Message-ID: <20241224221413.7b8c68c3@batman.local.home>
Date: Tue, 24 Dec 2024 22:14:13 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, Linux trace kernel
 <linux-trace-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Peter Zijlstra <peterz@...radead.org>, Andrew Morton
 <akpm@...ux-foundation.org>
Subject: [PATCH v2] tracing: Switch trace.c code over to use guard()

From: Steven Rostedt <rostedt@...dmis.org>

There are several functions in trace.c that have "goto out;" or
equivalent on error in order to release locks or free values that were
allocated. This can be error prone or just simply make the code more
complex.

Switch every location that ends with unlocking a mutex or freeing on error
over to using the guard(mutex)() and __free() infrastructure to let the
compiler worry about releasing locks. This makes the code easier to read
and understand.

There's one place that should probably return an error but instead return
0. This does not change the return as the only changes are to do the
conversion without changing the logic. Fixing that location will have to
come later.

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
Changes since v1: https://lore.kernel.org/20241219201344.687105470@goodmis.org

- Had a typo "guaurd" ? I think I screwed it up when sending out the patches.
  It worked fine in my repo, but when I pulled them from patchwork,
  it was broken. I sent these out with quilt, and manually review them
  before sending. I think I must have added the typo in my review :-p

 kernel/trace/trace.c | 266 +++++++++++++++----------------------------
 1 file changed, 94 insertions(+), 172 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 957f941a08e7..e6e1de69af01 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -26,6 +26,7 @@
 #include <linux/hardirq.h>
 #include <linux/linkage.h>
 #include <linux/uaccess.h>
+#include <linux/cleanup.h>
 #include <linux/vmalloc.h>
 #include <linux/ftrace.h>
 #include <linux/module.h>
@@ -535,19 +536,16 @@ LIST_HEAD(ftrace_trace_arrays);
 int trace_array_get(struct trace_array *this_tr)
 {
 	struct trace_array *tr;
-	int ret = -ENODEV;
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
 		if (tr == this_tr) {
 			tr->ref++;
-			ret = 0;
-			break;
+			return 0;
 		}
 	}
-	mutex_unlock(&trace_types_lock);
 
-	return ret;
+	return -ENODEV;
 }
 
 static void __trace_array_put(struct trace_array *this_tr)
@@ -1443,22 +1441,20 @@ EXPORT_SYMBOL_GPL(tracing_snapshot_alloc);
 int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data,
 				 cond_update_fn_t update)
 {
-	struct cond_snapshot *cond_snapshot;
-	int ret = 0;
+	struct cond_snapshot *cond_snapshot __free(kfree) =
+		kzalloc(sizeof(*cond_snapshot), GFP_KERNEL);
+	int ret;
 
-	cond_snapshot = kzalloc(sizeof(*cond_snapshot), GFP_KERNEL);
 	if (!cond_snapshot)
 		return -ENOMEM;
 
 	cond_snapshot->cond_data = cond_data;
 	cond_snapshot->update = update;
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 
-	if (tr->current_trace->use_max_tr) {
-		ret = -EBUSY;
-		goto fail_unlock;
-	}
+	if (tr->current_trace->use_max_tr)
+		return -EBUSY;
 
 	/*
 	 * The cond_snapshot can only change to NULL without the
@@ -1468,29 +1464,20 @@ int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data,
 	 * do safely with only holding the trace_types_lock and not
 	 * having to take the max_lock.
 	 */
-	if (tr->cond_snapshot) {
-		ret = -EBUSY;
-		goto fail_unlock;
-	}
+	if (tr->cond_snapshot)
+		return -EBUSY;
 
 	ret = tracing_arm_snapshot_locked(tr);
 	if (ret)
-		goto fail_unlock;
+		return ret;
 
 	local_irq_disable();
 	arch_spin_lock(&tr->max_lock);
-	tr->cond_snapshot = cond_snapshot;
+	tr->cond_snapshot = no_free_ptr(cond_snapshot);
 	arch_spin_unlock(&tr->max_lock);
 	local_irq_enable();
 
-	mutex_unlock(&trace_types_lock);
-
-	return ret;
-
- fail_unlock:
-	mutex_unlock(&trace_types_lock);
-	kfree(cond_snapshot);
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(tracing_snapshot_cond_enable);
 
@@ -2203,10 +2190,10 @@ static __init int init_trace_selftests(void)
 
 	selftests_can_run = true;
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 
 	if (list_empty(&postponed_selftests))
-		goto out;
+		return 0;
 
 	pr_info("Running postponed tracer tests:\n");
 
@@ -2235,9 +2222,6 @@ static __init int init_trace_selftests(void)
 	}
 	tracing_selftest_running = false;
 
- out:
-	mutex_unlock(&trace_types_lock);
-
 	return 0;
 }
 core_initcall(init_trace_selftests);
@@ -2807,7 +2791,7 @@ int tracepoint_printk_sysctl(const struct ctl_table *table, int write,
 	int save_tracepoint_printk;
 	int ret;
 
-	mutex_lock(&tracepoint_printk_mutex);
+	guard(mutex)(&tracepoint_printk_mutex);
 	save_tracepoint_printk = tracepoint_printk;
 
 	ret = proc_dointvec(table, write, buffer, lenp, ppos);
@@ -2820,16 +2804,13 @@ int tracepoint_printk_sysctl(const struct ctl_table *table, int write,
 		tracepoint_printk = 0;
 
 	if (save_tracepoint_printk == tracepoint_printk)
-		goto out;
+		return ret;
 
 	if (tracepoint_printk)
 		static_key_enable(&tracepoint_printk_key.key);
 	else
 		static_key_disable(&tracepoint_printk_key.key);
 
- out:
-	mutex_unlock(&tracepoint_printk_mutex);
-
 	return ret;
 }
 
@@ -5123,7 +5104,8 @@ static int tracing_trace_options_show(struct seq_file *m, void *v)
 	u32 tracer_flags;
 	int i;
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
+
 	tracer_flags = tr->current_trace->flags->val;
 	trace_opts = tr->current_trace->flags->opts;
 
@@ -5140,7 +5122,6 @@ static int tracing_trace_options_show(struct seq_file *m, void *v)
 		else
 			seq_printf(m, "no%s\n", trace_opts[i].name);
 	}
-	mutex_unlock(&trace_types_lock);
 
 	return 0;
 }
@@ -5805,7 +5786,7 @@ trace_insert_eval_map_file(struct module *mod, struct trace_eval_map **start,
 		return;
 	}
 
-	mutex_lock(&trace_eval_mutex);
+	guard(mutex)(&trace_eval_mutex);
 
 	if (!trace_eval_maps)
 		trace_eval_maps = map_array;
@@ -5829,8 +5810,6 @@ trace_insert_eval_map_file(struct module *mod, struct trace_eval_map **start,
 		map_array++;
 	}
 	memset(map_array, 0, sizeof(*map_array));
-
-	mutex_unlock(&trace_eval_mutex);
 }
 
 static void trace_create_eval_file(struct dentry *d_tracer)
@@ -5994,23 +5973,18 @@ ssize_t tracing_resize_ring_buffer(struct trace_array *tr,
 {
 	int ret;
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 
 	if (cpu_id != RING_BUFFER_ALL_CPUS) {
 		/* make sure, this cpu is enabled in the mask */
-		if (!cpumask_test_cpu(cpu_id, tracing_buffer_mask)) {
-			ret = -EINVAL;
-			goto out;
-		}
+		if (!cpumask_test_cpu(cpu_id, tracing_buffer_mask))
+			return -EINVAL;
 	}
 
 	ret = __tracing_resize_ring_buffer(tr, size, cpu_id);
 	if (ret < 0)
 		ret = -ENOMEM;
 
-out:
-	mutex_unlock(&trace_types_lock);
-
 	return ret;
 }
 
@@ -6102,9 +6076,9 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 #ifdef CONFIG_TRACER_MAX_TRACE
 	bool had_max_tr;
 #endif
-	int ret = 0;
+	int ret;
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 
 	update_last_data(tr);
 
@@ -6112,7 +6086,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 		ret = __tracing_resize_ring_buffer(tr, trace_buf_size,
 						RING_BUFFER_ALL_CPUS);
 		if (ret < 0)
-			goto out;
+			return ret;
 		ret = 0;
 	}
 
@@ -6120,12 +6094,11 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 		if (strcmp(t->name, buf) == 0)
 			break;
 	}
-	if (!t) {
-		ret = -EINVAL;
-		goto out;
-	}
+	if (!t)
+		return -EINVAL;
+
 	if (t == tr->current_trace)
-		goto out;
+		return 0;
 
 #ifdef CONFIG_TRACER_SNAPSHOT
 	if (t->use_max_tr) {
@@ -6136,27 +6109,23 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 		arch_spin_unlock(&tr->max_lock);
 		local_irq_enable();
 		if (ret)
-			goto out;
+			return ret;
 	}
 #endif
 	/* Some tracers won't work on kernel command line */
 	if (system_state < SYSTEM_RUNNING && t->noboot) {
 		pr_warn("Tracer '%s' is not allowed on command line, ignored\n",
 			t->name);
-		goto out;
+		return 0;
 	}
 
 	/* Some tracers are only allowed for the top level buffer */
-	if (!trace_ok_for_array(t, tr)) {
-		ret = -EINVAL;
-		goto out;
-	}
+	if (!trace_ok_for_array(t, tr))
+		return -EINVAL;
 
 	/* If trace pipe files are being read, we can't change the tracer */
-	if (tr->trace_ref) {
-		ret = -EBUSY;
-		goto out;
-	}
+	if (tr->trace_ref)
+		return -EBUSY;
 
 	trace_branch_disable();
 
@@ -6187,7 +6156,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 	if (!had_max_tr && t->use_max_tr) {
 		ret = tracing_arm_snapshot_locked(tr);
 		if (ret)
-			goto out;
+			return ret;
 	}
 #else
 	tr->current_trace = &nop_trace;
@@ -6200,17 +6169,15 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 			if (t->use_max_tr)
 				tracing_disarm_snapshot(tr);
 #endif
-			goto out;
+			return ret;
 		}
 	}
 
 	tr->current_trace = t;
 	tr->current_trace->enabled++;
 	trace_branch_enable(tr);
- out:
-	mutex_unlock(&trace_types_lock);
 
-	return ret;
+	return 0;
 }
 
 static ssize_t
@@ -6288,22 +6255,18 @@ tracing_thresh_write(struct file *filp, const char __user *ubuf,
 	struct trace_array *tr = filp->private_data;
 	int ret;
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 	ret = tracing_nsecs_write(&tracing_thresh, ubuf, cnt, ppos);
 	if (ret < 0)
-		goto out;
+		return ret;
 
 	if (tr->current_trace->update_thresh) {
 		ret = tr->current_trace->update_thresh(tr);
 		if (ret < 0)
-			goto out;
+			return ret;
 	}
 
-	ret = cnt;
-out:
-	mutex_unlock(&trace_types_lock);
-
-	return ret;
+	return cnt;
 }
 
 #ifdef CONFIG_TRACER_MAX_TRACE
@@ -6522,31 +6485,29 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 	 * This is just a matter of traces coherency, the ring buffer itself
 	 * is protected.
 	 */
-	mutex_lock(&iter->mutex);
+	guard(mutex)(&iter->mutex);
 
 	/* return any leftover data */
 	sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
 	if (sret != -EBUSY)
-		goto out;
+		return sret;
 
 	trace_seq_init(&iter->seq);
 
 	if (iter->trace->read) {
 		sret = iter->trace->read(iter, filp, ubuf, cnt, ppos);
 		if (sret)
-			goto out;
+			return sret;
 	}
 
 waitagain:
 	sret = tracing_wait_pipe(filp);
 	if (sret <= 0)
-		goto out;
+		return sret;
 
 	/* stop when tracing is finished */
-	if (trace_empty(iter)) {
-		sret = 0;
-		goto out;
-	}
+	if (trace_empty(iter))
+		return 0;
 
 	if (cnt >= TRACE_SEQ_BUFFER_SIZE)
 		cnt = TRACE_SEQ_BUFFER_SIZE - 1;
@@ -6610,9 +6571,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
 	if (sret == -EBUSY)
 		goto waitagain;
 
-out:
-	mutex_unlock(&iter->mutex);
-
 	return sret;
 }
 
@@ -7204,25 +7162,19 @@ u64 tracing_event_time_stamp(struct trace_buffer *buffer, struct ring_buffer_eve
  */
 int tracing_set_filter_buffering(struct trace_array *tr, bool set)
 {
-	int ret = 0;
-
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 
 	if (set && tr->no_filter_buffering_ref++)
-		goto out;
+		return 0;
 
 	if (!set) {
-		if (WARN_ON_ONCE(!tr->no_filter_buffering_ref)) {
-			ret = -EINVAL;
-			goto out;
-		}
+		if (WARN_ON_ONCE(!tr->no_filter_buffering_ref))
+			return -EINVAL;
 
 		--tr->no_filter_buffering_ref;
 	}
- out:
-	mutex_unlock(&trace_types_lock);
 
-	return ret;
+	return 0;
 }
 
 struct ftrace_buffer_info {
@@ -7298,12 +7250,10 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	if (ret)
 		return ret;
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 
-	if (tr->current_trace->use_max_tr) {
-		ret = -EBUSY;
-		goto out;
-	}
+	if (tr->current_trace->use_max_tr)
+		return -EBUSY;
 
 	local_irq_disable();
 	arch_spin_lock(&tr->max_lock);
@@ -7312,24 +7262,20 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	arch_spin_unlock(&tr->max_lock);
 	local_irq_enable();
 	if (ret)
-		goto out;
+		return ret;
 
 	switch (val) {
 	case 0:
-		if (iter->cpu_file != RING_BUFFER_ALL_CPUS) {
-			ret = -EINVAL;
-			break;
-		}
+		if (iter->cpu_file != RING_BUFFER_ALL_CPUS)
+			return -EINVAL;
 		if (tr->allocated_snapshot)
 			free_snapshot(tr);
 		break;
 	case 1:
 /* Only allow per-cpu swap if the ring buffer supports it */
 #ifndef CONFIG_RING_BUFFER_ALLOW_SWAP
-		if (iter->cpu_file != RING_BUFFER_ALL_CPUS) {
-			ret = -EINVAL;
-			break;
-		}
+		if (iter->cpu_file != RING_BUFFER_ALL_CPUS)
+			return -EINVAL;
 #endif
 		if (tr->allocated_snapshot)
 			ret = resize_buffer_duplicate_size(&tr->max_buffer,
@@ -7337,7 +7283,7 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 
 		ret = tracing_arm_snapshot_locked(tr);
 		if (ret)
-			break;
+			return ret;
 
 		/* Now, we're going to swap */
 		if (iter->cpu_file == RING_BUFFER_ALL_CPUS) {
@@ -7364,8 +7310,7 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 		*ppos += cnt;
 		ret = cnt;
 	}
-out:
-	mutex_unlock(&trace_types_lock);
+
 	return ret;
 }
 
@@ -7751,12 +7696,11 @@ void tracing_log_err(struct trace_array *tr,
 
 	len += sizeof(CMD_PREFIX) + 2 * sizeof("\n") + strlen(cmd) + 1;
 
-	mutex_lock(&tracing_err_log_lock);
+	guard(mutex)(&tracing_err_log_lock);
+
 	err = get_tracing_log_err(tr, len);
-	if (PTR_ERR(err) == -ENOMEM) {
-		mutex_unlock(&tracing_err_log_lock);
+	if (PTR_ERR(err) == -ENOMEM)
 		return;
-	}
 
 	snprintf(err->loc, TRACING_LOG_LOC_MAX, "%s: error: ", loc);
 	snprintf(err->cmd, len, "\n" CMD_PREFIX "%s\n", cmd);
@@ -7767,7 +7711,6 @@ void tracing_log_err(struct trace_array *tr,
 	err->info.ts = local_clock();
 
 	list_add_tail(&err->list, &tr->err_log);
-	mutex_unlock(&tracing_err_log_lock);
 }
 
 static void clear_tracing_err_log(struct trace_array *tr)
@@ -9511,20 +9454,17 @@ static int instance_mkdir(const char *name)
 	struct trace_array *tr;
 	int ret;
 
-	mutex_lock(&event_mutex);
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&event_mutex);
+	guard(mutex)(&trace_types_lock);
 
 	ret = -EEXIST;
 	if (trace_array_find(name))
-		goto out_unlock;
+		return -EEXIST;
 
 	tr = trace_array_create(name);
 
 	ret = PTR_ERR_OR_ZERO(tr);
 
-out_unlock:
-	mutex_unlock(&trace_types_lock);
-	mutex_unlock(&event_mutex);
 	return ret;
 }
 
@@ -9574,24 +9514,23 @@ struct trace_array *trace_array_get_by_name(const char *name, const char *system
 {
 	struct trace_array *tr;
 
-	mutex_lock(&event_mutex);
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&event_mutex);
+	guard(mutex)(&trace_types_lock);
 
 	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
-		if (tr->name && strcmp(tr->name, name) == 0)
-			goto out_unlock;
+		if (tr->name && strcmp(tr->name, name) == 0) {
+			tr->ref++;
+			return tr;
+		}
 	}
 
 	tr = trace_array_create_systems(name, systems, 0, 0);
 
 	if (IS_ERR(tr))
 		tr = NULL;
-out_unlock:
-	if (tr)
+	else
 		tr->ref++;
 
-	mutex_unlock(&trace_types_lock);
-	mutex_unlock(&event_mutex);
 	return tr;
 }
 EXPORT_SYMBOL_GPL(trace_array_get_by_name);
@@ -9642,48 +9581,36 @@ static int __remove_instance(struct trace_array *tr)
 int trace_array_destroy(struct trace_array *this_tr)
 {
 	struct trace_array *tr;
-	int ret;
 
 	if (!this_tr)
 		return -EINVAL;
 
-	mutex_lock(&event_mutex);
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&event_mutex);
+	guard(mutex)(&trace_types_lock);
 
-	ret = -ENODEV;
 
 	/* Making sure trace array exists before destroying it. */
 	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
-		if (tr == this_tr) {
-			ret = __remove_instance(tr);
-			break;
-		}
+		if (tr == this_tr)
+			return __remove_instance(tr);
 	}
 
-	mutex_unlock(&trace_types_lock);
-	mutex_unlock(&event_mutex);
-
-	return ret;
+	return -ENODEV;
 }
 EXPORT_SYMBOL_GPL(trace_array_destroy);
 
 static int instance_rmdir(const char *name)
 {
 	struct trace_array *tr;
-	int ret;
 
-	mutex_lock(&event_mutex);
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&event_mutex);
+	guard(mutex)(&trace_types_lock);
 
-	ret = -ENODEV;
 	tr = trace_array_find(name);
-	if (tr)
-		ret = __remove_instance(tr);
-
-	mutex_unlock(&trace_types_lock);
-	mutex_unlock(&event_mutex);
+	if (!tr)
+		return -ENODEV;
 
-	return ret;
+	return __remove_instance(tr);
 }
 
 static __init void create_trace_instances(struct dentry *d_tracer)
@@ -9696,19 +9623,16 @@ static __init void create_trace_instances(struct dentry *d_tracer)
 	if (MEM_FAIL(!trace_instance_dir, "Failed to create instances directory\n"))
 		return;
 
-	mutex_lock(&event_mutex);
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&event_mutex);
+	guard(mutex)(&trace_types_lock);
 
 	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
 		if (!tr->name)
 			continue;
 		if (MEM_FAIL(trace_array_create_dir(tr) < 0,
 			     "Failed to create instance directory\n"))
-			break;
+			return;
 	}
-
-	mutex_unlock(&trace_types_lock);
-	mutex_unlock(&event_mutex);
 }
 
 static void
@@ -9922,7 +9846,7 @@ static void trace_module_remove_evals(struct module *mod)
 	if (!mod->num_trace_evals)
 		return;
 
-	mutex_lock(&trace_eval_mutex);
+	guard(mutex)(&trace_eval_mutex);
 
 	map = trace_eval_maps;
 
@@ -9934,12 +9858,10 @@ static void trace_module_remove_evals(struct module *mod)
 		map = map->tail.next;
 	}
 	if (!map)
-		goto out;
+		return;
 
 	*last = trace_eval_jmp_to_tail(map)->tail.next;
 	kfree(map);
- out:
-	mutex_unlock(&trace_eval_mutex);
 }
 #else
 static inline void trace_module_remove_evals(struct module *mod) { }
-- 
2.45.2

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