Re: [PATCH v13 3/6] tracing: Add snapshot refcount

[Vincent Donnefort <vdonnefort@google.com>]

On Tue, Jan 30, 2024 at 05:30:38PM +0800, kernel test robot wrote:
> Hi Vincent,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on 29142dc92c37d3259a33aef15b03e6ee25b0d188]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Vincent-Donnefort/ring-buffer-Zero-ring-buffer-sub-buffers/20240129-223025
> base:   29142dc92c37d3259a33aef15b03e6ee25b0d188
> patch link:    https://lore.kernel.org/r/20240129142802.2145305-4-vdonnefort%40google.com
> patch subject: [PATCH v13 3/6] tracing: Add snapshot refcount
> config: arc-randconfig-002-20240130 (https://download.01.org/0day-ci/archive/20240130/202401301740.qzZlpcYV-lkp@intel.com/config)
> compiler: arceb-elf-gcc (GCC) 13.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240130/202401301740.qzZlpcYV-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202401301740.qzZlpcYV-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>    kernel/trace/trace.c: In function 'tracing_set_tracer':
>    kernel/trace/trace.c:6644:17: error: implicit declaration of function 'tracing_disarm_snapshot_locked'; did you mean 'tracing_disarm_snapshot'? [-Werror=implicit-function-declaration]
>     6644 |                 tracing_disarm_snapshot_locked(tr);
>          |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>          |                 tracing_disarm_snapshot
> >> kernel/trace/trace.c:6648:23: error: implicit declaration of function 'tracing_arm_snapshot_locked'; did you mean 'tracing_arm_snapshot'? [-Werror=implicit-function-declaration]
>     6648 |                 ret = tracing_arm_snapshot_locked(tr);
>          |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>          |                       tracing_arm_snapshot
>    cc1: some warnings being treated as errors

Right, two tracers (hwlat and osnoise) select _only_ MAX_TRACE and not
TRACER_SNAPSHOT.

However, AFAICT, they will not call any of the swapping functions (they don't
set use_max_tr). So I suppose arm/disarm can be ommited in that case.

> 
> 
> vim +6648 kernel/trace/trace.c
> 
>   6560	
>   6561	int tracing_set_tracer(struct trace_array *tr, const char *buf)
>   6562	{
>   6563		struct tracer *t;
>   6564	#ifdef CONFIG_TRACER_MAX_TRACE
>   6565		bool had_max_tr;
>   6566	#endif
>   6567		int ret = 0;
>   6568	
>   6569		mutex_lock(&trace_types_lock);
>   6570	
>   6571		if (!tr->ring_buffer_expanded) {
>   6572			ret = __tracing_resize_ring_buffer(tr, trace_buf_size,
>   6573							RING_BUFFER_ALL_CPUS);
>   6574			if (ret < 0)
>   6575				goto out;
>   6576			ret = 0;
>   6577		}
>   6578	
>   6579		for (t = trace_types; t; t = t->next) {
>   6580			if (strcmp(t->name, buf) == 0)
>   6581				break;
>   6582		}
>   6583		if (!t) {
>   6584			ret = -EINVAL;
>   6585			goto out;
>   6586		}
>   6587		if (t == tr->current_trace)
>   6588			goto out;
>   6589	
>   6590	#ifdef CONFIG_TRACER_SNAPSHOT
>   6591		if (t->use_max_tr) {
>   6592			local_irq_disable();
>   6593			arch_spin_lock(&tr->max_lock);
>   6594			if (tr->cond_snapshot)
>   6595				ret = -EBUSY;
>   6596			arch_spin_unlock(&tr->max_lock);
>   6597			local_irq_enable();
>   6598			if (ret)
>   6599				goto out;
>   6600		}
>   6601	#endif
>   6602		/* Some tracers won't work on kernel command line */
>   6603		if (system_state < SYSTEM_RUNNING && t->noboot) {
>   6604			pr_warn("Tracer '%s' is not allowed on command line, ignored\n",
>   6605				t->name);
>   6606			goto out;
>   6607		}
>   6608	
>   6609		/* Some tracers are only allowed for the top level buffer */
>   6610		if (!trace_ok_for_array(t, tr)) {
>   6611			ret = -EINVAL;
>   6612			goto out;
>   6613		}
>   6614	
>   6615		/* If trace pipe files are being read, we can't change the tracer */
>   6616		if (tr->trace_ref) {
>   6617			ret = -EBUSY;
>   6618			goto out;
>   6619		}
>   6620	
>   6621		trace_branch_disable();
>   6622	
>   6623		tr->current_trace->enabled--;
>   6624	
>   6625		if (tr->current_trace->reset)
>   6626			tr->current_trace->reset(tr);
>   6627	
>   6628	#ifdef CONFIG_TRACER_MAX_TRACE
>   6629		had_max_tr = tr->current_trace->use_max_tr;
>   6630	
>   6631		/* Current trace needs to be nop_trace before synchronize_rcu */
>   6632		tr->current_trace = &nop_trace;
>   6633	
>   6634		if (had_max_tr && !t->use_max_tr) {
>   6635			/*
>   6636			 * We need to make sure that the update_max_tr sees that
>   6637			 * current_trace changed to nop_trace to keep it from
>   6638			 * swapping the buffers after we resize it.
>   6639			 * The update_max_tr is called from interrupts disabled
>   6640			 * so a synchronized_sched() is sufficient.
>   6641			 */
>   6642			synchronize_rcu();
>   6643			free_snapshot(tr);
>   6644			tracing_disarm_snapshot_locked(tr);
>   6645		}
>   6646	
>   6647		if (t->use_max_tr) {
> > 6648			ret = tracing_arm_snapshot_locked(tr);
>   6649			if (ret)
>   6650				goto out;
>   6651		}
>   6652	#else
>   6653		tr->current_trace = &nop_trace;
>   6654	#endif
>   6655	
>   6656		if (t->init) {
>   6657			ret = tracer_init(t, tr);
>   6658			if (ret) {
>   6659	#ifdef CONFIG_TRACER_MAX_TRACE
>   6660				if (t->use_max_tr)
>   6661					tracing_disarm_snapshot_locked(tr);
>   6662	#endif
>   6663				goto out;
>   6664			}
>   6665		}
>   6666	
>   6667		tr->current_trace = t;
>   6668		tr->current_trace->enabled++;
>   6669		trace_branch_enable(tr);
>   6670	 out:
>   6671		mutex_unlock(&trace_types_lock);
>   6672	
>   6673		return ret;
>   6674	}
>   6675	
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki