==================================================================
BUG: KCSAN: data-race in _prb_read_valid / prb_reserve

write to 0xffffffff86f2e740 of 88 bytes by interrupt on cpu 1:
 vprintk_emit+0x1a4/0x580 kernel/printk/printk.c:2455
 x25_receive_data net/x25/x25_dev.c:43 [inline]
 x25_lapb_receive_frame+0x2d6/0x770 net/x25/x25_dev.c:127
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 fpregs_unlock arch/x86/include/asm/fpu/api.h:77 [inline]
 copy_fpstate_to_sigframe+0x306/0x7b0 arch/x86/kernel/fpu/signal.c:242
 get_sigframe+0x34f/0x470 arch/x86/kernel/signal.c:163
 x64_setup_rt_frame+0xa7/0x4e0 arch/x86/kernel/signal_64.c:175
 setup_rt_frame arch/x86/kernel/signal.c:250 [inline]
 handle_signal arch/x86/kernel/signal.c:294 [inline]
 arch_do_signal_or_restart+0x27c/0x480 arch/x86/kernel/signal.c:339
 __exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
 exit_to_user_mode_loop+0x15d/0x8c0 kernel/entry/common.c:101

read to 0xffffffff86f2e740 of 8 bytes by task 29 on cpu 0:
 desc_read kernel/printk/printk_ringbuffer.c:499 [inline]
 prb_first_seq kernel/printk/printk_ringbuffer.c:2014 [inline]
 _prb_read_valid+0x636/0x8f0 kernel/printk/printk_ringbuffer.c:2171
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
CPU: 0 UID: 0 PID: 29 Comm: pr/ttyS0 Tainted: G        W           syzkaller #0 PREEMPT(lazy)