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

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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
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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;