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Subject[PATCH 05/20] 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>
---
arch/ia64/kernel/asm-offsets.c | 2 +-
arch/ia64/kernel/fsys.S | 4 +--
fs/autofs/autofs_i.h | 1 +
include/linux/init_task.h | 9 -------
include/linux/pid.h | 8 +-----
include/linux/sched.h | 22 +++--------------
include/linux/sched/signal.h | 26 +++++++++++++++++---
init/init_task.c | 11 +++++----
kernel/fork.c | 23 +++++++++++++----
kernel/pid.c | 45 +++++++++++++++++-----------------
10 files changed, 78 insertions(+), 73 deletions(-)

diff --git a/arch/ia64/kernel/asm-offsets.c b/arch/ia64/kernel/asm-offsets.c
index f5433bb7f04a..c1f8a57855af 100644
--- a/arch/ia64/kernel/asm-offsets.c
+++ b/arch/ia64/kernel/asm-offsets.c
@@ -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));
diff --git a/arch/ia64/kernel/fsys.S b/arch/ia64/kernel/fsys.S
index eaf5a0d6f3e0..e85ebdac678b 100644
--- a/arch/ia64/kernel/fsys.S
+++ b/arch/ia64/kernel/fsys.S
@@ -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
diff --git a/fs/autofs/autofs_i.h b/fs/autofs/autofs_i.h
index 9400a9f6318a..502812289850 100644
--- a/fs/autofs/autofs_i.h
+++ b/fs/autofs/autofs_i.h
@@ -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>
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index a454b8aeb938..a7083a45a26c 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -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 */
diff --git a/include/linux/pid.h b/include/linux/pid.h
index 7633d55d9a24..3d4c504dcc8c 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -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
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a461ff89a3af..445bdf5b1f64 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index b95a272c1ab5..2dcded16eb1e 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -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;
diff --git a/init/init_task.c b/init/init_task.c
index 7914ffb8dc73..db12a61259f1 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -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
diff --git a/kernel/fork.c b/kernel/fork.c
index 9440d61b925c..d2952162399b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -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 @@ static __latent_entropy struct task_struct *copy_process(
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);
}

diff --git a/kernel/pid.c b/kernel/pid.c
index d0de2b59f86f..f8486d2e2346 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -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;
--
2.17.1
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