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BUG: KCSAN: data-race in compact_finished / compaction_alloc

write to 0xffff88813fffbc08 of 8 bytes by task 10582 on cpu 1:
 reset_cached_positions mm/compaction.c:235 [inline]
 __compact_finished mm/compaction.c:2001 [inline]
 compact_finished+0x169/0x640 mm/compaction.c:2106
 compact_zone+0x1848/0x1d60 mm/compaction.c:2317
 compact_node+0xe4/0x1e0 mm/compaction.c:2634
 compact_nodes mm/compaction.c:2650 [inline]
 sysctl_compaction_handler+0x47/0x90 mm/compaction.c:2671
 proc_sys_call_handler+0x3d3/0x520 fs/proc/proc_sysctl.c:591
 proc_sys_write+0x1e/0x30 fs/proc/proc_sysctl.c:617
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x6f0/0x7e0 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88813fffbc08 of 8 bytes by task 10580 on cpu 0:
 update_pageblock_skip mm/compaction.c:459 [inline]
 isolate_freepages mm/compaction.c:1572 [inline]
 compaction_alloc+0x1262/0x1520 mm/compaction.c:1625
 unmap_and_move+0x113/0x690 mm/migrate.c:1190
 migrate_pages+0x2f7/0xfa0 mm/migrate.c:1466
 compact_zone+0x1596/0x1d60 mm/compaction.c:2358
 compact_node+0xe4/0x1e0 mm/compaction.c:2634
 compact_nodes mm/compaction.c:2650 [inline]
 sysctl_compaction_handler+0x47/0x90 mm/compaction.c:2671
 proc_sys_call_handler+0x3d3/0x520 fs/proc/proc_sysctl.c:591
 proc_sys_write+0x1e/0x30 fs/proc/proc_sysctl.c:617
 call_write_iter include/linux/fs.h:1901 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x6f0/0x7e0 fs/read_write.c:605
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10580 Comm: syz-executor.0 Not tainted 5.11.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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