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BUG: KCSAN: data-race in balance_pgdat / shrink_node

write to 0xffff88812fffbd18 of 8 bytes by task 2485 on cpu 0:
 balance_pgdat+0x995/0xc20 mm/vmscan.c:3722
 kswapd+0x1ef/0x370 mm/vmscan.c:3926
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff88812fffbd18 of 8 bytes by task 1235 on cpu 1:
 shrink_node+0x878/0x1230 mm/vmscan.c:2752
 shrink_zones+0x2af/0x490 mm/vmscan.c:2971
 do_try_to_free_pages+0x193/0x6e0 mm/vmscan.c:3026
 try_to_free_pages+0x38e/0x8b0 mm/vmscan.c:3265
 __perform_reclaim mm/page_alloc.c:4260 [inline]
 __alloc_pages_direct_reclaim mm/page_alloc.c:4281 [inline]
 __alloc_pages_slowpath+0x55f/0x9e0 mm/page_alloc.c:4685
 __alloc_pages_nodemask+0x266/0x380 mm/page_alloc.c:4901
 alloc_pages_current+0x21d/0x310 mm/mempolicy.c:2275
 alloc_pages include/linux/gfp.h:545 [inline]
 relay_alloc_buf kernel/relay.c:136 [inline]
 relay_create_buf kernel/relay.c:177 [inline]
 relay_open_buf+0x20c/0x800 kernel/relay.c:453
 relay_open+0x31b/0x610 kernel/relay.c:605
 do_blk_trace_setup+0x306/0x550 kernel/trace/blktrace.c:557
 __blk_trace_setup kernel/trace/blktrace.c:597 [inline]
 blk_trace_setup+0x85/0x110 kernel/trace/blktrace.c:615
 sg_ioctl_common+0xa1f/0x15c0 drivers/scsi/sg.c:1120
 sg_ioctl+0x54/0xc0 drivers/scsi/sg.c:1163
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 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: 1 PID: 1235 Comm: syz-executor.2 Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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