syzbot


WARNING: suspicious RCU usage in console_conditional_schedule

Status: fixed on 2021/11/10 00:50
Reported-by: syzbot+@syzkaller.appspotmail.com
Fix commit: 3066820034b5 rcu: Reject RCU_LOCKDEP_WARN() false positives
First crash: 632d, last: 632d

Sample crash report:
=============================
WARNING: suspicious RCU usage
5.13.0-rc1-syzkaller #0 Not tainted
-----------------------------
kernel/sched/core.c:8304 Illegal context switch in RCU-sched read-side critical section!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
4 locks held by agetty/8138:
 #0: ffff888028e5e098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:267
 #1: 
ffff888028e5e2e8
 (
&tty->termios_rwsem
){++++}-{3:3}
, at: n_tty_receive_buf_common+0x89/0x2bc0 drivers/tty/n_tty.c:1703
 #2: 
ffffc90000fb8378
 (
&ldata->output_lock
){+.+.}-{3:3}
, at: flush_echoes drivers/tty/n_tty.c:824 [inline]
, at: __receive_buf drivers/tty/n_tty.c:1645 [inline]
, at: n_tty_receive_buf_common+0xb49/0x2bc0 drivers/tty/n_tty.c:1740
 #3: 
ffffffff8bf68300 (console_lock){+.+.}-{0:0}
, at: do_con_write+0x10f/0x1e60 drivers/tty/vt/vt.c:2868

stack backtrace:
CPU: 0 PID: 8138 Comm: agetty Not tainted 5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x141/0x1d7 lib/dump_stack.c:120
 ___might_sleep+0x266/0x2c0 kernel/sched/core.c:8304
 console_conditional_schedule+0x37/0x50 kernel/printk/printk.c:2687
 fbcon_redraw.constprop.0+0x1aa/0x4b0 drivers/video/fbdev/core/fbcon.c:1667
 fbcon_scroll+0x1d7a/0x3580 drivers/video/fbdev/core/fbcon.c:1782
 con_scroll+0x5b9/0x6d0 drivers/tty/vt/vt.c:630
 lf+0x26b/0x2c0 drivers/tty/vt/vt.c:1490
 do_con_trol+0x20f/0x54c0 drivers/tty/vt/vt.c:2170
 do_con_write+0xdbd/0x1e60 drivers/tty/vt/vt.c:2911
 con_write+0x21/0x40 drivers/tty/vt/vt.c:3255
 do_output_char+0x5de/0x850 drivers/tty/n_tty.c:444
 __process_echoes+0x38e/0x9f0 drivers/tty/n_tty.c:736
 flush_echoes drivers/tty/n_tty.c:826 [inline]
 __receive_buf drivers/tty/n_tty.c:1645 [inline]
 n_tty_receive_buf_common+0xb88/0x2bc0 drivers/tty/n_tty.c:1740
 tiocsti drivers/tty/tty_io.c:2315 [inline]
 tty_ioctl+0x8db/0x1600 drivers/tty/tty_io.c:2721
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl fs/ioctl.c:1055 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
 do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f1747641017
Code: 00 00 00 48 8b 05 81 7e 2b 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 51 7e 2b 00 f7 d8 64 89 01 48
RSP: 002b:00007fffaea23708 EFLAGS: 00000206 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fffaea23888 RCX: 00007f1747641017
RDX: 00007fffaea23887 RSI: 0000000000005412 RDI: 0000000000000000
RBP: 00007fffaea238cf R08: ffffffffffffff98 R09: 00007fffaea23780
R10: 0000000000000000 R11: 0000000000000206 R12: 00007fffaea23724
R13: 00007fffaea23880 R14: 00007fffaea23780 R15: 0000000000000000

Crashes (1):
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets Title
ci-upstream-kasan-gce-root 2021/05/15 18:15 upstream f36edc5533b2 93f844de .config console log report info WARNING: suspicious RCU usage in console_conditional_schedule
* Struck through repros no longer work on HEAD.