[PATCH v4 0/3] tracing: Changes to saved_cmdlines

[PATCH v4 0/3] tracing: Changes to saved_cmdlines

[Steven Rostedt]

The first patch is to consolidate the map_cmdline_to_pid into the allocate
page for the saved_cmdlines structure.

The second patch removes some open coded saved_cmdlines logic in trace.c
into a helper function to make it a cleaner move.

The third patch simply moves code around. The goal is to keep all the
saved_cmdlines logic in one place. Currently it's in two files (trace.c and
trace_sched_switch.c). Since trace.c is awfully large, move all the code to
trace_sched_switch.c, as that's its only purpose today anyway.

Changes since v3: https://lore.kernel.org/linux-trace-kernel/20240216210047.584712062@goodmis.org/

- The map_cmdline_to_pid field was moved into the pages allocated of the
  structure and that replaced the kmalloc. But that field still had
  kfree() called on it in the freeing of the structure which caused
  a memory corruption.

Steven Rostedt (Google) (3):
      tracing: Have saved_cmdlines arrays all in one allocation
      tracing: Move open coded processing of tgid_map into helper function
      tracing: Move saved_cmdline code into trace_sched_switch.c

----
 kernel/trace/trace.c              | 509 +------------------------------------
 kernel/trace/trace.h              |  10 +
 kernel/trace/trace_sched_switch.c | 515 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 528 insertions(+), 506 deletions(-)

[PATCH v4 1/3] tracing: Have saved_cmdlines arrays all in one allocation

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The saved_cmdlines have three arrays for mapping PIDs to COMMs:

 - map_pid_to_cmdline[]
 - map_cmdline_to_pid[]
 - saved_cmdlines

The map_pid_to_cmdline[] is PID_MAX_DEFAULT in size and holds the index
into the other arrays. The map_cmdline_to_pid[] is a mapping back to the
full pid as it can be larger than PID_MAX_DEFAULT. And the
saved_cmdlines[] just holds the COMMs associated to the pids.

Currently the map_pid_to_cmdline[] and saved_cmdlines[] are allocated
together (in reality the saved_cmdlines is just in the memory of the
rounding of the allocation of the structure as it is always allocated in
powers of two). The map_cmdline_to_pid[] array is allocated separately.

Since the rounding to a power of two is rather large (it allows for 8000
elements in saved_cmdlines), also include the map_cmdline_to_pid[] array.
(This drops it to 6000 by default, which is still plenty for most use
cases). This saves even more memory as the map_cmdline_to_pid[] array
doesn't need to be allocated.

Link: https://lore.kernel.org/linux-trace-kernel/20240212174011.068211d9@gandalf.local.home/

Fixes: 44dc5c41b5b1 ("tracing: Fix wasted memory in saved_cmdlines logic")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v4: https://lore.kernel.org/linux-trace-kernel/20240216210150.379809261@goodmis.org

- Do not kfree() map_cmdline_to_pid now that it is included in the
  page allocations.

 kernel/trace/trace.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8198bfc54b58..52faa30e64ed 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2325,6 +2325,10 @@ struct saved_cmdlines_buffer {
 };
 static struct saved_cmdlines_buffer *savedcmd;
 
+/* Holds the size of a cmdline and pid element */
+#define SAVED_CMDLINE_MAP_ELEMENT_SIZE(s)			\
+	(TASK_COMM_LEN + sizeof((s)->map_cmdline_to_pid[0]))
+
 static inline char *get_saved_cmdlines(int idx)
 {
 	return &savedcmd->saved_cmdlines[idx * TASK_COMM_LEN];
@@ -2339,7 +2343,6 @@ static void free_saved_cmdlines_buffer(struct saved_cmdlines_buffer *s)
 {
 	int order = get_order(sizeof(*s) + s->cmdline_num * TASK_COMM_LEN);
 
-	kfree(s->map_cmdline_to_pid);
 	kmemleak_free(s);
 	free_pages((unsigned long)s, order);
 }
@@ -2352,7 +2355,7 @@ static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val)
 	int order;
 
 	/* Figure out how much is needed to hold the given number of cmdlines */
-	orig_size = sizeof(*s) + val * TASK_COMM_LEN;
+	orig_size = sizeof(*s) + val * SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
 	order = get_order(orig_size);
 	size = 1 << (order + PAGE_SHIFT);
 	page = alloc_pages(GFP_KERNEL, order);
@@ -2364,16 +2367,11 @@ static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val)
 	memset(s, 0, sizeof(*s));
 
 	/* Round up to actual allocation */
-	val = (size - sizeof(*s)) / TASK_COMM_LEN;
+	val = (size - sizeof(*s)) / SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
 	s->cmdline_num = val;
 
-	s->map_cmdline_to_pid = kmalloc_array(val,
-					      sizeof(*s->map_cmdline_to_pid),
-					      GFP_KERNEL);
-	if (!s->map_cmdline_to_pid) {
-		free_saved_cmdlines_buffer(s);
-		return NULL;
-	}
+	/* Place map_cmdline_to_pid array right after saved_cmdlines */
+	s->map_cmdline_to_pid = (unsigned *)&s->saved_cmdlines[val * TASK_COMM_LEN];
 
 	s->cmdline_idx = 0;
 	memset(&s->map_pid_to_cmdline, NO_CMDLINE_MAP,
-- 
2.43.0

[PATCH v4 2/3] tracing: Move open coded processing of tgid_map into helper function

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

In preparation of moving the saved_cmdlines logic out of trace.c and into
trace_sched_switch.c, replace the open coded manipulation of tgid_map in
set_tracer_flag() into a helper function trace_alloc_tgid_map() so that it
can be easily moved into trace_sched_switch.c without changing existing
functions in trace.c.

No functional changes.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 52faa30e64ed..06c593fc93d0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5432,10 +5432,31 @@ int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set)
 	return 0;
 }
 
-int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
+static int trace_alloc_tgid_map(void)
 {
 	int *map;
 
+	if (tgid_map)
+		return 0;
+
+	tgid_map_max = pid_max;
+	map = kvcalloc(tgid_map_max + 1, sizeof(*tgid_map),
+		       GFP_KERNEL);
+	if (!map)
+		return -ENOMEM;
+
+	/*
+	 * Pairs with smp_load_acquire() in
+	 * trace_find_tgid_ptr() to ensure that if it observes
+	 * the tgid_map we just allocated then it also observes
+	 * the corresponding tgid_map_max value.
+	 */
+	smp_store_release(&tgid_map, map);
+	return 0;
+}
+
+int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
+{
 	if ((mask == TRACE_ITER_RECORD_TGID) ||
 	    (mask == TRACE_ITER_RECORD_CMD))
 		lockdep_assert_held(&event_mutex);
@@ -5458,20 +5479,7 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
 		trace_event_enable_cmd_record(enabled);
 
 	if (mask == TRACE_ITER_RECORD_TGID) {
-		if (!tgid_map) {
-			tgid_map_max = pid_max;
-			map = kvcalloc(tgid_map_max + 1, sizeof(*tgid_map),
-				       GFP_KERNEL);
-
-			/*
-			 * Pairs with smp_load_acquire() in
-			 * trace_find_tgid_ptr() to ensure that if it observes
-			 * the tgid_map we just allocated then it also observes
-			 * the corresponding tgid_map_max value.
-			 */
-			smp_store_release(&tgid_map, map);
-		}
-		if (!tgid_map) {
+		if (trace_alloc_tgid_map() < 0) {
 			tr->trace_flags &= ~TRACE_ITER_RECORD_TGID;
 			return -ENOMEM;
 		}
-- 
2.43.0

[PATCH v4 3/3] tracing: Move saved_cmdline code into trace_sched_switch.c

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The code that handles saved_cmdlines is split between the trace.c file and
the trace_sched_switch.c. There's some history to this. The
trace_sched_switch.c was originally created to handle the sched_switch
tracer that was deprecated due to sched_switch trace event making it
obsolete. But that file did not get deleted as it had some code to help
with saved_cmdlines. But trace.c has grown tremendously since then. Just
move all the saved_cmdlines code into trace_sched_switch.c as that's the
only reason that file still exists, and trace.c has gotten too big.

No functional changes.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c              | 515 +-----------------------------
 kernel/trace/trace.h              |  10 +
 kernel/trace/trace_sched_switch.c | 515 ++++++++++++++++++++++++++++++
 3 files changed, 528 insertions(+), 512 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 06c593fc93d0..50fab999e72e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -39,7 +39,6 @@
 #include <linux/ctype.h>
 #include <linux/init.h>
 #include <linux/panic_notifier.h>
-#include <linux/kmemleak.h>
 #include <linux/poll.h>
 #include <linux/nmi.h>
 #include <linux/fs.h>
@@ -105,7 +104,7 @@ dummy_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
  * tracing is active, only save the comm when a trace event
  * occurred.
  */
-static DEFINE_PER_CPU(bool, trace_taskinfo_save);
+DEFINE_PER_CPU(bool, trace_taskinfo_save);
 
 /*
  * Kill all tracing for good (never come back).
@@ -2299,96 +2298,6 @@ void tracing_reset_all_online_cpus(void)
 	mutex_unlock(&trace_types_lock);
 }
 
-/*
- * The tgid_map array maps from pid to tgid; i.e. the value stored at index i
- * is the tgid last observed corresponding to pid=i.
- */
-static int *tgid_map;
-
-/* The maximum valid index into tgid_map. */
-static size_t tgid_map_max;
-
-#define SAVED_CMDLINES_DEFAULT 128
-#define NO_CMDLINE_MAP UINT_MAX
-/*
- * Preemption must be disabled before acquiring trace_cmdline_lock.
- * The various trace_arrays' max_lock must be acquired in a context
- * where interrupt is disabled.
- */
-static arch_spinlock_t trace_cmdline_lock = __ARCH_SPIN_LOCK_UNLOCKED;
-struct saved_cmdlines_buffer {
-	unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];
-	unsigned *map_cmdline_to_pid;
-	unsigned cmdline_num;
-	int cmdline_idx;
-	char saved_cmdlines[];
-};
-static struct saved_cmdlines_buffer *savedcmd;
-
-/* Holds the size of a cmdline and pid element */
-#define SAVED_CMDLINE_MAP_ELEMENT_SIZE(s)			\
-	(TASK_COMM_LEN + sizeof((s)->map_cmdline_to_pid[0]))
-
-static inline char *get_saved_cmdlines(int idx)
-{
-	return &savedcmd->saved_cmdlines[idx * TASK_COMM_LEN];
-}
-
-static inline void set_cmdline(int idx, const char *cmdline)
-{
-	strncpy(get_saved_cmdlines(idx), cmdline, TASK_COMM_LEN);
-}
-
-static void free_saved_cmdlines_buffer(struct saved_cmdlines_buffer *s)
-{
-	int order = get_order(sizeof(*s) + s->cmdline_num * TASK_COMM_LEN);
-
-	kmemleak_free(s);
-	free_pages((unsigned long)s, order);
-}
-
-static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val)
-{
-	struct saved_cmdlines_buffer *s;
-	struct page *page;
-	int orig_size, size;
-	int order;
-
-	/* Figure out how much is needed to hold the given number of cmdlines */
-	orig_size = sizeof(*s) + val * SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
-	order = get_order(orig_size);
-	size = 1 << (order + PAGE_SHIFT);
-	page = alloc_pages(GFP_KERNEL, order);
-	if (!page)
-		return NULL;
-
-	s = page_address(page);
-	kmemleak_alloc(s, size, 1, GFP_KERNEL);
-	memset(s, 0, sizeof(*s));
-
-	/* Round up to actual allocation */
-	val = (size - sizeof(*s)) / SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
-	s->cmdline_num = val;
-
-	/* Place map_cmdline_to_pid array right after saved_cmdlines */
-	s->map_cmdline_to_pid = (unsigned *)&s->saved_cmdlines[val * TASK_COMM_LEN];
-
-	s->cmdline_idx = 0;
-	memset(&s->map_pid_to_cmdline, NO_CMDLINE_MAP,
-	       sizeof(s->map_pid_to_cmdline));
-	memset(s->map_cmdline_to_pid, NO_CMDLINE_MAP,
-	       val * sizeof(*s->map_cmdline_to_pid));
-
-	return s;
-}
-
-static int trace_create_savedcmd(void)
-{
-	savedcmd = allocate_cmdlines_buffer(SAVED_CMDLINES_DEFAULT);
-
-	return savedcmd ? 0 : -ENOMEM;
-}
-
 int is_tracing_stopped(void)
 {
 	return global_trace.stop_count;
@@ -2481,201 +2390,6 @@ void tracing_stop(void)
 	return tracing_stop_tr(&global_trace);
 }
 
-static int trace_save_cmdline(struct task_struct *tsk)
-{
-	unsigned tpid, idx;
-
-	/* treat recording of idle task as a success */
-	if (!tsk->pid)
-		return 1;
-
-	tpid = tsk->pid & (PID_MAX_DEFAULT - 1);
-
-	/*
-	 * It's not the end of the world if we don't get
-	 * the lock, but we also don't want to spin
-	 * nor do we want to disable interrupts,
-	 * so if we miss here, then better luck next time.
-	 *
-	 * This is called within the scheduler and wake up, so interrupts
-	 * had better been disabled and run queue lock been held.
-	 */
-	lockdep_assert_preemption_disabled();
-	if (!arch_spin_trylock(&trace_cmdline_lock))
-		return 0;
-
-	idx = savedcmd->map_pid_to_cmdline[tpid];
-	if (idx == NO_CMDLINE_MAP) {
-		idx = (savedcmd->cmdline_idx + 1) % savedcmd->cmdline_num;
-
-		savedcmd->map_pid_to_cmdline[tpid] = idx;
-		savedcmd->cmdline_idx = idx;
-	}
-
-	savedcmd->map_cmdline_to_pid[idx] = tsk->pid;
-	set_cmdline(idx, tsk->comm);
-
-	arch_spin_unlock(&trace_cmdline_lock);
-
-	return 1;
-}
-
-static void __trace_find_cmdline(int pid, char comm[])
-{
-	unsigned map;
-	int tpid;
-
-	if (!pid) {
-		strcpy(comm, "<idle>");
-		return;
-	}
-
-	if (WARN_ON_ONCE(pid < 0)) {
-		strcpy(comm, "<XXX>");
-		return;
-	}
-
-	tpid = pid & (PID_MAX_DEFAULT - 1);
-	map = savedcmd->map_pid_to_cmdline[tpid];
-	if (map != NO_CMDLINE_MAP) {
-		tpid = savedcmd->map_cmdline_to_pid[map];
-		if (tpid == pid) {
-			strscpy(comm, get_saved_cmdlines(map), TASK_COMM_LEN);
-			return;
-		}
-	}
-	strcpy(comm, "<...>");
-}
-
-void trace_find_cmdline(int pid, char comm[])
-{
-	preempt_disable();
-	arch_spin_lock(&trace_cmdline_lock);
-
-	__trace_find_cmdline(pid, comm);
-
-	arch_spin_unlock(&trace_cmdline_lock);
-	preempt_enable();
-}
-
-static int *trace_find_tgid_ptr(int pid)
-{
-	/*
-	 * Pairs with the smp_store_release in set_tracer_flag() to ensure that
-	 * if we observe a non-NULL tgid_map then we also observe the correct
-	 * tgid_map_max.
-	 */
-	int *map = smp_load_acquire(&tgid_map);
-
-	if (unlikely(!map || pid > tgid_map_max))
-		return NULL;
-
-	return &map[pid];
-}
-
-int trace_find_tgid(int pid)
-{
-	int *ptr = trace_find_tgid_ptr(pid);
-
-	return ptr ? *ptr : 0;
-}
-
-static int trace_save_tgid(struct task_struct *tsk)
-{
-	int *ptr;
-
-	/* treat recording of idle task as a success */
-	if (!tsk->pid)
-		return 1;
-
-	ptr = trace_find_tgid_ptr(tsk->pid);
-	if (!ptr)
-		return 0;
-
-	*ptr = tsk->tgid;
-	return 1;
-}
-
-static bool tracing_record_taskinfo_skip(int flags)
-{
-	if (unlikely(!(flags & (TRACE_RECORD_CMDLINE | TRACE_RECORD_TGID))))
-		return true;
-	if (!__this_cpu_read(trace_taskinfo_save))
-		return true;
-	return false;
-}
-
-/**
- * tracing_record_taskinfo - record the task info of a task
- *
- * @task:  task to record
- * @flags: TRACE_RECORD_CMDLINE for recording comm
- *         TRACE_RECORD_TGID for recording tgid
- */
-void tracing_record_taskinfo(struct task_struct *task, int flags)
-{
-	bool done;
-
-	if (tracing_record_taskinfo_skip(flags))
-		return;
-
-	/*
-	 * Record as much task information as possible. If some fail, continue
-	 * to try to record the others.
-	 */
-	done = !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(task);
-	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(task);
-
-	/* If recording any information failed, retry again soon. */
-	if (!done)
-		return;
-
-	__this_cpu_write(trace_taskinfo_save, false);
-}
-
-/**
- * tracing_record_taskinfo_sched_switch - record task info for sched_switch
- *
- * @prev: previous task during sched_switch
- * @next: next task during sched_switch
- * @flags: TRACE_RECORD_CMDLINE for recording comm
- *         TRACE_RECORD_TGID for recording tgid
- */
-void tracing_record_taskinfo_sched_switch(struct task_struct *prev,
-					  struct task_struct *next, int flags)
-{
-	bool done;
-
-	if (tracing_record_taskinfo_skip(flags))
-		return;
-
-	/*
-	 * Record as much task information as possible. If some fail, continue
-	 * to try to record the others.
-	 */
-	done  = !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(prev);
-	done &= !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(next);
-	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(prev);
-	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(next);
-
-	/* If recording any information failed, retry again soon. */
-	if (!done)
-		return;
-
-	__this_cpu_write(trace_taskinfo_save, false);
-}
-
-/* Helpers to record a specific task information */
-void tracing_record_cmdline(struct task_struct *task)
-{
-	tracing_record_taskinfo(task, TRACE_RECORD_CMDLINE);
-}
-
-void tracing_record_tgid(struct task_struct *task)
-{
-	tracing_record_taskinfo(task, TRACE_RECORD_TGID);
-}
-
 /*
  * Several functions return TRACE_TYPE_PARTIAL_LINE if the trace_seq
  * overflowed, and TRACE_TYPE_HANDLED otherwise. This helper function
@@ -5432,29 +5146,6 @@ int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set)
 	return 0;
 }
 
-static int trace_alloc_tgid_map(void)
-{
-	int *map;
-
-	if (tgid_map)
-		return 0;
-
-	tgid_map_max = pid_max;
-	map = kvcalloc(tgid_map_max + 1, sizeof(*tgid_map),
-		       GFP_KERNEL);
-	if (!map)
-		return -ENOMEM;
-
-	/*
-	 * Pairs with smp_load_acquire() in
-	 * trace_find_tgid_ptr() to ensure that if it observes
-	 * the tgid_map we just allocated then it also observes
-	 * the corresponding tgid_map_max value.
-	 */
-	smp_store_release(&tgid_map, map);
-	return 0;
-}
-
 int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
 {
 	if ((mask == TRACE_ITER_RECORD_TGID) ||
@@ -5479,6 +5170,7 @@ int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
 		trace_event_enable_cmd_record(enabled);
 
 	if (mask == TRACE_ITER_RECORD_TGID) {
+
 		if (trace_alloc_tgid_map() < 0) {
 			tr->trace_flags &= ~TRACE_ITER_RECORD_TGID;
 			return -ENOMEM;
@@ -5924,207 +5616,6 @@ static const struct file_operations tracing_readme_fops = {
 	.llseek		= generic_file_llseek,
 };
 
-static void *saved_tgids_next(struct seq_file *m, void *v, loff_t *pos)
-{
-	int pid = ++(*pos);
-
-	return trace_find_tgid_ptr(pid);
-}
-
-static void *saved_tgids_start(struct seq_file *m, loff_t *pos)
-{
-	int pid = *pos;
-
-	return trace_find_tgid_ptr(pid);
-}
-
-static void saved_tgids_stop(struct seq_file *m, void *v)
-{
-}
-
-static int saved_tgids_show(struct seq_file *m, void *v)
-{
-	int *entry = (int *)v;
-	int pid = entry - tgid_map;
-	int tgid = *entry;
-
-	if (tgid == 0)
-		return SEQ_SKIP;
-
-	seq_printf(m, "%d %d\n", pid, tgid);
-	return 0;
-}
-
-static const struct seq_operations tracing_saved_tgids_seq_ops = {
-	.start		= saved_tgids_start,
-	.stop		= saved_tgids_stop,
-	.next		= saved_tgids_next,
-	.show		= saved_tgids_show,
-};
-
-static int tracing_saved_tgids_open(struct inode *inode, struct file *filp)
-{
-	int ret;
-
-	ret = tracing_check_open_get_tr(NULL);
-	if (ret)
-		return ret;
-
-	return seq_open(filp, &tracing_saved_tgids_seq_ops);
-}
-
-
-static const struct file_operations tracing_saved_tgids_fops = {
-	.open		= tracing_saved_tgids_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= seq_release,
-};
-
-static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
-{
-	unsigned int *ptr = v;
-
-	if (*pos || m->count)
-		ptr++;
-
-	(*pos)++;
-
-	for (; ptr < &savedcmd->map_cmdline_to_pid[savedcmd->cmdline_num];
-	     ptr++) {
-		if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
-			continue;
-
-		return ptr;
-	}
-
-	return NULL;
-}
-
-static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
-{
-	void *v;
-	loff_t l = 0;
-
-	preempt_disable();
-	arch_spin_lock(&trace_cmdline_lock);
-
-	v = &savedcmd->map_cmdline_to_pid[0];
-	while (l <= *pos) {
-		v = saved_cmdlines_next(m, v, &l);
-		if (!v)
-			return NULL;
-	}
-
-	return v;
-}
-
-static void saved_cmdlines_stop(struct seq_file *m, void *v)
-{
-	arch_spin_unlock(&trace_cmdline_lock);
-	preempt_enable();
-}
-
-static int saved_cmdlines_show(struct seq_file *m, void *v)
-{
-	char buf[TASK_COMM_LEN];
-	unsigned int *pid = v;
-
-	__trace_find_cmdline(*pid, buf);
-	seq_printf(m, "%d %s\n", *pid, buf);
-	return 0;
-}
-
-static const struct seq_operations tracing_saved_cmdlines_seq_ops = {
-	.start		= saved_cmdlines_start,
-	.next		= saved_cmdlines_next,
-	.stop		= saved_cmdlines_stop,
-	.show		= saved_cmdlines_show,
-};
-
-static int tracing_saved_cmdlines_open(struct inode *inode, struct file *filp)
-{
-	int ret;
-
-	ret = tracing_check_open_get_tr(NULL);
-	if (ret)
-		return ret;
-
-	return seq_open(filp, &tracing_saved_cmdlines_seq_ops);
-}
-
-static const struct file_operations tracing_saved_cmdlines_fops = {
-	.open		= tracing_saved_cmdlines_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= seq_release,
-};
-
-static ssize_t
-tracing_saved_cmdlines_size_read(struct file *filp, char __user *ubuf,
-				 size_t cnt, loff_t *ppos)
-{
-	char buf[64];
-	int r;
-
-	preempt_disable();
-	arch_spin_lock(&trace_cmdline_lock);
-	r = scnprintf(buf, sizeof(buf), "%u\n", savedcmd->cmdline_num);
-	arch_spin_unlock(&trace_cmdline_lock);
-	preempt_enable();
-
-	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
-}
-
-static int tracing_resize_saved_cmdlines(unsigned int val)
-{
-	struct saved_cmdlines_buffer *s, *savedcmd_temp;
-
-	s = allocate_cmdlines_buffer(val);
-	if (!s)
-		return -ENOMEM;
-
-	preempt_disable();
-	arch_spin_lock(&trace_cmdline_lock);
-	savedcmd_temp = savedcmd;
-	savedcmd = s;
-	arch_spin_unlock(&trace_cmdline_lock);
-	preempt_enable();
-	free_saved_cmdlines_buffer(savedcmd_temp);
-
-	return 0;
-}
-
-static ssize_t
-tracing_saved_cmdlines_size_write(struct file *filp, const char __user *ubuf,
-				  size_t cnt, loff_t *ppos)
-{
-	unsigned long val;
-	int ret;
-
-	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
-	if (ret)
-		return ret;
-
-	/* must have at least 1 entry or less than PID_MAX_DEFAULT */
-	if (!val || val > PID_MAX_DEFAULT)
-		return -EINVAL;
-
-	ret = tracing_resize_saved_cmdlines((unsigned int)val);
-	if (ret < 0)
-		return ret;
-
-	*ppos += cnt;
-
-	return cnt;
-}
-
-static const struct file_operations tracing_saved_cmdlines_size_fops = {
-	.open		= tracing_open_generic,
-	.read		= tracing_saved_cmdlines_size_read,
-	.write		= tracing_saved_cmdlines_size_write,
-};
-
 #ifdef CONFIG_TRACE_EVAL_MAP_FILE
 static union trace_eval_map_item *
 update_eval_map(union trace_eval_map_item *ptr)
@@ -10693,7 +10184,7 @@ __init static int tracer_alloc_buffers(void)
 out_free_pipe_cpumask:
 	free_cpumask_var(global_trace.pipe_cpumask);
 out_free_savedcmd:
-	free_saved_cmdlines_buffer(savedcmd);
+	trace_free_saved_cmdlines_buffer();
 out_free_temp_buffer:
 	ring_buffer_free(temp_buffer);
 out_rm_hp_state:
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 00f873910c5d..e4f0714d7a49 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1375,6 +1375,16 @@ static inline void trace_buffer_unlock_commit(struct trace_array *tr,
 	trace_buffer_unlock_commit_regs(tr, buffer, event, trace_ctx, NULL);
 }
 
+DECLARE_PER_CPU(bool, trace_taskinfo_save);
+int trace_save_cmdline(struct task_struct *tsk);
+int trace_create_savedcmd(void);
+int trace_alloc_tgid_map(void);
+void trace_free_saved_cmdlines_buffer(void);
+
+extern const struct file_operations tracing_saved_cmdlines_fops;
+extern const struct file_operations tracing_saved_tgids_fops;
+extern const struct file_operations tracing_saved_cmdlines_size_fops;
+
 DECLARE_PER_CPU(struct ring_buffer_event *, trace_buffered_event);
 DECLARE_PER_CPU(int, trace_buffered_event_cnt);
 void trace_buffered_event_disable(void);
diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index c9ffdcfe622e..8a407adb0e1c 100644
--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -8,6 +8,7 @@
 #include <linux/module.h>
 #include <linux/kallsyms.h>
 #include <linux/uaccess.h>
+#include <linux/kmemleak.h>
 #include <linux/ftrace.h>
 #include <trace/events/sched.h>
 
@@ -148,3 +149,517 @@ void tracing_stop_tgid_record(void)
 {
 	tracing_stop_sched_switch(RECORD_TGID);
 }
+
+/*
+ * The tgid_map array maps from pid to tgid; i.e. the value stored at index i
+ * is the tgid last observed corresponding to pid=i.
+ */
+static int *tgid_map;
+
+/* The maximum valid index into tgid_map. */
+static size_t tgid_map_max;
+
+#define SAVED_CMDLINES_DEFAULT 128
+#define NO_CMDLINE_MAP UINT_MAX
+/*
+ * Preemption must be disabled before acquiring trace_cmdline_lock.
+ * The various trace_arrays' max_lock must be acquired in a context
+ * where interrupt is disabled.
+ */
+static arch_spinlock_t trace_cmdline_lock = __ARCH_SPIN_LOCK_UNLOCKED;
+struct saved_cmdlines_buffer {
+	unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];
+	unsigned *map_cmdline_to_pid;
+	unsigned cmdline_num;
+	int cmdline_idx;
+	char saved_cmdlines[];
+};
+static struct saved_cmdlines_buffer *savedcmd;
+
+/* Holds the size of a cmdline and pid element */
+#define SAVED_CMDLINE_MAP_ELEMENT_SIZE(s)			\
+	(TASK_COMM_LEN + sizeof((s)->map_cmdline_to_pid[0]))
+
+static inline char *get_saved_cmdlines(int idx)
+{
+	return &savedcmd->saved_cmdlines[idx * TASK_COMM_LEN];
+}
+
+static inline void set_cmdline(int idx, const char *cmdline)
+{
+	strncpy(get_saved_cmdlines(idx), cmdline, TASK_COMM_LEN);
+}
+
+static void free_saved_cmdlines_buffer(struct saved_cmdlines_buffer *s)
+{
+	int order = get_order(sizeof(*s) + s->cmdline_num * TASK_COMM_LEN);
+
+	kmemleak_free(s);
+	free_pages((unsigned long)s, order);
+}
+
+static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val)
+{
+	struct saved_cmdlines_buffer *s;
+	struct page *page;
+	int orig_size, size;
+	int order;
+
+	/* Figure out how much is needed to hold the given number of cmdlines */
+	orig_size = sizeof(*s) + val * SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
+	order = get_order(orig_size);
+	size = 1 << (order + PAGE_SHIFT);
+	page = alloc_pages(GFP_KERNEL, order);
+	if (!page)
+		return NULL;
+
+	s = page_address(page);
+	kmemleak_alloc(s, size, 1, GFP_KERNEL);
+	memset(s, 0, sizeof(*s));
+
+	/* Round up to actual allocation */
+	val = (size - sizeof(*s)) / SAVED_CMDLINE_MAP_ELEMENT_SIZE(s);
+	s->cmdline_num = val;
+
+	/* Place map_cmdline_to_pid array right after saved_cmdlines */
+	s->map_cmdline_to_pid = (unsigned *)&s->saved_cmdlines[val * TASK_COMM_LEN];
+
+	s->cmdline_idx = 0;
+	memset(&s->map_pid_to_cmdline, NO_CMDLINE_MAP,
+	       sizeof(s->map_pid_to_cmdline));
+	memset(s->map_cmdline_to_pid, NO_CMDLINE_MAP,
+	       val * sizeof(*s->map_cmdline_to_pid));
+
+	return s;
+}
+
+int trace_create_savedcmd(void)
+{
+	savedcmd = allocate_cmdlines_buffer(SAVED_CMDLINES_DEFAULT);
+
+	return savedcmd ? 0 : -ENOMEM;
+}
+
+int trace_save_cmdline(struct task_struct *tsk)
+{
+	unsigned tpid, idx;
+
+	/* treat recording of idle task as a success */
+	if (!tsk->pid)
+		return 1;
+
+	tpid = tsk->pid & (PID_MAX_DEFAULT - 1);
+
+	/*
+	 * It's not the end of the world if we don't get
+	 * the lock, but we also don't want to spin
+	 * nor do we want to disable interrupts,
+	 * so if we miss here, then better luck next time.
+	 *
+	 * This is called within the scheduler and wake up, so interrupts
+	 * had better been disabled and run queue lock been held.
+	 */
+	lockdep_assert_preemption_disabled();
+	if (!arch_spin_trylock(&trace_cmdline_lock))
+		return 0;
+
+	idx = savedcmd->map_pid_to_cmdline[tpid];
+	if (idx == NO_CMDLINE_MAP) {
+		idx = (savedcmd->cmdline_idx + 1) % savedcmd->cmdline_num;
+
+		savedcmd->map_pid_to_cmdline[tpid] = idx;
+		savedcmd->cmdline_idx = idx;
+	}
+
+	savedcmd->map_cmdline_to_pid[idx] = tsk->pid;
+	set_cmdline(idx, tsk->comm);
+
+	arch_spin_unlock(&trace_cmdline_lock);
+
+	return 1;
+}
+
+static void __trace_find_cmdline(int pid, char comm[])
+{
+	unsigned map;
+	int tpid;
+
+	if (!pid) {
+		strcpy(comm, "<idle>");
+		return;
+	}
+
+	if (WARN_ON_ONCE(pid < 0)) {
+		strcpy(comm, "<XXX>");
+		return;
+	}
+
+	tpid = pid & (PID_MAX_DEFAULT - 1);
+	map = savedcmd->map_pid_to_cmdline[tpid];
+	if (map != NO_CMDLINE_MAP) {
+		tpid = savedcmd->map_cmdline_to_pid[map];
+		if (tpid == pid) {
+			strscpy(comm, get_saved_cmdlines(map), TASK_COMM_LEN);
+			return;
+		}
+	}
+	strcpy(comm, "<...>");
+}
+
+void trace_find_cmdline(int pid, char comm[])
+{
+	preempt_disable();
+	arch_spin_lock(&trace_cmdline_lock);
+
+	__trace_find_cmdline(pid, comm);
+
+	arch_spin_unlock(&trace_cmdline_lock);
+	preempt_enable();
+}
+
+static int *trace_find_tgid_ptr(int pid)
+{
+	/*
+	 * Pairs with the smp_store_release in set_tracer_flag() to ensure that
+	 * if we observe a non-NULL tgid_map then we also observe the correct
+	 * tgid_map_max.
+	 */
+	int *map = smp_load_acquire(&tgid_map);
+
+	if (unlikely(!map || pid > tgid_map_max))
+		return NULL;
+
+	return &map[pid];
+}
+
+int trace_find_tgid(int pid)
+{
+	int *ptr = trace_find_tgid_ptr(pid);
+
+	return ptr ? *ptr : 0;
+}
+
+static int trace_save_tgid(struct task_struct *tsk)
+{
+	int *ptr;
+
+	/* treat recording of idle task as a success */
+	if (!tsk->pid)
+		return 1;
+
+	ptr = trace_find_tgid_ptr(tsk->pid);
+	if (!ptr)
+		return 0;
+
+	*ptr = tsk->tgid;
+	return 1;
+}
+
+static bool tracing_record_taskinfo_skip(int flags)
+{
+	if (unlikely(!(flags & (TRACE_RECORD_CMDLINE | TRACE_RECORD_TGID))))
+		return true;
+	if (!__this_cpu_read(trace_taskinfo_save))
+		return true;
+	return false;
+}
+
+/**
+ * tracing_record_taskinfo - record the task info of a task
+ *
+ * @task:  task to record
+ * @flags: TRACE_RECORD_CMDLINE for recording comm
+ *         TRACE_RECORD_TGID for recording tgid
+ */
+void tracing_record_taskinfo(struct task_struct *task, int flags)
+{
+	bool done;
+
+	if (tracing_record_taskinfo_skip(flags))
+		return;
+
+	/*
+	 * Record as much task information as possible. If some fail, continue
+	 * to try to record the others.
+	 */
+	done = !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(task);
+	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(task);
+
+	/* If recording any information failed, retry again soon. */
+	if (!done)
+		return;
+
+	__this_cpu_write(trace_taskinfo_save, false);
+}
+
+/**
+ * tracing_record_taskinfo_sched_switch - record task info for sched_switch
+ *
+ * @prev: previous task during sched_switch
+ * @next: next task during sched_switch
+ * @flags: TRACE_RECORD_CMDLINE for recording comm
+ *         TRACE_RECORD_TGID for recording tgid
+ */
+void tracing_record_taskinfo_sched_switch(struct task_struct *prev,
+					  struct task_struct *next, int flags)
+{
+	bool done;
+
+	if (tracing_record_taskinfo_skip(flags))
+		return;
+
+	/*
+	 * Record as much task information as possible. If some fail, continue
+	 * to try to record the others.
+	 */
+	done  = !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(prev);
+	done &= !(flags & TRACE_RECORD_CMDLINE) || trace_save_cmdline(next);
+	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(prev);
+	done &= !(flags & TRACE_RECORD_TGID) || trace_save_tgid(next);
+
+	/* If recording any information failed, retry again soon. */
+	if (!done)
+		return;
+
+	__this_cpu_write(trace_taskinfo_save, false);
+}
+
+/* Helpers to record a specific task information */
+void tracing_record_cmdline(struct task_struct *task)
+{
+	tracing_record_taskinfo(task, TRACE_RECORD_CMDLINE);
+}
+
+void tracing_record_tgid(struct task_struct *task)
+{
+	tracing_record_taskinfo(task, TRACE_RECORD_TGID);
+}
+
+int trace_alloc_tgid_map(void)
+{
+	int *map;
+
+	if (tgid_map)
+		return 0;
+
+	tgid_map_max = pid_max;
+	map = kvcalloc(tgid_map_max + 1, sizeof(*tgid_map),
+		       GFP_KERNEL);
+	if (!map)
+		return -ENOMEM;
+
+	/*
+	 * Pairs with smp_load_acquire() in
+	 * trace_find_tgid_ptr() to ensure that if it observes
+	 * the tgid_map we just allocated then it also observes
+	 * the corresponding tgid_map_max value.
+	 */
+	smp_store_release(&tgid_map, map);
+	return 0;
+}
+
+static void *saved_tgids_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	int pid = ++(*pos);
+
+	return trace_find_tgid_ptr(pid);
+}
+
+static void *saved_tgids_start(struct seq_file *m, loff_t *pos)
+{
+	int pid = *pos;
+
+	return trace_find_tgid_ptr(pid);
+}
+
+static void saved_tgids_stop(struct seq_file *m, void *v)
+{
+}
+
+static int saved_tgids_show(struct seq_file *m, void *v)
+{
+	int *entry = (int *)v;
+	int pid = entry - tgid_map;
+	int tgid = *entry;
+
+	if (tgid == 0)
+		return SEQ_SKIP;
+
+	seq_printf(m, "%d %d\n", pid, tgid);
+	return 0;
+}
+
+static const struct seq_operations tracing_saved_tgids_seq_ops = {
+	.start		= saved_tgids_start,
+	.stop		= saved_tgids_stop,
+	.next		= saved_tgids_next,
+	.show		= saved_tgids_show,
+};
+
+static int tracing_saved_tgids_open(struct inode *inode, struct file *filp)
+{
+	int ret;
+
+	ret = tracing_check_open_get_tr(NULL);
+	if (ret)
+		return ret;
+
+	return seq_open(filp, &tracing_saved_tgids_seq_ops);
+}
+
+
+const struct file_operations tracing_saved_tgids_fops = {
+	.open		= tracing_saved_tgids_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	unsigned int *ptr = v;
+
+	if (*pos || m->count)
+		ptr++;
+
+	(*pos)++;
+
+	for (; ptr < &savedcmd->map_cmdline_to_pid[savedcmd->cmdline_num];
+	     ptr++) {
+		if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
+			continue;
+
+		return ptr;
+	}
+
+	return NULL;
+}
+
+static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
+{
+	void *v;
+	loff_t l = 0;
+
+	preempt_disable();
+	arch_spin_lock(&trace_cmdline_lock);
+
+	v = &savedcmd->map_cmdline_to_pid[0];
+	while (l <= *pos) {
+		v = saved_cmdlines_next(m, v, &l);
+		if (!v)
+			return NULL;
+	}
+
+	return v;
+}
+
+static void saved_cmdlines_stop(struct seq_file *m, void *v)
+{
+	arch_spin_unlock(&trace_cmdline_lock);
+	preempt_enable();
+}
+
+static int saved_cmdlines_show(struct seq_file *m, void *v)
+{
+	char buf[TASK_COMM_LEN];
+	unsigned int *pid = v;
+
+	__trace_find_cmdline(*pid, buf);
+	seq_printf(m, "%d %s\n", *pid, buf);
+	return 0;
+}
+
+static const struct seq_operations tracing_saved_cmdlines_seq_ops = {
+	.start		= saved_cmdlines_start,
+	.next		= saved_cmdlines_next,
+	.stop		= saved_cmdlines_stop,
+	.show		= saved_cmdlines_show,
+};
+
+static int tracing_saved_cmdlines_open(struct inode *inode, struct file *filp)
+{
+	int ret;
+
+	ret = tracing_check_open_get_tr(NULL);
+	if (ret)
+		return ret;
+
+	return seq_open(filp, &tracing_saved_cmdlines_seq_ops);
+}
+
+const struct file_operations tracing_saved_cmdlines_fops = {
+	.open		= tracing_saved_cmdlines_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static ssize_t
+tracing_saved_cmdlines_size_read(struct file *filp, char __user *ubuf,
+				 size_t cnt, loff_t *ppos)
+{
+	char buf[64];
+	int r;
+
+	preempt_disable();
+	arch_spin_lock(&trace_cmdline_lock);
+	r = scnprintf(buf, sizeof(buf), "%u\n", savedcmd->cmdline_num);
+	arch_spin_unlock(&trace_cmdline_lock);
+	preempt_enable();
+
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+void trace_free_saved_cmdlines_buffer(void)
+{
+	free_saved_cmdlines_buffer(savedcmd);
+}
+
+static int tracing_resize_saved_cmdlines(unsigned int val)
+{
+	struct saved_cmdlines_buffer *s, *savedcmd_temp;
+
+	s = allocate_cmdlines_buffer(val);
+	if (!s)
+		return -ENOMEM;
+
+	preempt_disable();
+	arch_spin_lock(&trace_cmdline_lock);
+	savedcmd_temp = savedcmd;
+	savedcmd = s;
+	arch_spin_unlock(&trace_cmdline_lock);
+	preempt_enable();
+	free_saved_cmdlines_buffer(savedcmd_temp);
+
+	return 0;
+}
+
+static ssize_t
+tracing_saved_cmdlines_size_write(struct file *filp, const char __user *ubuf,
+				  size_t cnt, loff_t *ppos)
+{
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+	if (ret)
+		return ret;
+
+	/* must have at least 1 entry or less than PID_MAX_DEFAULT */
+	if (!val || val > PID_MAX_DEFAULT)
+		return -EINVAL;
+
+	ret = tracing_resize_saved_cmdlines((unsigned int)val);
+	if (ret < 0)
+		return ret;
+
+	*ppos += cnt;
+
+	return cnt;
+}
+
+const struct file_operations tracing_saved_cmdlines_size_fops = {
+	.open		= tracing_open_generic,
+	.read		= tracing_saved_cmdlines_size_read,
+	.write		= tracing_saved_cmdlines_size_write,
+};
-- 
2.43.0