linux-stable/kernel/taskstats.c
Lukas Bulwahn 92333baace taskstats: remove unneeded dead assignment
make clang-analyzer on x86_64 defconfig caught my attention with:

  kernel/taskstats.c:120:2: warning: Value stored to 'rc' is never read \
  [clang-analyzer-deadcode.DeadStores]
          rc = 0;
          ^

Commit d94a041519 ("taskstats: free skb, avoid returns in
send_cpu_listeners") made send_cpu_listeners() not return a value and
hence, the rc variable remained only to be used within the loop where
it is always assigned before read and it does not need any other
initialisation.

So, simply remove this unneeded dead initializing assignment.

As compilers will detect this unneeded assignment and optimize this anyway,
the resulting object code is identical before and after this change.

No functional change. No change to object code.

[akpm@linux-foundation.org: reduce scope of `rc']

Link: https://lkml.kernel.org/r/20220307093942.21310-1-lukas.bulwahn@gmail.com
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Tom Rix <trix@redhat.com>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-03-23 19:00:35 -07:00

699 lines
15 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/*
* taskstats.c - Export per-task statistics to userland
*
* Copyright (C) Shailabh Nagar, IBM Corp. 2006
* (C) Balbir Singh, IBM Corp. 2006
*/
#include <linux/kernel.h>
#include <linux/taskstats_kern.h>
#include <linux/tsacct_kern.h>
#include <linux/delayacct.h>
#include <linux/cpumask.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/cgroupstats.h>
#include <linux/cgroup.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pid_namespace.h>
#include <net/genetlink.h>
#include <linux/atomic.h>
#include <linux/sched/cputime.h>
/*
* Maximum length of a cpumask that can be specified in
* the TASKSTATS_CMD_ATTR_REGISTER/DEREGISTER_CPUMASK attribute
*/
#define TASKSTATS_CPUMASK_MAXLEN (100+6*NR_CPUS)
static DEFINE_PER_CPU(__u32, taskstats_seqnum);
static int family_registered;
struct kmem_cache *taskstats_cache;
static struct genl_family family;
static const struct nla_policy taskstats_cmd_get_policy[] = {
[TASKSTATS_CMD_ATTR_PID] = { .type = NLA_U32 },
[TASKSTATS_CMD_ATTR_TGID] = { .type = NLA_U32 },
[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK] = { .type = NLA_STRING },
[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK] = { .type = NLA_STRING },};
static const struct nla_policy cgroupstats_cmd_get_policy[] = {
[CGROUPSTATS_CMD_ATTR_FD] = { .type = NLA_U32 },
};
struct listener {
struct list_head list;
pid_t pid;
char valid;
};
struct listener_list {
struct rw_semaphore sem;
struct list_head list;
};
static DEFINE_PER_CPU(struct listener_list, listener_array);
enum actions {
REGISTER,
DEREGISTER,
CPU_DONT_CARE
};
static int prepare_reply(struct genl_info *info, u8 cmd, struct sk_buff **skbp,
size_t size)
{
struct sk_buff *skb;
void *reply;
/*
* If new attributes are added, please revisit this allocation
*/
skb = genlmsg_new(size, GFP_KERNEL);
if (!skb)
return -ENOMEM;
if (!info) {
int seq = this_cpu_inc_return(taskstats_seqnum) - 1;
reply = genlmsg_put(skb, 0, seq, &family, 0, cmd);
} else
reply = genlmsg_put_reply(skb, info, &family, 0, cmd);
if (reply == NULL) {
nlmsg_free(skb);
return -EINVAL;
}
*skbp = skb;
return 0;
}
/*
* Send taskstats data in @skb to listener with nl_pid @pid
*/
static int send_reply(struct sk_buff *skb, struct genl_info *info)
{
struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(skb));
void *reply = genlmsg_data(genlhdr);
genlmsg_end(skb, reply);
return genlmsg_reply(skb, info);
}
/*
* Send taskstats data in @skb to listeners registered for @cpu's exit data
*/
static void send_cpu_listeners(struct sk_buff *skb,
struct listener_list *listeners)
{
struct genlmsghdr *genlhdr = nlmsg_data(nlmsg_hdr(skb));
struct listener *s, *tmp;
struct sk_buff *skb_next, *skb_cur = skb;
void *reply = genlmsg_data(genlhdr);
int delcount = 0;
genlmsg_end(skb, reply);
down_read(&listeners->sem);
list_for_each_entry(s, &listeners->list, list) {
int rc;
skb_next = NULL;
if (!list_is_last(&s->list, &listeners->list)) {
skb_next = skb_clone(skb_cur, GFP_KERNEL);
if (!skb_next)
break;
}
rc = genlmsg_unicast(&init_net, skb_cur, s->pid);
if (rc == -ECONNREFUSED) {
s->valid = 0;
delcount++;
}
skb_cur = skb_next;
}
up_read(&listeners->sem);
if (skb_cur)
nlmsg_free(skb_cur);
if (!delcount)
return;
/* Delete invalidated entries */
down_write(&listeners->sem);
list_for_each_entry_safe(s, tmp, &listeners->list, list) {
if (!s->valid) {
list_del(&s->list);
kfree(s);
}
}
up_write(&listeners->sem);
}
static void fill_stats(struct user_namespace *user_ns,
struct pid_namespace *pid_ns,
struct task_struct *tsk, struct taskstats *stats)
{
memset(stats, 0, sizeof(*stats));
/*
* Each accounting subsystem adds calls to its functions to
* fill in relevant parts of struct taskstsats as follows
*
* per-task-foo(stats, tsk);
*/
delayacct_add_tsk(stats, tsk);
/* fill in basic acct fields */
stats->version = TASKSTATS_VERSION;
stats->nvcsw = tsk->nvcsw;
stats->nivcsw = tsk->nivcsw;
bacct_add_tsk(user_ns, pid_ns, stats, tsk);
/* fill in extended acct fields */
xacct_add_tsk(stats, tsk);
}
static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
{
struct task_struct *tsk;
tsk = find_get_task_by_vpid(pid);
if (!tsk)
return -ESRCH;
fill_stats(current_user_ns(), task_active_pid_ns(current), tsk, stats);
put_task_struct(tsk);
return 0;
}
static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
{
struct task_struct *tsk, *first;
unsigned long flags;
int rc = -ESRCH;
u64 delta, utime, stime;
u64 start_time;
/*
* Add additional stats from live tasks except zombie thread group
* leaders who are already counted with the dead tasks
*/
rcu_read_lock();
first = find_task_by_vpid(tgid);
if (!first || !lock_task_sighand(first, &flags))
goto out;
if (first->signal->stats)
memcpy(stats, first->signal->stats, sizeof(*stats));
else
memset(stats, 0, sizeof(*stats));
tsk = first;
start_time = ktime_get_ns();
do {
if (tsk->exit_state)
continue;
/*
* Accounting subsystem can call its functions here to
* fill in relevant parts of struct taskstsats as follows
*
* per-task-foo(stats, tsk);
*/
delayacct_add_tsk(stats, tsk);
/* calculate task elapsed time in nsec */
delta = start_time - tsk->start_time;
/* Convert to micro seconds */
do_div(delta, NSEC_PER_USEC);
stats->ac_etime += delta;
task_cputime(tsk, &utime, &stime);
stats->ac_utime += div_u64(utime, NSEC_PER_USEC);
stats->ac_stime += div_u64(stime, NSEC_PER_USEC);
stats->nvcsw += tsk->nvcsw;
stats->nivcsw += tsk->nivcsw;
} while_each_thread(first, tsk);
unlock_task_sighand(first, &flags);
rc = 0;
out:
rcu_read_unlock();
stats->version = TASKSTATS_VERSION;
/*
* Accounting subsystems can also add calls here to modify
* fields of taskstats.
*/
return rc;
}
static void fill_tgid_exit(struct task_struct *tsk)
{
unsigned long flags;
spin_lock_irqsave(&tsk->sighand->siglock, flags);
if (!tsk->signal->stats)
goto ret;
/*
* Each accounting subsystem calls its functions here to
* accumalate its per-task stats for tsk, into the per-tgid structure
*
* per-task-foo(tsk->signal->stats, tsk);
*/
delayacct_add_tsk(tsk->signal->stats, tsk);
ret:
spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
return;
}
static int add_del_listener(pid_t pid, const struct cpumask *mask, int isadd)
{
struct listener_list *listeners;
struct listener *s, *tmp, *s2;
unsigned int cpu;
int ret = 0;
if (!cpumask_subset(mask, cpu_possible_mask))
return -EINVAL;
if (current_user_ns() != &init_user_ns)
return -EINVAL;
if (task_active_pid_ns(current) != &init_pid_ns)
return -EINVAL;
if (isadd == REGISTER) {
for_each_cpu(cpu, mask) {
s = kmalloc_node(sizeof(struct listener),
GFP_KERNEL, cpu_to_node(cpu));
if (!s) {
ret = -ENOMEM;
goto cleanup;
}
s->pid = pid;
s->valid = 1;
listeners = &per_cpu(listener_array, cpu);
down_write(&listeners->sem);
list_for_each_entry(s2, &listeners->list, list) {
if (s2->pid == pid && s2->valid)
goto exists;
}
list_add(&s->list, &listeners->list);
s = NULL;
exists:
up_write(&listeners->sem);
kfree(s); /* nop if NULL */
}
return 0;
}
/* Deregister or cleanup */
cleanup:
for_each_cpu(cpu, mask) {
listeners = &per_cpu(listener_array, cpu);
down_write(&listeners->sem);
list_for_each_entry_safe(s, tmp, &listeners->list, list) {
if (s->pid == pid) {
list_del(&s->list);
kfree(s);
break;
}
}
up_write(&listeners->sem);
}
return ret;
}
static int parse(struct nlattr *na, struct cpumask *mask)
{
char *data;
int len;
int ret;
if (na == NULL)
return 1;
len = nla_len(na);
if (len > TASKSTATS_CPUMASK_MAXLEN)
return -E2BIG;
if (len < 1)
return -EINVAL;
data = kmalloc(len, GFP_KERNEL);
if (!data)
return -ENOMEM;
nla_strscpy(data, na, len);
ret = cpulist_parse(data, mask);
kfree(data);
return ret;
}
static struct taskstats *mk_reply(struct sk_buff *skb, int type, u32 pid)
{
struct nlattr *na, *ret;
int aggr;
aggr = (type == TASKSTATS_TYPE_PID)
? TASKSTATS_TYPE_AGGR_PID
: TASKSTATS_TYPE_AGGR_TGID;
na = nla_nest_start_noflag(skb, aggr);
if (!na)
goto err;
if (nla_put(skb, type, sizeof(pid), &pid) < 0) {
nla_nest_cancel(skb, na);
goto err;
}
ret = nla_reserve_64bit(skb, TASKSTATS_TYPE_STATS,
sizeof(struct taskstats), TASKSTATS_TYPE_NULL);
if (!ret) {
nla_nest_cancel(skb, na);
goto err;
}
nla_nest_end(skb, na);
return nla_data(ret);
err:
return NULL;
}
static int cgroupstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
{
int rc = 0;
struct sk_buff *rep_skb;
struct cgroupstats *stats;
struct nlattr *na;
size_t size;
u32 fd;
struct fd f;
na = info->attrs[CGROUPSTATS_CMD_ATTR_FD];
if (!na)
return -EINVAL;
fd = nla_get_u32(info->attrs[CGROUPSTATS_CMD_ATTR_FD]);
f = fdget(fd);
if (!f.file)
return 0;
size = nla_total_size(sizeof(struct cgroupstats));
rc = prepare_reply(info, CGROUPSTATS_CMD_NEW, &rep_skb,
size);
if (rc < 0)
goto err;
na = nla_reserve(rep_skb, CGROUPSTATS_TYPE_CGROUP_STATS,
sizeof(struct cgroupstats));
if (na == NULL) {
nlmsg_free(rep_skb);
rc = -EMSGSIZE;
goto err;
}
stats = nla_data(na);
memset(stats, 0, sizeof(*stats));
rc = cgroupstats_build(stats, f.file->f_path.dentry);
if (rc < 0) {
nlmsg_free(rep_skb);
goto err;
}
rc = send_reply(rep_skb, info);
err:
fdput(f);
return rc;
}
static int cmd_attr_register_cpumask(struct genl_info *info)
{
cpumask_var_t mask;
int rc;
if (!alloc_cpumask_var(&mask, GFP_KERNEL))
return -ENOMEM;
rc = parse(info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK], mask);
if (rc < 0)
goto out;
rc = add_del_listener(info->snd_portid, mask, REGISTER);
out:
free_cpumask_var(mask);
return rc;
}
static int cmd_attr_deregister_cpumask(struct genl_info *info)
{
cpumask_var_t mask;
int rc;
if (!alloc_cpumask_var(&mask, GFP_KERNEL))
return -ENOMEM;
rc = parse(info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK], mask);
if (rc < 0)
goto out;
rc = add_del_listener(info->snd_portid, mask, DEREGISTER);
out:
free_cpumask_var(mask);
return rc;
}
static size_t taskstats_packet_size(void)
{
size_t size;
size = nla_total_size(sizeof(u32)) +
nla_total_size_64bit(sizeof(struct taskstats)) +
nla_total_size(0);
return size;
}
static int cmd_attr_pid(struct genl_info *info)
{
struct taskstats *stats;
struct sk_buff *rep_skb;
size_t size;
u32 pid;
int rc;
size = taskstats_packet_size();
rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, size);
if (rc < 0)
return rc;
rc = -EINVAL;
pid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_PID]);
stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID, pid);
if (!stats)
goto err;
rc = fill_stats_for_pid(pid, stats);
if (rc < 0)
goto err;
return send_reply(rep_skb, info);
err:
nlmsg_free(rep_skb);
return rc;
}
static int cmd_attr_tgid(struct genl_info *info)
{
struct taskstats *stats;
struct sk_buff *rep_skb;
size_t size;
u32 tgid;
int rc;
size = taskstats_packet_size();
rc = prepare_reply(info, TASKSTATS_CMD_NEW, &rep_skb, size);
if (rc < 0)
return rc;
rc = -EINVAL;
tgid = nla_get_u32(info->attrs[TASKSTATS_CMD_ATTR_TGID]);
stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID, tgid);
if (!stats)
goto err;
rc = fill_stats_for_tgid(tgid, stats);
if (rc < 0)
goto err;
return send_reply(rep_skb, info);
err:
nlmsg_free(rep_skb);
return rc;
}
static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
{
if (info->attrs[TASKSTATS_CMD_ATTR_REGISTER_CPUMASK])
return cmd_attr_register_cpumask(info);
else if (info->attrs[TASKSTATS_CMD_ATTR_DEREGISTER_CPUMASK])
return cmd_attr_deregister_cpumask(info);
else if (info->attrs[TASKSTATS_CMD_ATTR_PID])
return cmd_attr_pid(info);
else if (info->attrs[TASKSTATS_CMD_ATTR_TGID])
return cmd_attr_tgid(info);
else
return -EINVAL;
}
static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
{
struct signal_struct *sig = tsk->signal;
struct taskstats *stats_new, *stats;
/* Pairs with smp_store_release() below. */
stats = smp_load_acquire(&sig->stats);
if (stats || thread_group_empty(tsk))
return stats;
/* No problem if kmem_cache_zalloc() fails */
stats_new = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
spin_lock_irq(&tsk->sighand->siglock);
stats = sig->stats;
if (!stats) {
/*
* Pairs with smp_store_release() above and order the
* kmem_cache_zalloc().
*/
smp_store_release(&sig->stats, stats_new);
stats = stats_new;
stats_new = NULL;
}
spin_unlock_irq(&tsk->sighand->siglock);
if (stats_new)
kmem_cache_free(taskstats_cache, stats_new);
return stats;
}
/* Send pid data out on exit */
void taskstats_exit(struct task_struct *tsk, int group_dead)
{
int rc;
struct listener_list *listeners;
struct taskstats *stats;
struct sk_buff *rep_skb;
size_t size;
int is_thread_group;
if (!family_registered)
return;
/*
* Size includes space for nested attributes
*/
size = taskstats_packet_size();
is_thread_group = !!taskstats_tgid_alloc(tsk);
if (is_thread_group) {
/* PID + STATS + TGID + STATS */
size = 2 * size;
/* fill the tsk->signal->stats structure */
fill_tgid_exit(tsk);
}
listeners = raw_cpu_ptr(&listener_array);
if (list_empty(&listeners->list))
return;
rc = prepare_reply(NULL, TASKSTATS_CMD_NEW, &rep_skb, size);
if (rc < 0)
return;
stats = mk_reply(rep_skb, TASKSTATS_TYPE_PID,
task_pid_nr_ns(tsk, &init_pid_ns));
if (!stats)
goto err;
fill_stats(&init_user_ns, &init_pid_ns, tsk, stats);
/*
* Doesn't matter if tsk is the leader or the last group member leaving
*/
if (!is_thread_group || !group_dead)
goto send;
stats = mk_reply(rep_skb, TASKSTATS_TYPE_TGID,
task_tgid_nr_ns(tsk, &init_pid_ns));
if (!stats)
goto err;
memcpy(stats, tsk->signal->stats, sizeof(*stats));
send:
send_cpu_listeners(rep_skb, listeners);
return;
err:
nlmsg_free(rep_skb);
}
static const struct genl_ops taskstats_ops[] = {
{
.cmd = TASKSTATS_CMD_GET,
.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
.doit = taskstats_user_cmd,
.policy = taskstats_cmd_get_policy,
.maxattr = ARRAY_SIZE(taskstats_cmd_get_policy) - 1,
.flags = GENL_ADMIN_PERM,
},
{
.cmd = CGROUPSTATS_CMD_GET,
.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
.doit = cgroupstats_user_cmd,
.policy = cgroupstats_cmd_get_policy,
.maxattr = ARRAY_SIZE(cgroupstats_cmd_get_policy) - 1,
},
};
static struct genl_family family __ro_after_init = {
.name = TASKSTATS_GENL_NAME,
.version = TASKSTATS_GENL_VERSION,
.module = THIS_MODULE,
.ops = taskstats_ops,
.n_ops = ARRAY_SIZE(taskstats_ops),
};
/* Needed early in initialization */
void __init taskstats_init_early(void)
{
unsigned int i;
taskstats_cache = KMEM_CACHE(taskstats, SLAB_PANIC);
for_each_possible_cpu(i) {
INIT_LIST_HEAD(&(per_cpu(listener_array, i).list));
init_rwsem(&(per_cpu(listener_array, i).sem));
}
}
static int __init taskstats_init(void)
{
int rc;
rc = genl_register_family(&family);
if (rc)
return rc;
family_registered = 1;
pr_info("registered taskstats version %d\n", TASKSTATS_GENL_VERSION);
return 0;
}
/*
* late initcall ensures initialization of statistics collection
* mechanisms precedes initialization of the taskstats interface
*/
late_initcall(taskstats_init);