On Thu, Jun 27, 2019 at 11:40 AM Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > > On 2019-06-27 11:37:10 [-0400], Joel Fernandes wrote: > > Sebastian it would be nice if possible to trace where the > > t->rcu_read_unlock_special is set for this scenario of calling > > rcu_read_unlock_special, to give a clear idea about whether it was > > really because of an IPI. I guess we could also add additional RCU > > debug fields to task_struct (just for debugging) to see where there > > unlock_special is set. > > > > Is there a test to reproduce this, or do I just boot an intel x86_64 > > machine with "threadirqs" and run into it? > > Do you want to send me a patch or should I send you my kvm image which > triggers the bug on boot? I could reproduce this as well just booting Linus tree with threadirqs command line and running rcutorture. In 15 seconds or so it locks up... gdb backtrace shows the recursive lock: (gdb) bt #0 queued_spin_lock_slowpath (lock=0xffff88813af16b44, val=0) at kernel/locking/qspinlock.c:381 #1 0xffffffff81a75a0f in queued_spin_lock (lock=<optimized out>) at ./include/asm-generic/qspinlock.h:81 #2 do_raw_spin_lock_flags (flags=<optimized out>, lock=<optimized out>) at ./include/linux/spinlock.h:193 #3 __raw_spin_lock_irqsave (lock=<optimized out>) at ./include/linux/spinlock_api_smp.h:119 #4 _raw_spin_lock_irqsave (lock=0xffff88813af16b44) at kernel/locking/spinlock.c:159 #5 0xffffffff81092158 in try_to_wake_up (p=0xffff88813af16400, state=3, wake_flags=0) at kernel/sched/core.c:2000 #6 0xffffffff8109265c in wake_up_process (p=<optimized out>) at kernel/sched/core.c:2114 #7 0xffffffff8106b019 in wakeup_softirqd () at kernel/softirq.c:76 #8 0xffffffff8106b8ef in raise_softirq_irqoff (nr=<optimized out>) at kernel/softirq.c:437 #9 0xffffffff810d080d in rcu_read_unlock_special (t=<optimized out>) at kernel/rcu/tree_plugin.h:632 #10 0xffffffff810d0868 in __rcu_read_unlock () at kernel/rcu/tree_plugin.h:414 #11 0xffffffff810aa58e in rcu_read_unlock () at ./include/linux/rcupdate.h:646 #12 cpuacct_charge (tsk=<optimized out>, cputime=<optimized out>) at kernel/sched/cpuacct.c:352 #13 0xffffffff81097994 in cgroup_account_cputime (delta_exec=<optimized out>, task=<optimized out>) at ./include/linux/cgroup.h:764 #14 update_curr (cfs_rq=<optimized out>) at kernel/sched/fair.c:843 #15 0xffffffff8109a882 in enqueue_entity (flags=<optimized out>, se=<optimized out>, cfs_rq=<optimized out>) at kernel/sched/fair.c:3901 #16 enqueue_task_fair (rq=<optimized out>, p=<optimized out>, flags=9) at kernel/sched/fair.c:5194 #17 0xffffffff81091699 in enqueue_task (flags=<optimized out>, p=<optimized out>, rq=<optimized out>) at kernel/sched/core.c:774 #18 activate_task (rq=0xffff88813af16b44, p=0x0 <fixed_percpu_data>, flags=<optimized out>) at kernel/sched/core.c:795 #19 0xffffffff81091a1a in ttwu_do_activate (rq=0xffff88813af16b44, p=0x0 <fixed_percpu_data>, wake_flags=0, rf=<optimized out>) at kernel/sched/core.c:1737 #20 0xffffffff810924b3 in ttwu_queue (wake_flags=<optimized out>, cpu=<optimized out>, p=<optimized out>) at kernel/sched/core.c:1882 #21 try_to_wake_up (p=0xffff88813af16400, state=<optimized out>, wake_flags=0) at kernel/sched/core.c:2092 #22 0xffffffff8109265c in wake_up_process (p=<optimized out>) at kernel/sched/core.c:2114 #23 0xffffffff8106b019 in wakeup_softirqd () at kernel/softirq.c:76 #24 0xffffffff8106b843 in invoke_softirq () at kernel/softirq.c:383 #25 irq_exit () at kernel/softirq.c:413 #26 0xffffffff81c01f8e in exiting_irq () at ./arch/x86/include/asm/apic.h:536 > > Sebastian