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Adrian Hunter 1b4aa9313f perf intel-pt: Fix "context_switch event has no tid" error 
[ Upstream commit 7d537a8d2e ]

A context_switch event can have no tid because pids can be detached from
a task while the task is still running (in do_exit()). Note this won't
happen with per-task contexts because then tracing stops at
perf_event_exit_task()

If a task with no tid gets preempted, or a dying task gets preempted and
its parent releases it, when it subsequently gets switched back in,
Intel PT will not be able to determine what task is running and prints
an error "context_switch event has no tid". However, it is not really an
error because the task is in kernel space and the decoder can continue
to decode successfully. Fix by changing the error to be only a logged
message, and make allowance for tid == -1.

Example:

  Using 5.9-rc4 with Preemptible Kernel (Low-Latency Desktop) e.g.
  $ uname -r
  5.9.0-rc4
  $ grep PREEMPT .config
  # CONFIG_PREEMPT_NONE is not set
  # CONFIG_PREEMPT_VOLUNTARY is not set
  CONFIG_PREEMPT=y
  CONFIG_PREEMPT_COUNT=y
  CONFIG_PREEMPTION=y
  CONFIG_PREEMPT_RCU=y
  CONFIG_PREEMPT_NOTIFIERS=y
  CONFIG_DRM_I915_PREEMPT_TIMEOUT=640
  CONFIG_DEBUG_PREEMPT=y
  # CONFIG_PREEMPT_TRACER is not set
  # CONFIG_PREEMPTIRQ_DELAY_TEST is not set

Before:

  $ cat forkit.c

  #include <sys/types.h>
  #include <unistd.h>
  #include <sys/wait.h>

  int main()
  {
          pid_t child;
          int status = 0;

          child = fork();
          if (child == 0)
                  return 123;
          wait(&status);
          return 0;
  }

  $ gcc -o forkit forkit.c
  $ sudo ~/bin/perf record --kcore -a -m,64M -e intel_pt/cyc/k &
  [1] 11016
  $ taskset 2 ./forkit
  $ sudo pkill perf
  $ [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 17.262 MB perf.data ]

  [1]+  Terminated              sudo ~/bin/perf record --kcore -a -m,64M -e intel_pt/cyc/k
  $ sudo ~/bin/perf script --show-task-events --show-switch-events --itrace=iqqe-o -C 1 --ns | grep -C 2 forkit
  context_switch event has no tid
           taskset 11019 [001] 66663.270045029:          1 instructions:k:  ffffffffb1d9f844 strnlen_user+0xb4 ([kernel.kallsyms])
           taskset 11019 [001] 66663.270201816:          1 instructions:k:  ffffffffb1a83121 unmap_page_range+0x561 ([kernel.kallsyms])
            forkit 11019 [001] 66663.270327553: PERF_RECORD_COMM exec: forkit:11019/11019
            forkit 11019 [001] 66663.270420028:          1 instructions:k:  ffffffffb1db9537 __clear_user+0x27 ([kernel.kallsyms])
            forkit 11019 [001] 66663.270648704:          1 instructions:k:  ffffffffb18829e6 do_user_addr_fault+0xf6 ([kernel.kallsyms])
            forkit 11019 [001] 66663.270833163:          1 instructions:k:  ffffffffb230a825 irqentry_exit_to_user_mode+0x15 ([kernel.kallsyms])
            forkit 11019 [001] 66663.271092359:          1 instructions:k:  ffffffffb1aea3d9 lock_page_memcg+0x9 ([kernel.kallsyms])
            forkit 11019 [001] 66663.271207092: PERF_RECORD_FORK(11020:11020):(11019:11019)
            forkit 11019 [001] 66663.271234775: PERF_RECORD_SWITCH_CPU_WIDE OUT          next pid/tid: 11020/11020
            forkit 11020 [001] 66663.271238407: PERF_RECORD_SWITCH_CPU_WIDE IN           prev pid/tid: 11019/11019
            forkit 11020 [001] 66663.271312066:          1 instructions:k:  ffffffffb1a88140 handle_mm_fault+0x10 ([kernel.kallsyms])
            forkit 11020 [001] 66663.271476225: PERF_RECORD_EXIT(11020:11020):(11019:11019)
            forkit 11020 [001] 66663.271497488: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt  next pid/tid: 11019/11019
            forkit 11019 [001] 66663.271500523: PERF_RECORD_SWITCH_CPU_WIDE IN           prev pid/tid: 11020/11020
            forkit 11019 [001] 66663.271517241:          1 instructions:k:  ffffffffb24012cd error_entry+0x6d ([kernel.kallsyms])
            forkit 11019 [001] 66663.271664080: PERF_RECORD_EXIT(11019:11019):(1386:1386)

After:

  $ sudo ~/bin/perf script --show-task-events --show-switch-events --itrace=iqqe-o -C 1 --ns | grep -C 2 forkit
           taskset 11019 [001] 66663.270045029:          1 instructions:k:  ffffffffb1d9f844 strnlen_user+0xb4 ([kernel.kallsyms])
           taskset 11019 [001] 66663.270201816:          1 instructions:k:  ffffffffb1a83121 unmap_page_range+0x561 ([kernel.kallsyms])
            forkit 11019 [001] 66663.270327553: PERF_RECORD_COMM exec: forkit:11019/11019
            forkit 11019 [001] 66663.270420028:          1 instructions:k:  ffffffffb1db9537 __clear_user+0x27 ([kernel.kallsyms])
            forkit 11019 [001] 66663.270648704:          1 instructions:k:  ffffffffb18829e6 do_user_addr_fault+0xf6 ([kernel.kallsyms])
            forkit 11019 [001] 66663.270833163:          1 instructions:k:  ffffffffb230a825 irqentry_exit_to_user_mode+0x15 ([kernel.kallsyms])
            forkit 11019 [001] 66663.271092359:          1 instructions:k:  ffffffffb1aea3d9 lock_page_memcg+0x9 ([kernel.kallsyms])
            forkit 11019 [001] 66663.271207092: PERF_RECORD_FORK(11020:11020):(11019:11019)
            forkit 11019 [001] 66663.271234775: PERF_RECORD_SWITCH_CPU_WIDE OUT          next pid/tid: 11020/11020
            forkit 11020 [001] 66663.271238407: PERF_RECORD_SWITCH_CPU_WIDE IN           prev pid/tid: 11019/11019
            forkit 11020 [001] 66663.271312066:          1 instructions:k:  ffffffffb1a88140 handle_mm_fault+0x10 ([kernel.kallsyms])
            forkit 11020 [001] 66663.271476225: PERF_RECORD_EXIT(11020:11020):(11019:11019)
            forkit 11020 [001] 66663.271497488: PERF_RECORD_SWITCH_CPU_WIDE OUT preempt  next pid/tid: 11019/11019
            forkit 11019 [001] 66663.271500523: PERF_RECORD_SWITCH_CPU_WIDE IN           prev pid/tid: 11020/11020
            forkit 11019 [001] 66663.271517241:          1 instructions:k:  ffffffffb24012cd error_entry+0x6d ([kernel.kallsyms])
            forkit 11019 [001] 66663.271664080: PERF_RECORD_EXIT(11019:11019):(1386:1386)
            forkit 11019 [001] 66663.271688752: PERF_RECORD_SWITCH_CPU_WIDE OUT          next pid/tid:    -1/-1
               :-1    -1 [001] 66663.271692086: PERF_RECORD_SWITCH_CPU_WIDE IN           prev pid/tid: 11019/11019
                :-1    -1 [001] 66663.271707466:          1 instructions:k:  ffffffffb18eb096 update_load_avg+0x306 ([kernel.kallsyms])

Fixes: 86c2786994 ("perf intel-pt: Add support for PERF_RECORD_SWITCH")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lore.kernel.org/lkml/20200909084923.9096-3-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-10-30 10:38:19 +01:00
..
accounting tools/accounting/getdelays.c: fix netlink attribute length 2020-04-13 10:45:10 +02:00
arch jump_label: move 'asm goto' support test to Kconfig 2019-06-04 08:02:34 +02:00
bpf bpftool: Fix printing incorrect pointer in btf_dump_ptr 2020-04-29 16:31:07 +02:00
build tools build feature: Quote CC and CXX for their arguments 2020-08-21 11:05:39 +02:00
cgroup
firewire
gpio tools: gpio-hammer: Avoid potential overflow in main 2020-10-01 13:14:39 +02:00
hv Tools: hv: kvp: eliminate 'may be used uninitialized' warning 2019-09-10 10:33:50 +01:00
iio iio: iio-utils: Fix possible incorrect mask calculation 2019-07-31 07:27:02 +02:00
include perf tools: Correct SNOOPX field offset 2020-09-09 19:04:27 +02:00
kvm/kvm_stat tools/kvm_stat: Fix kvm_exit filter name 2020-02-11 04:34:08 -08:00
laptop
leds
lib tools lib traceevent: Fix memory leak in process_dynamic_array_len 2020-08-11 15:32:33 +02:00
memory-model tools/memory-model: Rename litmus tests to comply to norm7 2018-07-17 09:30:36 +02:00
nfsd
objtool objtool: Fix noreturn detection for ignored functions 2020-10-01 13:14:50 +02:00
pci tools: PCI: Fix broken pcitest compilation 2019-11-24 08:21:08 +01:00
pcmcia
perf perf intel-pt: Fix "context_switch event has no tid" error 2020-10-30 10:38:19 +01:00
power tools/power/x86/intel_pstate_tracer: changes for python 3 compatibility 2020-10-01 13:14:31 +02:00
scripts tools: Let O= makes handle a relative path with -C option 2020-04-02 15:28:17 +02:00
spi
testing selftests/x86/syscall_nt: Clear weird flags after each test 2020-10-01 13:14:49 +02:00
thermal/tmon tools/thermal: tmon: fix for segfault 2018-03-27 09:51:23 +02:00
time
usb usbip: Fix unsafe unaligned pointer usage 2020-02-24 08:34:45 +01:00
virtio virtio: fix test build after uio.h change 2019-01-13 09:51:03 +01:00
vm tools/vm: fix cross-compile build 2020-04-29 16:31:28 +02:00
wmi
Makefile