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BUG: KCSAN: data-race in do_try_to_free_pages / shrink_node

read to 0xffff88821b673078 of 8 bytes by task 23674 on cpu 1:
 shrink_node+0x9c5/0xfe0 mm/vmscan.c:2733
 shrink_zones mm/vmscan.c:2996 [inline]
 do_try_to_free_pages+0x245/0xb60 mm/vmscan.c:3049
 try_to_free_pages+0x1f5/0x4a0 mm/vmscan.c:3288
 __perform_reclaim mm/page_alloc.c:4124 [inline]
 __alloc_pages_direct_reclaim mm/page_alloc.c:4145 [inline]
 __alloc_pages_slowpath+0x45c/0xee0 mm/page_alloc.c:4562
 __alloc_pages_nodemask+0x2c8/0x310 mm/page_alloc.c:4776
 alloc_pages_vma+0xc1/0x3a0 mm/mempolicy.c:2170
 alloc_zeroed_user_highpage_movable include/linux/highmem.h:208 [inline]
 do_anonymous_page mm/memory.c:3098 [inline]
 handle_pte_fault mm/memory.c:3943 [inline]
 __handle_mm_fault+0x1940/0x2e00 mm/memory.c:4075
 handle_mm_fault+0x21b/0x530 mm/memory.c:4112
 do_user_addr_fault arch/x86/mm/fault.c:1441 [inline]
 __do_page_fault+0x456/0x8d0 arch/x86/mm/fault.c:1506
 do_page_fault+0x38/0x194 arch/x86/mm/fault.c:1530
 page_fault+0x34/0x40 arch/x86/entry/entry_64.S:1203

write to 0xffff88821b673078 of 8 bytes by task 769 on cpu 0:
 snapshot_refaults mm/vmscan.c:3013 [inline]
 do_try_to_free_pages+0x75f/0xb60 mm/vmscan.c:3072
 try_to_free_pages+0x1f5/0x4a0 mm/vmscan.c:3288
 __perform_reclaim mm/page_alloc.c:4124 [inline]
 __alloc_pages_direct_reclaim mm/page_alloc.c:4145 [inline]
 __alloc_pages_slowpath+0x45c/0xee0 mm/page_alloc.c:4562
 __alloc_pages_nodemask+0x2c8/0x310 mm/page_alloc.c:4776
 __alloc_pages include/linux/gfp.h:496 [inline]
 __alloc_pages_node include/linux/gfp.h:509 [inline]
 kmem_getpages mm/slab.c:1367 [inline]
 cache_grow_begin+0x202/0x5c0 mm/slab.c:2600
 fallback_alloc+0x161/0x1f0 mm/slab.c:3147
 ____cache_alloc_node+0x1b1/0x1c0 mm/slab.c:3215
 __do_cache_alloc mm/slab.c:3284 [inline]
 slab_alloc mm/slab.c:3312 [inline]
 kmem_cache_alloc+0x179/0x5d0 mm/slab.c:3484
 mempool_alloc_slab+0x27/0x40 mm/mempool.c:513
 mempool_alloc+0x8e/0x270 mm/mempool.c:393
 bvec_alloc+0x143/0x1e0 block/bio.c:206
 bio_alloc_bioset+0x2b7/0x3e0 block/bio.c:500
 bio_alloc include/linux/bio.h:400 [inline]
 io_submit_init_bio fs/ext4/page-io.c:406 [inline]
 io_submit_add_bh fs/ext4/page-io.c:428 [inline]
 ext4_bio_write_page+0x676/0xb4e fs/ext4/page-io.c:543
 mpage_submit_page+0xe4/0x1a0 fs/ext4/inode.c:2075
 mpage_process_page_bufs+0x3e5/0x400 fs/ext4/inode.c:2189
 mpage_prepare_extent_to_map+0x48b/0x760 fs/ext4/inode.c:2596
 ext4_writepages+0x974/0x2500 fs/ext4/inode.c:2724
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __writeback_single_inode+0xaf/0x8e0 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x4ba/0xa50 fs/fs-writeback.c:1716
 __writeback_inodes_wb+0xe8/0x1b0 fs/fs-writeback.c:1785
 wb_writeback+0x557/0x6a0 fs/fs-writeback.c:1894
 wb_check_background_flush fs/fs-writeback.c:1962 [inline]
 wb_do_writeback fs/fs-writeback.c:2050 [inline]
 wb_workfn+0x696/0x970 fs/fs-writeback.c:2078
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2264
 worker_thread+0xa0/0x800 kernel/workqueue.c:2410
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 769 Comm: kworker/u4:4 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
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