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BUG: KCSAN: data-race in del_timer / detach_if_pending

write to 0xffff888103d379b8 of 8 bytes by task 7975 on cpu 1:
 __hlist_del include/linux/list.h:764 [inline]
 detach_timer kernel/time/timer.c:815 [inline]
 detach_if_pending+0xcd/0x290 kernel/time/timer.c:832
 del_timer kernel/time/timer.c:1200 [inline]
 del_timer+0x67/0xb0 kernel/time/timer.c:1190
 try_to_grab_pending+0x22d/0x3e0 kernel/workqueue.c:1246
 mod_delayed_work_on+0x50/0x100 kernel/workqueue.c:1703
 mod_delayed_work include/linux/workqueue.h:524 [inline]
 wb_wakeup+0x89/0x90 fs/fs-writeback.c:156
 wb_start_writeback fs/fs-writeback.c:1095 [inline]
 __wakeup_flusher_threads_bdi.part.0+0xf2/0x160 fs/fs-writeback.c:2113
 __wakeup_flusher_threads_bdi fs/fs-writeback.c:2109 [inline]
 wakeup_flusher_threads+0x117/0x1b0 fs/fs-writeback.c:2139
 shrink_inactive_list+0x8bb/0x920 mm/vmscan.c:1992
 shrink_list mm/vmscan.c:2178 [inline]
 shrink_lruvec+0x4c8/0xd20 mm/vmscan.c:2496
 shrink_node_memcgs mm/vmscan.c:2685 [inline]
 shrink_node+0x2fe/0xfe0 mm/vmscan.c:2791
 shrink_zones mm/vmscan.c:2996 [inline]
 do_try_to_free_pages+0x245/0xb60 mm/vmscan.c:3049
 try_to_free_mem_cgroup_pages+0x205/0x4d0 mm/vmscan.c:3371
 reclaim_high.constprop.0+0xf7/0x140 mm/memcontrol.c:2232
 mem_cgroup_handle_over_high+0x96/0x180 mm/memcontrol.c:2313
 tracehook_notify_resume include/linux/tracehook.h:197 [inline]
 exit_to_usermode_loop+0x20c/0x2c0 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x384/0x3a0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888103d379b8 of 8 bytes by task 7961 on cpu 0:
 del_timer+0x3b/0xb0 kernel/time/timer.c:1198
 try_to_grab_pending+0x22d/0x3e0 kernel/workqueue.c:1246
 mod_delayed_work_on+0x50/0x100 kernel/workqueue.c:1703
 mod_delayed_work include/linux/workqueue.h:524 [inline]
 wb_wakeup+0x89/0x90 fs/fs-writeback.c:156
 wb_start_writeback fs/fs-writeback.c:1095 [inline]
 __wakeup_flusher_threads_bdi.part.0+0xf2/0x160 fs/fs-writeback.c:2113
 __wakeup_flusher_threads_bdi fs/fs-writeback.c:2109 [inline]
 wakeup_flusher_threads+0x117/0x1b0 fs/fs-writeback.c:2139
 shrink_inactive_list+0x8bb/0x920 mm/vmscan.c:1992
 shrink_list mm/vmscan.c:2178 [inline]
 shrink_lruvec+0x4c8/0xd20 mm/vmscan.c:2496
 shrink_node_memcgs mm/vmscan.c:2685 [inline]
 shrink_node+0x2fe/0xfe0 mm/vmscan.c:2791
 shrink_zones mm/vmscan.c:2996 [inline]
 do_try_to_free_pages+0x245/0xb60 mm/vmscan.c:3049
 try_to_free_mem_cgroup_pages+0x205/0x4d0 mm/vmscan.c:3371
 reclaim_high.constprop.0+0xf7/0x140 mm/memcontrol.c:2232
 mem_cgroup_handle_over_high+0x96/0x180 mm/memcontrol.c:2313
 tracehook_notify_resume include/linux/tracehook.h:197 [inline]
 exit_to_usermode_loop+0x20c/0x2c0 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x384/0x3a0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7961 Comm: syz-executor.1 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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