Re: wake_up on wait-queue called from hard-irq context in 3.10.63-rt65

[Paul E. McKenney]

On Wed, Apr 27, 2016 at 12:55:47PM +0200, Andreas Starzer wrote:
> This Bug was already fixed in rcutiny_plugin.h with changing the
> wait-queue to simple-waiter.
> 
> Found this bug with 3.10.63-rt65 in rcutree_plugin.h too. (It is not
> fixed in current 3.10-release)
> 
> SVC (hard-irq-context) for scheduling tries to wake-up wait-queue
> waiters and therefore simple-waiter is needed.
> 
> I fixed the problem for myself with this patch, but I don't know if
> this is a correct fix.

This wait queue no longer exists in mainline, but sounds like I
should recheck new code.

							Thanx, Paul

> Index: src/kernel/rcutree_plugin.h
> ===================================================================
> --- src/kernel/rcutree_plugin.h    (revision 159)
> +++ src/kernel/rcutree_plugin.h    (working copy)
> @@ -705,7 +705,8 @@
>  }
>  EXPORT_SYMBOL_GPL(synchronize_rcu);
> 
> -static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
> +/* (stz): bug#16085 replace standard wq by simple waiter for call by
> SVC context. */
> +static DEFINE_SWAIT_HEAD(sync_rcu_preempt_exp_wq);
>  static unsigned long sync_rcu_preempt_exp_count;
>  static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
> 
> @@ -762,8 +763,10 @@
>          }
>          if (rnp->parent == NULL) {
>              raw_spin_unlock_irqrestore(&rnp->lock, flags);
> -            if (wake)
> -                wake_up(&sync_rcu_preempt_exp_wq);
> +            if (wake) {
> +              /* (stz): bug#16085 replace standard wq by simple
> waiter for call by SVC context. */
> +              swait_wake(&sync_rcu_preempt_exp_wq);
> +            }
>              break;
>          }
>          mask = rnp->grpmask;
> @@ -883,8 +886,9 @@
> 
>      /* Wait for snapshotted ->blkd_tasks lists to drain. */
>      rnp = rcu_get_root(rsp);
> -    wait_event(sync_rcu_preempt_exp_wq,
> -           sync_rcu_preempt_exp_done(rnp));
> +    /* (stz): bug#16085 replace standard wq by simple waiter for call
> by SVC context. */
> +    swait_event(sync_rcu_preempt_exp_wq,
> +           sync_rcu_preempt_exp_done(rnp));
> 
>      /* Clean up and exit. */
>      smp_mb(); /* ensure expedited GP seen before counter increment. */
> 
> 
> 
> ------------------------------
> Detailed Output:
> ------------------------------
> 
> [22503.069680] BUG: sleeping function called from invalid context at
> kernel/rtmutex.c:796
> [22503.069685] in_atomic(): 1, irqs_disabled(): 0, pid: 385, name: rstpd
> [22503.069707] Preemption disabled at:[<8000e28c>] svc_preempt+0x8/0x20
> [22503.069708]
> [22503.069717] CPU: 1 PID: 385 Comm: rstpd Tainted: G           O
> 3.10.63-sp4-rt65-svn160 #6
> [22503.069723] Backtrace:
> [22503.069742] [<80011d08>] (dump_backtrace+0x0/0x108) from
> [<80011f18>] (show_stack+0x18/0x1c)
> [22503.069753]  r6:00000003 r5:8c906000 r4:00000000 r3:00000000
> [22503.069772] [<80011f00>] (show_stack+0x0/0x1c) from [<8060ce58>]
> (dump_stack+0x24/0x28)
> [22503.069794] [<8060ce34>] (dump_stack+0x0/0x28) from [<80054524>]
> (__might_sleep+0x100/0x158)
> [22503.069810] [<80054424>] (__might_sleep+0x0/0x158) from
> [<806104f4>] (rt_spin_lock+0x24/0x30)
> [22503.069816]  r5:00000001 r4:8086461c
> [22503.069831] [<806104d0>] (rt_spin_lock+0x0/0x30) from [<800565b0>]
> (__wake_up+0x2c/0x58)
> [22503.069837]  r4:8086461c r3:00000001
> [22503.069850] [<80056584>] (__wake_up+0x0/0x58) from [<80089f9c>]
> (rcu_report_exp_rnp.isra.50+0xac/0xb4)
> [22503.069861]  r7:00000001 r6:20010113 r5:00000001 r4:80864340
> [22503.069874] [<80089ef0>] (rcu_report_exp_rnp.isra.50+0x0/0xb4) from
> [<8008b9d0>] (rcu_read_unlock_special+0x138/0x1cc)
> [22503.069885]  r7:40010113 r6:80864340 r5:00000001 r4:80864340
> [22503.069897] [<8008b898>] (rcu_read_unlock_special+0x0/0x1cc) from
> [<8008bb10>] (rcu_note_context_switch+0xac/0x1fc)
> [22503.069912]  r9:00000001 r8:8c906000 r7:00000001 r6:8c3a6e80 r5:8c906008
> [22503.069912] r4:80853a38
> [22503.069924] [<8008ba64>] (rcu_note_context_switch+0x0/0x1fc) from
> [<8060eee4>] (__schedule+0x70/0x44c)
> [22503.069935] [<8060ee74>] (__schedule+0x0/0x44c) from [<8060f898>]
> (preempt_schedule_irq+0x40/0x6c)
> [22503.069947] [<8060f858>] (preempt_schedule_irq+0x0/0x6c) from
> [<8000e28c>] (svc_preempt+0x8/0x20)
> [22503.069953]  r4:800476bc r3:00000000
> [22503.069979] [<8004766c>] (__rcu_read_unlock+0x0/0x5c) from
> [<8046db5c>] (dev_queue_xmit+0x200/0x444)
> [22503.070007]  r4:8c957c00 r3:00001000
> [22503.070031] [<8046d95c>] (dev_queue_xmit+0x0/0x444) from
> [<8059f390>] (packet_sendmsg+0xb74/0xca0)
> [22503.070059] [<8059e81c>] (packet_sendmsg+0x0/0xca0) from
> [<80455a80>] (sock_sendmsg+0xb0/0xd8)
> [22503.070077] [<804559d0>] (sock_sendmsg+0x0/0xd8) from [<80458048>]
> (SyS_sendto+0xc0/0xe4)
> [22503.070104]  r7:0001d4e0 r6:8a02d440 r5:00000000 r4:00000035
> [22503.070120] [<80457f88>] (SyS_sendto+0x0/0xe4) from [<8000e680>]
> (ret_fast_syscall+0x0/0x30)
> [22503.070145]  r7:00000122 r6:00000014 r5:00000014 r4:7ed242dc
>