tracing/ring-buffer: Clear all memory mapped CPU ring buffers on first recording

The events of a memory mapped ring buffer from the previous boot should
not be mixed in with events from the current boot. There's meta data that
is used to handle KASLR so that function names can be shown properly.

Also, since the timestamps of the previous boot have no meaning to the
timestamps of the current boot, having them intermingled in a buffer can
also cause confusion because there could possibly be events in the future.

When a trace is activated the meta data is reset so that the pointers of
are now processed for the new address space. The trace buffers are reset
when tracing starts for the first time. The problem here is that the reset
only happens on online CPUs. If a CPU is offline, it does not get reset.

To demonstrate the issue, a previous boot had tracing enabled in the boot
mapped ring buffer on reboot. On the following boot, tracing has not been
started yet so the function trace from the previous boot is still visible.

 # trace-cmd show -B boot_mapped -c 3 | tail
          <idle>-0       [003] d.h2.   156.462395: __rcu_read_lock <-cpu_emergency_disable_virtualization
          <idle>-0       [003] d.h2.   156.462396: vmx_emergency_disable_virtualization_cpu <-cpu_emergency_disable_virtualization
          <idle>-0       [003] d.h2.   156.462396: __rcu_read_unlock <-__sysvec_reboot
          <idle>-0       [003] d.h2.   156.462397: stop_this_cpu <-__sysvec_reboot
          <idle>-0       [003] d.h2.   156.462397: set_cpu_online <-stop_this_cpu
          <idle>-0       [003] d.h2.   156.462397: disable_local_APIC <-stop_this_cpu
          <idle>-0       [003] d.h2.   156.462398: clear_local_APIC <-disable_local_APIC
          <idle>-0       [003] d.h2.   156.462574: mcheck_cpu_clear <-stop_this_cpu
          <idle>-0       [003] d.h2.   156.462575: mce_intel_feature_clear <-stop_this_cpu
          <idle>-0       [003] d.h2.   156.462575: lmce_supported <-mce_intel_feature_clear

Now, if CPU 3 is taken offline, and tracing is started on the memory
mapped ring buffer, the events from the previous boot in the CPU 3 ring
buffer is not reset. Now those events are using the meta data from the
current boot and produces just hex values.

 # echo 0 > /sys/devices/system/cpu/cpu3/online
 # trace-cmd start -B boot_mapped -p function
 # trace-cmd show -B boot_mapped -c 3 | tail
          <idle>-0       [003] d.h2.   156.462395: 0xffffffff9a1e3194 <-0xffffffff9a0f655e
          <idle>-0       [003] d.h2.   156.462396: 0xffffffff9a0a1d24 <-0xffffffff9a0f656f
          <idle>-0       [003] d.h2.   156.462396: 0xffffffff9a1e6bc4 <-0xffffffff9a0f7323
          <idle>-0       [003] d.h2.   156.462397: 0xffffffff9a0d12b4 <-0xffffffff9a0f732a
          <idle>-0       [003] d.h2.   156.462397: 0xffffffff9a1458d4 <-0xffffffff9a0d12e2
          <idle>-0       [003] d.h2.   156.462397: 0xffffffff9a0faed4 <-0xffffffff9a0d12e7
          <idle>-0       [003] d.h2.   156.462398: 0xffffffff9a0faaf4 <-0xffffffff9a0faef2
          <idle>-0       [003] d.h2.   156.462574: 0xffffffff9a0e3444 <-0xffffffff9a0d12ef
          <idle>-0       [003] d.h2.   156.462575: 0xffffffff9a0e4964 <-0xffffffff9a0d12ef
          <idle>-0       [003] d.h2.   156.462575: 0xffffffff9a0e3fb0 <-0xffffffff9a0e496f

Reset all CPUs when starting a boot mapped ring buffer for the first time,
and not just the online CPUs.

Fixes: 7a1d1e4b9639f ("tracing/ring-buffer: Add last_boot_info file to boot instance")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

0 files changed, 0 insertions, 0 deletions