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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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22
include/linux/sched.h
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@@ -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)