Messages in this thread | | | Date | Fri, 10 Aug 2018 10:06:35 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [RFC][PATCH] tracepoints: Free early tracepoints after RCU is initialized |
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On Fri, Aug 10, 2018 at 12:30:42PM -0400, Steven Rostedt wrote: > > From: "Steven Rostedt (VMware)" <rostedt@goodmis.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@goodmis.org>
SRCU is fully initialized by the end of the core_initcall(), so the choice of postcore_initcall() is a good one. It would be nice for call_srcu() to work at early boot, just like call_rcu() currently does, but that is not a change I will be pushing into the upcoming merge window. ;-)
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> --- > kernel/tracepoint.c | 32 ++++++++++++++++++++++++++++++++ > 1 file changed, 32 insertions(+) > > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c > index 955148d91b74..36635d1d8045 100644 > --- a/kernel/tracepoint.c > +++ b/kernel/tracepoint.c > @@ -53,6 +53,9 @@ static LIST_HEAD(tracepoint_module_list); > */ > static DEFINE_MUTEX(tracepoints_mutex); > > +static struct rcu_head *early_probes; > +static bool ok_to_free_tracepoints; > + > /* > * Note about RCU : > * It is used to delay the free of multiple probes array until a quiescent > @@ -80,11 +83,40 @@ static void rcu_free_old_probes(struct rcu_head *head) > call_srcu(&tracepoint_srcu, head, srcu_free_old_probes); > } > > +static __init int release_early_probes(void) > +{ > + struct rcu_head *tmp; > + > + ok_to_free_tracepoints = true; > + > + while (early_probes) { > + tmp = early_probes; > + early_probes = tmp->next; > + call_rcu_sched(tmp, rcu_free_old_probes); > + } > + > + return 0; > +} > + > +/* RCU is initialized at core_initcall */ > +postcore_initcall(release_early_probes); > + > static inline void release_probes(struct tracepoint_func *old) > { > if (old) { > struct tp_probes *tp_probes = container_of(old, > struct tp_probes, probes[0]); > + > + /* > + * We can't free probes if RCU is not initialized yet. > + * Postpone the freeing till after RCU is initialized. > + */ > + if (unlikely(!ok_to_free_tracepoints)) { > + tp_probes->rcu.next = early_probes; > + early_probes = &tp_probes->rcu; > + return; > + } > + > /* > * Tracepoint probes are protected by both sched RCU and SRCU, > * by calling the SRCU callback in the sched RCU callback we > -- > 2.13.6 >
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