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Date: Thu, 22 Jul 2021 17:13:05 -0500 From: Tom Zanussi <zanussi@...nel.org> To: Steven Rostedt <rostedt@...dmis.org>, LKML <linux-kernel@...r.kernel.org> Cc: Masami Hiramatsu <mhiramat@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH] tracing: Synthetic event field_pos is an index not a boolean Hi Steve, On Wed, 2021-07-21 at 19:10 -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" <rostedt@...dmis.org> > > Performing the following: > > ># echo 'wakeup_lat s32 pid; u64 delta; char wake_comm[]' > > synthetic_events > ># echo 'hist:keys=pid:__arg__1=common_timestamp.usecs' > > events/sched/sched_waking/trigger > ># echo > 'hist:keys=next_pid:pid=next_pid,delta=common_timestamp.usecs- > $__arg__1:onmatch(sched.sched_waking).trace(wakeup_lat,$pid,$delta,pr > ev_comm)'\ > > events/sched/sched_switch/trigger > ># echo 1 > events/synthetic/enable > > Crashed the kernel: > > BUG: kernel NULL pointer dereference, address: 000000000000001b > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 0 P4D 0 > Oops: 0000 [#1] PREEMPT SMP > CPU: 7 PID: 0 Comm: swapper/7 Not tainted 5.13.0-rc5-test+ #104 > Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 > v03.03 07/14/2016 > RIP: 0010:strlen+0x0/0x20 > Code: f6 82 80 2b 0b bc 20 74 11 0f b6 50 01 48 83 c0 01 f6 82 80 2b > 0b bc > 20 75 ef c3 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 <80> 3f 00 > 74 10 > 48 89 f8 48 83 c0 01 80 38 9 f8 c3 31 > RSP: 0018:ffffaa75000d79d0 EFLAGS: 00010046 > RAX: 0000000000000002 RBX: ffff9cdb55575270 RCX: 0000000000000000 > RDX: ffff9cdb58c7a320 RSI: ffffaa75000d7b40 RDI: 000000000000001b > RBP: ffffaa75000d7b40 R08: ffff9cdb40a4f010 R09: ffffaa75000d7ab8 > R10: ffff9cdb4398c700 R11: 0000000000000008 R12: ffff9cdb58c7a320 > R13: ffff9cdb55575270 R14: ffff9cdb58c7a000 R15: 0000000000000018 > FS: 0000000000000000(0000) GS:ffff9cdb5aa00000(0000) > knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 000000000000001b CR3: 00000000c0612006 CR4: 00000000001706e0 > Call Trace: > trace_event_raw_event_synth+0x90/0x1d0 > action_trace+0x5b/0x70 > event_hist_trigger+0x4bd/0x4e0 > ? cpumask_next_and+0x20/0x30 > ? update_sd_lb_stats.constprop.0+0xf6/0x840 > ? __lock_acquire.constprop.0+0x125/0x550 > ? find_held_lock+0x32/0x90 > ? sched_clock_cpu+0xe/0xd0 > ? lock_release+0x155/0x440 > ? update_load_avg+0x8c/0x6f0 > ? enqueue_entity+0x18a/0x920 > ? __rb_reserve_next+0xe5/0x460 > ? ring_buffer_lock_reserve+0x12a/0x3f0 > event_triggers_call+0x52/0xe0 > trace_event_buffer_commit+0x1ae/0x240 > trace_event_raw_event_sched_switch+0x114/0x170 > __traceiter_sched_switch+0x39/0x50 > __schedule+0x431/0xb00 > schedule_idle+0x28/0x40 > do_idle+0x198/0x2e0 > cpu_startup_entry+0x19/0x20 > secondary_startup_64_no_verify+0xc2/0xcb > > The reason is that the dynamic events array keeps track of the field > position of the fields array, via the field_pos variable in the > synth_field structure. Unfortunately, that field is a boolean for > some > reason, which means any field_pos greater than 1 will be a bug (in > this > case it was 2). > > Cc: stable@...r.kernel.org > Fixes: bd82631d7ccdc ("tracing: Add support for dynamic strings to > synthetic events") > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org> > --- > kernel/trace/trace_synth.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/trace_synth.h b/kernel/trace/trace_synth.h > index 6e146b959dcd..4007fe95cf42 100644 > --- a/kernel/trace/trace_synth.h > +++ b/kernel/trace/trace_synth.h > @@ -14,10 +14,10 @@ struct synth_field { > char *name; > size_t size; > unsigned int offset; > + unsigned int field_pos; > bool is_signed; > bool is_string; > bool is_dynamic; > - bool field_pos; > }; > > struct synth_event { Good catch, thanks, Reviewed-by: Tom Zanussi <zanussi@...nel.org>
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