ANDROID: Fix massive cpufreq_times memory leaks

Every time _cpu_up() is called for a CPU, idle_thread_get() is called
which then re-initializes a CPU's idle thread that was already
previously created and cached in a global variable in
smpboot.c. idle_thread_get() calls init_idle() which then calls
__sched_fork(). __sched_fork() is where cpufreq_task_times_init() is,
and cpufreq_task_times_init() allocates memory for the task struct's
time_in_state array.

Since idle_thread_get() reuses a task struct instance that was already
previously created, this means that every time it calls init_idle(),
cpufreq_task_times_init() allocates this array again and overwrites
the existing allocation that the idle thread already had.

This causes memory to be leaked every time a CPU is onlined. In order
to fix this, move allocation of time_in_state into _do_fork to avoid
allocating it at all for idle threads. The cpufreq times interface is
intended to be used for tracking userspace tasks, so we can safely
remove it from the kernel's idle threads without killing any
functionality.

But that's not all!

Task structs can be freed outside of release_task(), which creates
another memory leak because a task struct can be freed without having
its cpufreq times allocation freed. To fix this, free the cpufreq
times allocation at the same time that task struct allocations are
freed, in free_task().

Since free_task() can also be called in error paths of copy_process()
after dup_task_struct(), set time_in_state to NULL immediately after
calling dup_task_struct() to avoid possible double free.

Bug description and fix adapted from patch submitted by
Sultan Alsawaf <sultanxda@gmail.com> at
https://android-review.googlesource.com/c/kernel/msm/+/700134

Bug: 110044919
Test: Hikey960 builds, boots & reports /proc/<pid>/time_in_state
correctly
Change-Id: I12fe7611fc88eb7f6c39f8f7629ad27b6ec4722c
Signed-off-by: Connor O'Brien <connoro@google.com>

drivers/cpufreq/cpufreq_times.c

@@ -234,16 +234,19 @@ static int uid_time_in_state_seq_show(struct seq_file *m, void *v)
 
 void cpufreq_task_times_init(struct task_struct *p)
 {
-	void *temp;
 	unsigned long flags;
-	unsigned int max_state;
 
 	spin_lock_irqsave(&task_time_in_state_lock, flags);
 	p->time_in_state = NULL;
 	spin_unlock_irqrestore(&task_time_in_state_lock, flags);
 	p->max_state = 0;
+}
 
-	max_state = READ_ONCE(next_offset);
+void cpufreq_task_times_alloc(struct task_struct *p)
+{
+	void *temp;
+	unsigned long flags;
+	unsigned int max_state = READ_ONCE(next_offset);
 
 	/* We use one array to avoid multiple allocs per task */
 	temp = kcalloc(max_state, sizeof(p->time_in_state[0]), GFP_ATOMIC);

include/linux/cpufreq_times.h

@@ -22,6 +22,7 @@
 
 #ifdef CONFIG_CPU_FREQ_TIMES
 void cpufreq_task_times_init(struct task_struct *p);
+void cpufreq_task_times_alloc(struct task_struct *p);
 void cpufreq_task_times_exit(struct task_struct *p);
 int proc_time_in_state_show(struct seq_file *m, struct pid_namespace *ns,
 			    struct pid *pid, struct task_struct *p);
@@ -32,6 +33,7 @@ void cpufreq_task_times_remove_uids(uid_t uid_start, uid_t uid_end);
 int single_uid_time_in_state_open(struct inode *inode, struct file *file);
 #else
 static inline void cpufreq_task_times_init(struct task_struct *p) {}
+static inline void cpufreq_task_times_alloc(struct task_struct *p) {}
 static inline void cpufreq_task_times_exit(struct task_struct *p) {}
 static inline void cpufreq_acct_update_power(struct task_struct *p,
 					     u64 cputime) {}

kernel/exit.c

@@ -54,7 +54,6 @@
 #include <linux/writeback.h>
 #include <linux/shm.h>
 #include <linux/kcov.h>
-#include <linux/cpufreq_times.h>
 
 #include "sched/tune.h"
 
@@ -172,8 +171,6 @@ void release_task(struct task_struct *p)
 {
 	struct task_struct *leader;
 	int zap_leader;
-
-	cpufreq_task_times_exit(p);
 repeat:
 	/* don't need to get the RCU readlock here - the process is dead and
 	 * can't be modifying its own credentials. But shut RCU-lockdep up */

kernel/fork.c

@@ -77,6 +77,7 @@
 #include <linux/compiler.h>
 #include <linux/sysctl.h>
 #include <linux/kcov.h>
+#include <linux/cpufreq_times.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -339,6 +340,8 @@ void put_task_stack(struct task_struct *tsk)
 
 void free_task(struct task_struct *tsk)
 {
+	cpufreq_task_times_exit(tsk);
+
 #ifndef CONFIG_THREAD_INFO_IN_TASK
 	/*
 	 * The task is finally done with both the stack and thread_info,
@@ -1527,6 +1530,8 @@ static __latent_entropy struct task_struct *copy_process(
 	if (!p)
 		goto fork_out;
 
+	cpufreq_task_times_init(p);
+
 	ftrace_graph_init_task(p);
 
 	rt_mutex_init_task(p);
@@ -1963,6 +1968,8 @@ long _do_fork(unsigned long clone_flags,
 		struct completion vfork;
 		struct pid *pid;
 
+		cpufreq_task_times_alloc(p);
+
 		trace_sched_process_fork(current, p);
 
 		pid = get_task_pid(p, PIDTYPE_PID);

kernel/sched/core.c

@@ -2261,8 +2261,6 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 	memset(&p->se.statistics, 0, sizeof(p->se.statistics));
 #endif
 
-	cpufreq_task_times_init(p);
-
 	RB_CLEAR_NODE(&p->dl.rb_node);
 	init_dl_task_timer(&p->dl);
 	__dl_clear_params(p);