Hi,
This is the v2 to fix cpu buffers unavailable problem after some operations on file 'tracing_cpumask' and 'snapshot', also upload its testcase. Changes show as below.
v2: - Fix compile issue reported-by kernel test robot lkp@intel.com with suggestion from Steve: - Link: https://lore.kernel.org/all/202308050731.PQutr3r0-lkp@intel.com/ - Link: https://lore.kernel.org/all/20230804125107.41d6cdb1@gandalf.local.home/
- Add a step to set tracing_on in testcase (see patch 2) and add descriptions of each step.
v1: - Link: https://lore.kernel.org/all/20230804124549.2562977-1-zhengyejian1@huawei.com...
Zheng Yejian (2): tracing: Fix cpu buffers unavailable due to 'record_disabled' messed selftests/ftrace: Add a basic testcase for snapshot
kernel/trace/trace.c | 6 ++++ .../ftrace/test.d/00basic/snapshot1.tc | 31 +++++++++++++++++++ 2 files changed, 37 insertions(+) create mode 100644 tools/testing/selftests/ftrace/test.d/00basic/snapshot1.tc
Trace ring buffer can no longer record anything after executing following commands at the shell prompt:
# cd /sys/kernel/tracing # cat tracing_cpumask fff # echo 0 > tracing_cpumask # echo 1 > snapshot # echo fff > tracing_cpumask # echo 1 > tracing_on # echo "hello world" > trace_marker -bash: echo: write error: Bad file descriptor
The root cause is that: 1. After `echo 0 > tracing_cpumask`, 'record_disabled' of cpu buffers in 'tr->array_buffer.buffer' became 1 (see tracing_set_cpumask()); 2. After `echo 1 > snapshot`, 'tr->array_buffer.buffer' is swapped with 'tr->max_buffer.buffer', then the 'record_disabled' became 0 (see update_max_tr()); 3. After `echo fff > tracing_cpumask`, the 'record_disabled' become -1; Then array_buffer and max_buffer are both unavailable due to value of 'record_disabled' is not 0.
To fix it, enable or disable both array_buffer and max_buffer at the same time in tracing_set_cpumask().
Fixes: 71babb2705e2 ("tracing: change CPU ring buffer state from tracing_cpumask") Signed-off-by: Zheng Yejian zhengyejian1@huawei.com --- kernel/trace/trace.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index b8870078ef58..b0e8eb6ea8ac 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5277,11 +5277,17 @@ int tracing_set_cpumask(struct trace_array *tr, !cpumask_test_cpu(cpu, tracing_cpumask_new)) { atomic_inc(&per_cpu_ptr(tr->array_buffer.data, cpu)->disabled); ring_buffer_record_disable_cpu(tr->array_buffer.buffer, cpu); +#ifdef CONFIG_TRACER_MAX_TRACE + ring_buffer_record_disable_cpu(tr->max_buffer.buffer, cpu); +#endif } if (!cpumask_test_cpu(cpu, tr->tracing_cpumask) && cpumask_test_cpu(cpu, tracing_cpumask_new)) { atomic_dec(&per_cpu_ptr(tr->array_buffer.data, cpu)->disabled); ring_buffer_record_enable_cpu(tr->array_buffer.buffer, cpu); +#ifdef CONFIG_TRACER_MAX_TRACE + ring_buffer_record_enable_cpu(tr->max_buffer.buffer, cpu); +#endif } } arch_spin_unlock(&tr->max_lock);
This testcase is constrived to reproduce a problem that the cpu buffers become unavailable which is due to 'record_disabled' of array_buffer and max_buffer being messed up.
Local test result after bugfix: # ./ftracetest test.d/00basic/snapshot1.tc === Ftrace unit tests === [1] Snapshot and tracing_cpumask [PASS] [2] (instance) Snapshot and tracing_cpumask [PASS]
# of passed: 2 # of failed: 0 # of unresolved: 0 # of untested: 0 # of unsupported: 0 # of xfailed: 0 # of undefined(test bug): 0
Signed-off-by: Zheng Yejian zhengyejian1@huawei.com --- .../ftrace/test.d/00basic/snapshot1.tc | 31 +++++++++++++++++++ 1 file changed, 31 insertions(+) create mode 100644 tools/testing/selftests/ftrace/test.d/00basic/snapshot1.tc
diff --git a/tools/testing/selftests/ftrace/test.d/00basic/snapshot1.tc b/tools/testing/selftests/ftrace/test.d/00basic/snapshot1.tc new file mode 100644 index 000000000000..63b76cf2a360 --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/00basic/snapshot1.tc @@ -0,0 +1,31 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: Snapshot and tracing_cpumask +# requires: trace_marker tracing_cpumask snapshot +# flags: instance + +# This testcase is constrived to reproduce a problem that the cpu buffers +# become unavailable which is due to 'record_disabled' of array_buffer and +# max_buffer being messed up. + +# Store origin cpumask +ORIG_CPUMASK=`cat tracing_cpumask` + +# Stop tracing all cpu +echo 0 > tracing_cpumask + +# Take a snapshot of the main buffer +echo 1 > snapshot + +# Restore origin cpumask, note that there should be some cpus being traced +echo ${ORIG_CPUMASK} > tracing_cpumask + +# Set tracing on +echo 1 > tracing_on + +# Write a log into buffer +echo "test input 1" > trace_marker + +# Ensure the log writed so that cpu buffers are still available +grep -q "test input 1" trace +exit 0
linux-kselftest-mirror@lists.linaro.org
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Zheng Yejian