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pids: Move the pgrp and session pid pointers from task_struct to signal_struct 

To access these fields the code always has to go to group leader so
going to signal struct is no loss and is actually a fundamental simplification.

This saves a little bit of memory by only allocating the pid pointer array
once instead of once for every thread, and even better this removes a
few potential races caused by the fact that group_leader can be changed
by de_thread, while signal_struct can not.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2017-09-26 13:06:43 -05:00
parent 71dbc8a969
commit 2c4704756c
10 changed files with 78 additions and 73 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/ia64/kernel/asm-offsets.c
View File

@ -50,7 +50,7 @@ void foo(void)
DEFINE(IA64_TASK_BLOCKED_OFFSET,offsetof (struct task_struct, blocked));
DEFINE(IA64_TASK_CLEAR_CHILD_TID_OFFSET,offsetof (struct task_struct, clear_child_tid));
DEFINE(IA64_TASK_TGIDLINK_OFFSET, offsetof (struct task_struct, pids[PIDTYPE_PID].pid));
DEFINE(IA64_TASK_THREAD_PID_OFFSET,offsetof (struct task_struct, thread_pid));
DEFINE(IA64_PID_LEVEL_OFFSET, offsetof (struct pid, level));
DEFINE(IA64_PID_UPID_OFFSET, offsetof (struct pid, numbers[0]));
DEFINE(IA64_TASK_PENDING_OFFSET,offsetof (struct task_struct, pending));

4
arch/ia64/kernel/fsys.S
View File

@ -96,11 +96,11 @@ ENTRY(fsys_set_tid_address)
.altrp b6
.body
add r9=TI_FLAGS+IA64_TASK_SIZE,r16
add r17=IA64_TASK_TGIDLINK_OFFSET,r16
add r17=IA64_TASK_THREAD_PID_OFFSET,r16
;;
ld4 r9=[r9]
tnat.z p6,p7=r32 // check argument register for being NaT
ld8 r17=[r17] // r17 = current->pids[PIDTYPE_PID].pid
ld8 r17=[r17] // r17 = current->thread_pid
;;
and r9=TIF_ALLWORK_MASK,r9
add r8=IA64_PID_LEVEL_OFFSET,r17

1
fs/autofs/autofs_i.h
View File

@ -18,6 +18,7 @@
#include <linux/string.h>
#include <linux/wait.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/uaccess.h>

9
include/linux/init_task.h
View File

@ -46,15 +46,6 @@ extern struct cred init_cred;
#define INIT_CPU_TIMERS(s)
#endif
#define INIT_PID_LINK(type) \
{ \
.node = { \
.next = NULL, \
.pprev = NULL, \
}, \
.pid = &init_struct_pid, \
}
#define INIT_TASK_COMM "swapper"
/* Attach to the init_task data structure for proper alignment */

8
include/linux/pid.h
View File

@ -67,12 +67,6 @@ struct pid
extern struct pid init_struct_pid;
struct pid_link
{
struct hlist_node node;
struct pid *pid;
};
static inline struct pid *get_pid(struct pid *pid)
{
if (pid)
@ -177,7 +171,7 @@ pid_t pid_vnr(struct pid *pid);
do { \
if ((pid) != NULL) \
hlist_for_each_entry_rcu((task), \
&(pid)->tasks[type], pids[type].node) {
&(pid)->tasks[type], pid_links[type]) {
/*
* Both old and new leaders may be attached to

22
include/linux/sched.h
View File

@ -775,7 +775,8 @@ struct task_struct {
struct list_head ptrace_entry;
/* PID/PID hash table linkage. */
struct pid_link pids[PIDTYPE_MAX];
struct pid *thread_pid;
struct hlist_node pid_links[PIDTYPE_MAX];
struct list_head thread_group;
struct list_head thread_node;
@ -1199,22 +1200,7 @@ struct task_struct {
static inline struct pid *task_pid(struct task_struct *task)
{
return task->pids[PIDTYPE_PID].pid;
}
/*
* Without tasklist or RCU lock it is not safe to dereference
* the result of task_pgrp/task_session even if task == current,
* we can race with another thread doing sys_setsid/sys_setpgid.
*/
static inline struct pid *task_pgrp(struct task_struct *task)
{
return task->group_leader->pids[PIDTYPE_PGID].pid;
}
static inline struct pid *task_session(struct task_struct *task)
{
return task->group_leader->pids[PIDTYPE_SID].pid;
return task->thread_pid;
}
/*
@ -1263,7 +1249,7 @@ static inline pid_t task_tgid_nr(struct task_struct *tsk)
*/
static inline int pid_alive(const struct task_struct *p)
{
return p->pids[PIDTYPE_PID].pid != NULL;
return p->thread_pid != NULL;
}
static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)

26
include/linux/sched/signal.h
View File

@ -146,7 +146,9 @@ struct signal_struct {
#endif
/* PID/PID hash table linkage. */
struct pid *leader_pid;
struct pid *pids[PIDTYPE_MAX];
#ifdef CONFIG_NO_HZ_FULL
atomic_t tick_dep_mask;
@ -559,9 +561,12 @@ void walk_process_tree(struct task_struct *top, proc_visitor, void *);
static inline
struct pid *task_pid_type(struct task_struct *task, enum pid_type type)
{
if (type != PIDTYPE_PID)
task = task->group_leader;
return task->pids[type].pid;
struct pid *pid;
if (type == PIDTYPE_PID)
pid = task_pid(task);
else
pid = task->signal->pids[type];
return pid;
}
static inline struct pid *task_tgid(struct task_struct *task)
@ -569,6 +574,21 @@ static inline struct pid *task_tgid(struct task_struct *task)
return task->signal->leader_pid;
}
/*
* Without tasklist or RCU lock it is not safe to dereference
* the result of task_pgrp/task_session even if task == current,
* we can race with another thread doing sys_setsid/sys_setpgid.
*/
static inline struct pid *task_pgrp(struct task_struct *task)
{
return task->signal->pids[PIDTYPE_PGID];
}
static inline struct pid *task_session(struct task_struct *task)
{
return task->signal->pids[PIDTYPE_SID];
}
static inline int get_nr_threads(struct task_struct *tsk)
{
return tsk->signal->nr_threads;

11
init/init_task.c
View File

@ -34,6 +34,11 @@ static struct signal_struct init_signals = {
#endif
INIT_CPU_TIMERS(init_signals)
.leader_pid = &init_struct_pid,
.pids = {
[PIDTYPE_PID] = &init_struct_pid,
[PIDTYPE_PGID] = &init_struct_pid,
[PIDTYPE_SID] = &init_struct_pid,
},
INIT_PREV_CPUTIME(init_signals)
};
@ -112,11 +117,7 @@ struct task_struct init_task
INIT_CPU_TIMERS(init_task)
.pi_lock = __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock),
.timer_slack_ns = 50000, /* 50 usec default slack */
.pids = {
[PIDTYPE_PID] = INIT_PID_LINK(PIDTYPE_PID),
[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),
[PIDTYPE_SID] = INIT_PID_LINK(PIDTYPE_SID),
},
.thread_pid = &init_struct_pid,
.thread_group = LIST_HEAD_INIT(init_task.thread_group),
.thread_node = LIST_HEAD_INIT(init_signals.thread_head),
#ifdef CONFIG_AUDITSYSCALL

23
kernel/fork.c
View File

@ -1549,10 +1549,22 @@ static void posix_cpu_timers_init(struct task_struct *tsk)
static inline void posix_cpu_timers_init(struct task_struct *tsk) { }
#endif
static inline void init_task_pid_links(struct task_struct *task)
{
enum pid_type type;
for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
INIT_HLIST_NODE(&task->pid_links[type]);
}
}
static inline void
init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
{
task->pids[type].pid = pid;
if (type == PIDTYPE_PID)
task->thread_pid = pid;
else
task->signal->pids[type] = pid;
}
static inline void rcu_copy_process(struct task_struct *p)
@ -1928,6 +1940,7 @@ static __latent_entropy struct task_struct *copy_process(
goto bad_fork_cancel_cgroup;
}
init_task_pid_links(p);
if (likely(p->pid)) {
ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
@ -2036,13 +2049,13 @@ fork_out:
return ERR_PTR(retval);
}
static inline void init_idle_pids(struct pid_link *links)
static inline void init_idle_pids(struct task_struct *idle)
{
enum pid_type type;
for (type = PIDTYPE_PID; type < PIDTYPE_MAX; ++type) {
INIT_HLIST_NODE(&links[type].node); /* not really needed */
links[type].pid = &init_struct_pid;
INIT_HLIST_NODE(&idle->pid_links[type]); /* not really needed */
init_task_pid(idle, type, &init_struct_pid);
}
}
@ -2052,7 +2065,7 @@ struct task_struct *fork_idle(int cpu)
task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0,
cpu_to_node(cpu));
if (!IS_ERR(task)) {
init_idle_pids(task->pids);
init_idle_pids(task);
init_idle(task, cpu);
}

45
kernel/pid.c
View File

@ -265,27 +265,35 @@ struct pid *find_vpid(int nr)
}
EXPORT_SYMBOL_GPL(find_vpid);
static struct pid **task_pid_ptr(struct task_struct *task, enum pid_type type)
{
return (type == PIDTYPE_PID) ?
&task->thread_pid :
(type == __PIDTYPE_TGID) ?
&task->signal->leader_pid :
&task->signal->pids[type];
}
/*
* attach_pid() must be called with the tasklist_lock write-held.
*/
void attach_pid(struct task_struct *task, enum pid_type type)
{
struct pid_link *link = &task->pids[type];
hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
struct pid *pid = *task_pid_ptr(task, type);
hlist_add_head_rcu(&task->pid_links[type], &pid->tasks[type]);
}
static void __change_pid(struct task_struct *task, enum pid_type type,
struct pid *new)
{
struct pid_link *link;
struct pid **pid_ptr = task_pid_ptr(task, type);
struct pid *pid;
int tmp;
link = &task->pids[type];
pid = link->pid;
pid = *pid_ptr;
hlist_del_rcu(&link->node);
link->pid = new;
hlist_del_rcu(&task->pid_links[type]);
*pid_ptr = new;
for (tmp = PIDTYPE_MAX; --tmp >= 0; )
if (!hlist_empty(&pid->tasks[tmp]))
@ -310,8 +318,9 @@ void change_pid(struct task_struct *task, enum pid_type type,
void transfer_pid(struct task_struct *old, struct task_struct *new,
enum pid_type type)
{
new->pids[type].pid = old->pids[type].pid;
hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
if (type == PIDTYPE_PID)
new->thread_pid = old->thread_pid;
hlist_replace_rcu(&old->pid_links[type], &new->pid_links[type]);
}
struct task_struct *pid_task(struct pid *pid, enum pid_type type)
@ -322,7 +331,7 @@ struct task_struct *pid_task(struct pid *pid, enum pid_type type)
first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
lockdep_tasklist_lock_is_held());
if (first)
result = hlist_entry(first, struct task_struct, pids[(type)].node);
result = hlist_entry(first, struct task_struct, pid_links[(type)]);
}
return result;
}
@ -360,9 +369,7 @@ struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
{
struct pid *pid;
rcu_read_lock();
if (type != PIDTYPE_PID)
task = task->group_leader;
pid = get_pid(rcu_dereference(task->pids[type].pid));
pid = get_pid(rcu_dereference(*task_pid_ptr(task, type)));
rcu_read_unlock();
return pid;
}
@ -420,16 +427,8 @@ pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
rcu_read_lock();
if (!ns)
ns = task_active_pid_ns(current);
if (likely(pid_alive(task))) {
struct pid *pid;
if (type == PIDTYPE_PID)
pid = task_pid(task);
else if (type == __PIDTYPE_TGID)
pid = task_tgid(task);
else
pid = rcu_dereference(task->group_leader->pids[type].pid);
nr = pid_nr_ns(pid, ns);
}
if (likely(pid_alive(task)))
nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
rcu_read_unlock();
return nr;