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BUG: KCSAN: data-race in do_try_to_free_pages / shrink_node

read to 0xffff88821b673078 of 8 bytes by task 7722 on cpu 0:
 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_current+0xd1/0x170 mm/mempolicy.c:2207
 alloc_pages include/linux/gfp.h:532 [inline]
 relay_alloc_buf kernel/relay.c:136 [inline]
 relay_create_buf kernel/relay.c:177 [inline]
 relay_open_buf.part.0+0x219/0x690 kernel/relay.c:452
 relay_open_buf kernel/relay.c:449 [inline]
 relay_open kernel/relay.c:599 [inline]
 relay_open+0x381/0x630 kernel/relay.c:563
 do_blk_trace_setup+0x2aa/0x5f0 kernel/trace/blktrace.c:525
 __blk_trace_setup+0x81/0x110 kernel/trace/blktrace.c:570
 blk_trace_ioctl+0xe2/0x1d0 kernel/trace/blktrace.c:709
 blkdev_ioctl+0xc6/0x1260 block/ioctl.c:568
 block_ioctl+0x95/0xc0 fs/block_dev.c:1983
 vfs_ioctl fs/ioctl.c:47 [inline]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x84f/0xcf0 fs/ioctl.c:732
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:749
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:754
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88821b673078 of 8 bytes by task 7940 on cpu 1:
 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_current+0xd1/0x170 mm/mempolicy.c:2207
 alloc_pages include/linux/gfp.h:532 [inline]
 __page_cache_alloc mm/filemap.c:981 [inline]
 __page_cache_alloc+0x183/0x1a0 mm/filemap.c:966
 pagecache_get_page+0x24b/0x6f0 mm/filemap.c:1671
 filemap_fault+0xc95/0x10a0 mm/filemap.c:2510
 ext4_filemap_fault+0x59/0x72 fs/ext4/inode.c:5977
 __do_fault+0xae/0x1f0 mm/memory.c:3188
 do_read_fault mm/memory.c:3585 [inline]
 do_fault mm/memory.c:3714 [inline]
 handle_pte_fault mm/memory.c:3945 [inline]
 __handle_mm_fault+0x270d/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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7940 Comm: syz-fuzzer Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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