Re: [syzbot] WARNING: suspicious RCU usage in get_timespec64

[Paul E. McKenney]

On Sun, Apr 04, 2021 at 10:38:41PM +0200, Thomas Gleixner wrote:
> On Sun, Apr 04 2021 at 12:05, syzbot wrote:
> 
> Cc + ...

And a couple more...

> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    5e46d1b7 reiserfs: update reiserfs_xattrs_initialized() co..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1125f831d00000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=78ef1d159159890
> > dashboard link: https://syzkaller.appspot.com/bug?extid=88e4f02896967fe1ab0d
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+88e4f02896967fe1ab0d@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > =============================
> > WARNING: suspicious RCU usage
> > 5.12.0-rc5-syzkaller #0 Not tainted
> > -----------------------------
> > kernel/sched/core.c:8294 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
> > 3 locks held by syz-executor.4/8418:
> >  #0: 
> > ffff8880751d2b28
> >  (
> > &p->pi_lock
> > ){-.-.}-{2:2}
> > , at: try_to_wake_up+0x98/0x14a0 kernel/sched/core.c:3345
> >  #1: 
> > ffff8880b9d35258
> >  (
> > &rq->lock
> > ){-.-.}-{2:2}
> > , at: rq_lock kernel/sched/sched.h:1321 [inline]
> > , at: ttwu_queue kernel/sched/core.c:3184 [inline]
> > , at: try_to_wake_up+0x5e6/0x14a0 kernel/sched/core.c:3464
> >  #2: ffff8880b9d1f948 (&per_cpu_ptr(group->pcpu, cpu)->seq){-.-.}-{0:0}, at: psi_task_change+0x142/0x220 kernel/sched/psi.c:807

This looks similar to syzbot+dde0cc33951735441301@xxxxxxxxxxxxxxxxxxxxxxxxx
in that rcu_sleep_check() sees an RCU lock held, but the later call to
lockdep_print_held_locks() does not.  Did something change recently that
could let the ->lockdep_depth counter get out of sync with the actual
number of locks held?

							Thanx, Paul

> > stack backtrace:
> > CPU: 0 PID: 8418 Comm: syz-executor.4 Not tainted 5.12.0-rc5-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:8294
> >  __might_fault+0x6e/0x180 mm/memory.c:5018
> >  _copy_from_user+0x27/0x180 lib/usercopy.c:13
> >  copy_from_user include/linux/uaccess.h:192 [inline]
> >  get_timespec64+0x75/0x220 kernel/time/time.c:787
> >  __do_sys_clock_nanosleep kernel/time/posix-timers.c:1257 [inline]
> >  __se_sys_clock_nanosleep kernel/time/posix-timers.c:1245 [inline]
> >  __x64_sys_clock_nanosleep+0x1bb/0x430 kernel/time/posix-timers.c:1245
> >  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> >  entry_SYSCALL_64_after_hwframe+0x44/0xae
> > RIP: 0033:0x48a621
> > Code: 24 0c 89 3c 24 48 89 4c 24 18 e8 aa e7 ff ff 4c 8b 54 24 18 48 8b 54 24 10 41 89 c0 8b 74 24 0c 8b 3c 24 b8 e6 00 00 00 0f 05 <44> 89 c7 48 89 04 24 e8 e3 e7 ff ff 48 8b 04 24 eb 97 66 2e 0f 1f
> > RSP: 002b:00007fffe59fbd50 EFLAGS: 00000293 ORIG_RAX: 00000000000000e6
> > RAX: ffffffffffffffda RBX: 0000000000000294 RCX: 000000000048a621
> > RDX: 00007fffe59fbd90 RSI: 0000000000000000 RDI: 0000000000000000
> > RBP: 00007fffe59fbe2c R08: 0000000000000000 R09: 00007fffe5b8a090
> > R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000032
> > R13: 000000000005717a R14: 0000000000000003 R15: 00007fffe59fbe90
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.