Maintain the tracing on/off setting of the ring_buffer when switching to the trace buffer snapshot. Taking a snapshot is done by swapping the backup ring buffer (max_tr_buffer). But since the tracing on/off setting is defined by the ring buffer, when swapping it, the tracing on/off setting can also be changed. This causes a strange result like below: /sys/kernel/debug/tracing # cat tracing_on 1 /sys/kernel/debug/tracing # echo 0 > tracing_on /sys/kernel/debug/tracing # cat tracing_on 0 /sys/kernel/debug/tracing # echo 1 > snapshot /sys/kernel/debug/tracing # cat tracing_on 1 /sys/kernel/debug/tracing # echo 1 > snapshot /sys/kernel/debug/tracing # cat tracing_on 0 We don't touch tracing_on, but snapshot changes tracing_on setting each time. This is an anomaly, because user doesn't know that each "ring_buffer" stores its own tracing-enable state and the snapshot is done by swapping ring buffers. Link: http://lkml.kernel.org/r/153149929558.11274.11730609978254724394.stgit@devbox
Showing the changes to kernel (2 of 3 files). Show all
Unified · Split
| @@ -3226,6 +3226,22 @@ int ring_buffer_record_is_on(struct ring_buffer *buffer) · 3225 unmodified lines | |||
| 3226 | return !atomic_read(&buffer->record_disabled); | 3226 | return !atomic_read(&buffer->record_disabled); |
| 3227 | } | 3227 | } |
| 3228 | 3228 | ||
| 3229 | /** | ||
| 3230 | * ring_buffer_record_is_set_on - return true if the ring buffer is set writable | ||
| 3231 | * @buffer: The ring buffer to see if write is set enabled | ||
| 3232 | * | ||
| 3233 | * Returns true if the ring buffer is set writable by ring_buffer_record_on(). | ||
| 3234 | * Note that this does NOT mean it is in a writable state. | ||
| 3235 | * | ||
| 3236 | * It may return true when the ring buffer has been disabled by | ||
| 3237 | * ring_buffer_record_disable(), as that is a temporary disabling of | ||
| 3238 | * the ring buffer. | ||
| 3239 | */ | ||
| 3240 | int ring_buffer_record_is_set_on(struct ring_buffer *buffer) | ||
| 3241 | { | ||
| 3242 | return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF); | ||
| 3243 | } | ||
| 3244 | |||
| 3229 | /** | 3245 | /** |
| 3230 | * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer | 3246 | * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer |
| 3231 | * @buffer: The ring buffer to stop writes to. | 3247 | * @buffer: The ring buffer to stop writes to. |
| @@ -1373,6 +1373,12 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu) · 1372 unmodified lines | |||
| 1373 | 1373 | ||
| 1374 | arch_spin_lock(&tr->max_lock); | 1374 | arch_spin_lock(&tr->max_lock); |
| 1375 | 1375 | ||
| 1376 | /* Inherit the recordable setting from trace_buffer */ | ||
| 1377 | if (ring_buffer_record_is_set_on(tr->trace_buffer.buffer)) | ||
| 1378 | ring_buffer_record_on(tr->max_buffer.buffer); | ||
| 1379 | else | ||
| 1380 | ring_buffer_record_off(tr->max_buffer.buffer); | ||
| 1381 | |||
| 1376 | swap(tr->trace_buffer.buffer, tr->max_buffer.buffer); | 1382 | swap(tr->trace_buffer.buffer, tr->max_buffer.buffer); |
| 1377 | 1383 | ||
| 1378 | __update_max_tr(tr, tsk, cpu); | 1384 | __update_max_tr(tr, tsk, cpu); |