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Date:   Fri, 10 Aug 2018 10:11:55 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC][PATCH] tracepoints: Free early tracepoints after RCU is initialized

On Fri, Aug 10, 2018 at 9:30 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
>
> When enabling trace events via the kernel command line, I hit this warning:
>
> WARNING: CPU: 0 PID: 13 at kernel/rcu/srcutree.c:236 check_init_srcu_struct+0xe/0x61
> Modules linked in:
> CPU: 0 PID: 13 Comm: watchdog/0 Not tainted 4.18.0-rc6-test+ #6
> Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 02/22/2014
> RIP: 0010:check_init_srcu_struct+0xe/0x61
> Code: 48 c7 c6 ec 8a 65 b4 e8 ff 79 fe ff 48 89 df 31 f6 e8 f2 fa ff ff 5a
> 5b 41 5c 5d c3 0f 1f 44 00 00 83 3d 68 94 b8 01 01 75 02 <0f> 0b 48 8b 87 f0
> 0a 00 00 a8 03 74 45 55 48 89 e5 41 55 41 54 4c
> RSP: 0000:ffff96eb9ea03e68 EFLAGS: 00010246
> RAX: ffff96eb962b5b01 RBX: ffffffffb4a87420 RCX: 0000000000000001
> RDX: ffffffffb3107969 RSI: ffff96eb962b5b40 RDI: ffffffffb4a87420
> RBP: ffff96eb9ea03eb0 R08: ffffabbd00cd7f48 R09: 0000000000000000
> R10: ffff96eb9ea03e68 R11: ffffffffb4a6eec0 R12: ffff96eb962b5b40
> R13: ffff96eb9ea03ef8 R14: ffffffffb3107969 R15: ffffffffb3107948
> FS:  0000000000000000(0000) GS:ffff96eb9ea00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff96eb13ab2000 CR3: 0000000192a1e001 CR4: 00000000001606f0
> Call Trace:
>  <IRQ>
>  ? __call_srcu+0x2d/0x290
>  ? rcu_process_callbacks+0x26e/0x448
>  ? allocate_probes+0x2b/0x2b
>  call_srcu+0x13/0x15
>  rcu_free_old_probes+0x1f/0x21
>  rcu_process_callbacks+0x2ed/0x448
>  __do_softirq+0x172/0x336
>  irq_exit+0x62/0xb2
>  smp_apic_timer_interrupt+0x161/0x19e
>  apic_timer_interrupt+0xf/0x20
>  </IRQ>
>
> The problem is that the enabling of trace events before RCU is set up will
> cause SRCU to give this warning. To avoid this, add a list to store probes
> that need to be freed till after RCU is initialized, and then free them
> then.
>
> Link: http://lkml.kernel.org/r/20180810113554.1df28050@gandalf.local.home
>
> Fixes: e6753f23d961d ("tracepoint: Make rcuidle tracepoint callers use SRCU")
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>

thanks,

 - Joel

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