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BUG: KCSAN: data-race in __generic_block_fiemap / zap_other_threads

read to 0xffff888120f98720 of 8 bytes by task 16183 on cpu 1:
 __fatal_signal_pending include/linux/sched/signal.h:354 [inline]
 fatal_signal_pending include/linux/sched/signal.h:359 [inline]
 __generic_block_fiemap+0x4e9/0x590 fs/ioctl.c:421
 generic_block_fiemap+0x56/0x80 fs/ioctl.c:454
 _ext4_fiemap+0x296/0x430 fs/ext4/extents.c:5134
 ext4_fiemap+0x3e/0x60 fs/ext4/extents.c:5166
 ioctl_fiemap fs/ioctl.c:213 [inline]
 do_vfs_ioctl+0x4fb/0xc60 fs/ioctl.c:677
 ksys_ioctl+0xbd/0xe0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x4c/0x60 fs/ioctl.c:718
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888120f98720 of 8 bytes by task 16169 on cpu 0:
 sigaddset include/linux/signal.h:58 [inline]
 zap_other_threads+0xf1/0x140 kernel/signal.c:1356
 do_group_exit+0x1b7/0x1c0 kernel/exit.c:916
 __do_sys_exit_group kernel/exit.c:932 [inline]
 __se_sys_exit_group kernel/exit.c:930 [inline]
 __x64_sys_exit_group+0x2e/0x30 kernel/exit.c:930
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16169 Comm: syz-executor.1 Not tainted 5.4.0-rc6+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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