page accounting")
> Reported-by: Christoph Hellwig <hch@infradead.org>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Looks good, thanks.

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>