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BUG: KCSAN: data-race in blk_stat_add / blk_stat_timer_fn

write to 0xffffe8ffffd2e638 of 8 bytes by interrupt on cpu 0:
 blk_rq_stat_init block/blk-stat.c:23 [inline]
 blk_stat_timer_fn+0x2ce/0x3d0 block/blk-stat.c:95
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 get_current arch/x86/include/asm/current.h:15 [inline]
 get_ctx kernel/kcsan/core.c:167 [inline]
 is_atomic kernel/kcsan/core.c:172 [inline]
 should_watch kernel/kcsan/core.c:203 [inline]
 check_access kernel/kcsan/core.c:458 [inline]
 __tsan_read8+0xd1/0x100 kernel/kcsan/core.c:589
 __fget_light+0x47/0x190 fs/file.c:767
 __fdget+0x24/0x40 fs/file.c:784
 fdget include/linux/file.h:62 [inline]
 do_epoll_wait+0xbb/0x180 fs/eventpoll.c:2254
 __do_sys_epoll_wait fs/eventpoll.c:2283 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2280 [inline]
 __x64_sys_epoll_wait+0x5e/0x80 fs/eventpoll.c:2280
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffe8ffffd2e638 of 8 bytes by interrupt on cpu 1:
 blk_rq_stat_add block/blk-stat.c:45 [inline]
 blk_stat_add+0x180/0x2c0 block/blk-stat.c:74
 __blk_mq_end_request+0x22d/0x270 block/blk-mq.c:527
 scsi_end_request+0x1dd/0x360 drivers/scsi/scsi_lib.c:610
 scsi_io_completion+0x11d/0xc80 drivers/scsi/scsi_lib.c:960
 scsi_finish_command+0x283/0x380 drivers/scsi/scsi.c:228
 scsi_softirq_done+0x259/0x280 drivers/scsi/scsi_lib.c:1476
 blk_done_softirq+0x1eb/0x250 block/blk-softirq.c:37
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 do_IRQ+0x81/0x130 arch/x86/kernel/irq.c:263
 ret_from_intr+0x0/0x21
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:752 [inline]
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
 _raw_spin_unlock_irqrestore+0x51/0x80 kernel/locking/spinlock.c:191
 spin_unlock_irqrestore include/linux/spinlock.h:393 [inline]
 __test_set_page_writeback+0x41d/0x7d0 mm/page-writeback.c:2801
 set_page_writeback include/linux/page-flags.h:542 [inline]
 ext4_bio_write_page+0x157/0xb4e fs/ext4/page-io.c:458
 mpage_submit_page+0xe4/0x1a0 fs/ext4/inode.c:2075
 mpage_map_and_submit_buffers+0x3c4/0x6c0 fs/ext4/inode.c:2319
 mpage_map_and_submit_extent fs/ext4/inode.c:2458 [inline]
 ext4_writepages+0x1449/0x2500 fs/ext4/inode.c:2771
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __filemap_fdatawrite_range+0x1c5/0x230 mm/filemap.c:421
 file_write_and_wait_range+0xfd/0x160 mm/filemap.c:782
 ext4_sync_file+0x266/0xaf0 fs/ext4/fsync.c:153
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2856 [inline]
 ext4_buffered_write_iter+0x222/0x290 fs/ext4/file.c:259
 ext4_file_write_iter+0xf4/0xd40 fs/ext4/file.c:547
 call_write_iter include/linux/fs.h:1902 [inline]
 new_sync_write+0x388/0x4a0 fs/read_write.c:483
 __vfs_write+0xb1/0xc0 fs/read_write.c:496
 vfs_write fs/read_write.c:558 [inline]
 vfs_write+0x18a/0x390 fs/read_write.c:542
 ksys_write+0xd5/0x1b0 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x4c/0x60 fs/read_write.c:620
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 31070 Comm: syz-executor.4 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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