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BUG: KCSAN: data-race in n_tty_check_unthrottle / n_tty_receive_buf_common

write to 0xffff888134dd05e8 of 4 bytes by task 25676 on cpu 1:
 tty_set_flow_change drivers/tty/tty.h:54 [inline]
 n_tty_check_throttle drivers/tty/n_tty.c:261 [inline]
 n_tty_receive_buf_common+0x4dc8/0x4e70 drivers/tty/n_tty.c:1693
 n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1703
 tiocsti drivers/tty/tty_io.c:2310 [inline]
 tty_ioctl+0x969/0x1130 drivers/tty/tty_io.c:2719
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:860
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

write to 0xffff888134dd05e8 of 4 bytes by task 25675 on cpu 0:
 __tty_set_flow_change drivers/tty/tty.h:49 [inline]
 n_tty_check_unthrottle+0x1bc/0x1d0 drivers/tty/n_tty.c:299
 n_tty_read+0xe07/0x1070 drivers/tty/n_tty.c:2214
 iterate_tty_read drivers/tty/tty_io.c:868 [inline]
 tty_read+0x19c/0x430 drivers/tty/tty_io.c:944
 call_read_iter include/linux/fs.h:2156 [inline]
 do_iter_readv_writev+0x2fb/0x380 fs/read_write.c:723
 do_iter_read+0x192/0x5d0 fs/read_write.c:786
 vfs_readv fs/read_write.c:906 [inline]
 do_readv+0x171/0x2c0 fs/read_write.c:943
 __do_sys_readv fs/read_write.c:1034 [inline]
 __se_sys_readv fs/read_write.c:1031 [inline]
 __x64_sys_readv+0x41/0x50 fs/read_write.c:1031
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000002 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 25675 Comm: syz-executor.1 Not tainted 5.16.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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