pkg/report: don't blame kcov

kcov frame can be present in rcu stalls, ignore it.

pkg/report/linux.go

@@ -61,6 +61,7 @@ func ctorLinux(kernelSrc, kernelObj string, symbols map[string][]symbolizer.Symb
 		regexp.MustCompile(`^virt/lib/.*`),
 		regexp.MustCompile(`^mm/kasan/.*`),
 		regexp.MustCompile(`^mm/kmsan/.*`),
+		regexp.MustCompile(`^kernel/kcov.c`),
 		regexp.MustCompile(`^mm/sl.b.c`),
 		regexp.MustCompile(`^mm/percpu.*`),
 		regexp.MustCompile(`^mm/vmalloc.c`),

pkg/report/testdata/linux/guilty/36

@@ -0,0 +1,63 @@
+FILE: sound/core/pcm_native.c
+
+syz-executor1 (6140) used greatest stack depth: 11720 bytes left
+INFO: rcu_sched self-detected stall on CPU
+        1-....: (124998 ticks this GP) idle=0b2/1/4611686018427387906 softirq=15730/15730 fqs=31205
+         (t=125000 jiffies g=8316 c=8315 q=1529)
+NMI backtrace for cpu 1
+CPU: 1 PID: 6087 Comm: syz-executor0 Not tainted 4.16.0+ #3
+Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
+Call Trace:
+ <IRQ>
+ __dump_stack lib/dump_stack.c:77 [inline]
+ dump_stack+0x1b9/0x294 lib/dump_stack.c:113
+ nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
+ nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
+ arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
+ trigger_single_cpu_backtrace include/linux/nmi.h:156 [inline]
+ rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1376
+ print_cpu_stall kernel/rcu/tree.c:1525 [inline]
+ check_cpu_stall.isra.61.cold.80+0x36c/0x59a kernel/rcu/tree.c:1593
+ __rcu_pending kernel/rcu/tree.c:3356 [inline]
+ rcu_pending kernel/rcu/tree.c:3401 [inline]
+ rcu_check_callbacks+0x21b/0xad0 kernel/rcu/tree.c:2763
+ update_process_times+0x2d/0x70 kernel/time/timer.c:1636
+ tick_sched_handle+0xa0/0x180 kernel/time/tick-sched.c:171
+ tick_sched_timer+0x42/0x130 kernel/time/tick-sched.c:1179
+ __run_hrtimer kernel/time/hrtimer.c:1337 [inline]
+ __hrtimer_run_queues+0x3e3/0x10a0 kernel/time/hrtimer.c:1399
+ hrtimer_interrupt+0x286/0x650 kernel/time/hrtimer.c:1457
+ local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
+ smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
+ apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:862
+ </IRQ>
+RIP: 0010:__sanitizer_cov_trace_pc+0x3f/0x50 kernel/kcov.c:106
+RSP: 0018:ffff8801920cf4d0 EFLAGS: 00000216 ORIG_RAX: ffffffffffffff13
+RAX: 0000000000040000 RBX: ffff8801ceb61200 RCX: ffffc90001eb0000
+RDX: 0000000000040000 RSI: ffffffff859d760f RDI: ffff8801ceb61200
+RBP: ffff8801920cf4d0 R08: ffff8801b4946540 R09: 0000000000000006
+R10: ffff8801b4946540 R11: 0000000000000000 R12: ffffffff8826fa20
+R13: 0000000000000020 R14: ffff8801d3008c00 R15: ffff8801ceb61200
+ snd_pcm_stream_lock_irq+0xf/0xf0 sound/core/pcm_native.c:150
+ __snd_pcm_lib_xfer+0x345/0x1d10 sound/core/pcm_lib.c:2162
+ snd_pcm_oss_write3+0xe9/0x220 sound/core/oss/pcm_oss.c:1236
+ io_playback_transfer+0x274/0x310 sound/core/oss/io.c:47
+ snd_pcm_plug_write_transfer+0x36c/0x470 sound/core/oss/pcm_plugin.c:619
+ snd_pcm_oss_write2+0x25c/0x460 sound/core/oss/pcm_oss.c:1365
+ snd_pcm_oss_write1 sound/core/oss/pcm_oss.c:1431 [inline]
+ snd_pcm_oss_write+0x55f/0xa20 sound/core/oss/pcm_oss.c:2774
+ do_loop_readv_writev fs/read_write.c:703 [inline]
+ do_iter_write+0x491/0x5f0 fs/read_write.c:961
+ vfs_writev+0x1c7/0x330 fs/read_write.c:1004
+ do_writev+0x112/0x2f0 fs/read_write.c:1039
+ SYSC_writev fs/read_write.c:1112 [inline]
+ SyS_writev+0x27/0x30 fs/read_write.c:1109
+ do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
+ entry_SYSCALL_64_after_hwframe+0x42/0xb7
+RIP: 0033:0x4552d9
+RSP: 002b:00007f82ef52cc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
+RAX: ffffffffffffffda RBX: 00007f82ef52d6d4 RCX: 00000000004552d9
+RDX: 0000000000000001 RSI: 0000000020000180 RDI: 0000000000000015
+RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
+R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
+R13: 00000000000006cc R14: 00000000006fd3c0 R15: 0000000000000000