[PATCH 06/20] pid: Implement PIDTYPE_TGID

From: Eric W. Biederman
Date: Mon Jul 23 2018 - 23:25:45 EST

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Everywhere except in the pid array we distinguish between a tasks pid and
a tasks tgid (thread group id). Even in the enumeration we want that
distinction sometimes so we have added __PIDTYPE_TGID. With leader_pid
we almost have an implementation of PIDTYPE_TGID in struct signal_struct.

Add PIDTYPE_TGID as a first class member of the pid_type enumeration and
into the pids array. Then remove the __PIDTYPE_TGID special case and the
leader_pid in signal_struct.

The net size increase is just an extra pointer added to struct pid and
an extra pair of pointers of an hlist_node added to task_struct.

The effect on code maintenance is the removal of a number of special
cases today and the potential to remove many more special cases as
PIDTYPE_TGID gets used to it's fullest. The long term potential
is allowing zombie thread group leaders to exit, which will remove
a lot more special cases in the code.

Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
arch/ia64/kernel/asm-offsets.c | 2 +-
arch/ia64/kernel/fsys.S | 4 ++--
arch/s390/kernel/perf_cpum_sf.c | 2 +-
fs/exec.c | 1 +
include/linux/pid.h | 3 +--
include/linux/sched.h | 4 ++--
include/linux/sched/signal.h | 5 ++---
init/init_task.c | 2 +-
kernel/events/core.c | 2 +-
kernel/exit.c | 1 +
kernel/fork.c | 3 ++-
kernel/pid.c | 2 --
kernel/time/itimer.c | 5 +++--
kernel/time/posix-cpu-timers.c | 2 +-
14 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/arch/ia64/kernel/asm-offsets.c b/arch/ia64/kernel/asm-offsets.c
index c1f8a57855af..00e8e2a1eb19 100644
--- a/arch/ia64/kernel/asm-offsets.c
+++ b/arch/ia64/kernel/asm-offsets.c
@@ -67,7 +67,7 @@ void foo(void)
DEFINE(IA64_SIGNAL_GROUP_STOP_COUNT_OFFSET,offsetof (struct signal_struct,
group_stop_count));
DEFINE(IA64_SIGNAL_SHARED_PENDING_OFFSET,offsetof (struct signal_struct, shared_pending));
- DEFINE(IA64_SIGNAL_LEADER_PID_OFFSET, offsetof (struct signal_struct, leader_pid));
+ DEFINE(IA64_SIGNAL_PIDS_TGID_OFFSET, offsetof (struct signal_struct, pids[PIDTYPE_TGID]));

BLANK();

diff --git a/arch/ia64/kernel/fsys.S b/arch/ia64/kernel/fsys.S
index e85ebdac678b..d80c99a5f55d 100644
--- a/arch/ia64/kernel/fsys.S
+++ b/arch/ia64/kernel/fsys.S
@@ -68,10 +68,10 @@ ENTRY(fsys_getpid)
add r9=TI_FLAGS+IA64_TASK_SIZE,r16
;;
ld4 r9=[r9]
- add r17=IA64_SIGNAL_LEADER_PID_OFFSET,r17
+ add r17=IA64_SIGNAL_PIDS_TGID_OFFSET,r17
;;
and r9=TIF_ALLWORK_MASK,r9
- ld8 r17=[r17] // r17 = current->signal->leader_pid
+ ld8 r17=[r17] // r17 = current->signal->pids[PIDTYPE_TGID]
;;
add r8=IA64_PID_LEVEL_OFFSET,r17
;;
diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index 0292d68e7dde..ca0b7ae894bb 100644
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -665,7 +665,7 @@ static void cpumsf_output_event_pid(struct perf_event *event,
goto out;

/* Update the process ID (see also kernel/events/core.c) */
- data->tid_entry.pid = cpumsf_pid_type(event, pid, __PIDTYPE_TGID);
+ data->tid_entry.pid = cpumsf_pid_type(event, pid, PIDTYPE_TGID);
data->tid_entry.tid = cpumsf_pid_type(event, pid, PIDTYPE_PID);

perf_output_sample(&handle, &header, data, event);
diff --git a/fs/exec.c b/fs/exec.c
index 2d4e0075bd24..79a11fbded7a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1146,6 +1146,7 @@ static int de_thread(struct task_struct *tsk)
*/
tsk->pid = leader->pid;
change_pid(tsk, PIDTYPE_PID, task_pid(leader));
+ transfer_pid(leader, tsk, PIDTYPE_TGID);
transfer_pid(leader, tsk, PIDTYPE_PGID);
transfer_pid(leader, tsk, PIDTYPE_SID);

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 3d4c504dcc8c..14a9a39da9c7 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -7,11 +7,10 @@
enum pid_type
{
PIDTYPE_PID,
+ PIDTYPE_TGID,
PIDTYPE_PGID,
PIDTYPE_SID,
PIDTYPE_MAX,
- /* only valid to __task_pid_nr_ns() */
- __PIDTYPE_TGID
};

/*
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 445bdf5b1f64..06b4e3bda93a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1275,12 +1275,12 @@ static inline pid_t task_session_vnr(struct task_struct *tsk)

static inline pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
{
- return __task_pid_nr_ns(tsk, __PIDTYPE_TGID, ns);
+ return __task_pid_nr_ns(tsk, PIDTYPE_TGID, ns);
}

static inline pid_t task_tgid_vnr(struct task_struct *tsk)
{
- return __task_pid_nr_ns(tsk, __PIDTYPE_TGID, NULL);
+ return __task_pid_nr_ns(tsk, PIDTYPE_TGID, NULL);
}

static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 2dcded16eb1e..ee30a5ba475f 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -147,7 +147,6 @@ struct signal_struct {
#endif

/* PID/PID hash table linkage. */
- struct pid *leader_pid;
struct pid *pids[PIDTYPE_MAX];

#ifdef CONFIG_NO_HZ_FULL
@@ -571,7 +570,7 @@ struct pid *task_pid_type(struct task_struct *task, enum pid_type type)

static inline struct pid *task_tgid(struct task_struct *task)
{
- return task->signal->leader_pid;
+ return task->signal->pids[PIDTYPE_TGID];
}

/*
@@ -607,7 +606,7 @@ static inline bool thread_group_leader(struct task_struct *p)
*/
static inline bool has_group_leader_pid(struct task_struct *p)
{
- return task_pid(p) == p->signal->leader_pid;
+ return task_pid(p) == task_tgid(p);
}

static inline
diff --git a/init/init_task.c b/init/init_task.c
index db12a61259f1..4f97846256d7 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -33,9 +33,9 @@ static struct signal_struct init_signals = {
},
#endif
INIT_CPU_TIMERS(init_signals)
- .leader_pid = &init_struct_pid,
.pids = {
[PIDTYPE_PID] = &init_struct_pid,
+ [PIDTYPE_TGID] = &init_struct_pid,
[PIDTYPE_PGID] = &init_struct_pid,
[PIDTYPE_SID] = &init_struct_pid,
},
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 80cca2b30c4f..9025b1796ca8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1334,7 +1334,7 @@ static u32 perf_event_pid_type(struct perf_event *event, struct task_struct *p,

static u32 perf_event_pid(struct perf_event *event, struct task_struct *p)
{
- return perf_event_pid_type(event, p, __PIDTYPE_TGID);
+ return perf_event_pid_type(event, p, PIDTYPE_TGID);
}

static u32 perf_event_tid(struct perf_event *event, struct task_struct *p)
diff --git a/kernel/exit.c b/kernel/exit.c
index 16432428fc6c..25582b442955 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -73,6 +73,7 @@ static void __unhash_process(struct task_struct *p, bool group_dead)
nr_threads--;
detach_pid(p, PIDTYPE_PID);
if (group_dead) {
+ detach_pid(p, PIDTYPE_TGID);
detach_pid(p, PIDTYPE_PGID);
detach_pid(p, PIDTYPE_SID);

diff --git a/kernel/fork.c b/kernel/fork.c
index d2952162399b..cc5be0d01ce6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1946,6 +1946,7 @@ static __latent_entropy struct task_struct *copy_process(

init_task_pid(p, PIDTYPE_PID, pid);
if (thread_group_leader(p)) {
+ init_task_pid(p, PIDTYPE_TGID, pid);
init_task_pid(p, PIDTYPE_PGID, task_pgrp(current));
init_task_pid(p, PIDTYPE_SID, task_session(current));

@@ -1954,7 +1955,6 @@ static __latent_entropy struct task_struct *copy_process(
p->signal->flags |= SIGNAL_UNKILLABLE;
}

- p->signal->leader_pid = pid;
p->signal->tty = tty_kref_get(current->signal->tty);
/*
* Inherit has_child_subreaper flag under the same
@@ -1965,6 +1965,7 @@ static __latent_entropy struct task_struct *copy_process(
p->real_parent->signal->is_child_subreaper;
list_add_tail(&p->sibling, &p->real_parent->children);
list_add_tail_rcu(&p->tasks, &init_task.tasks);
+ attach_pid(p, PIDTYPE_TGID);
attach_pid(p, PIDTYPE_PGID);
attach_pid(p, PIDTYPE_SID);
__this_cpu_inc(process_counts);
diff --git a/kernel/pid.c b/kernel/pid.c
index f8486d2e2346..de1cfc4f75a2 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -269,8 +269,6 @@ 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];
}

diff --git a/kernel/time/itimer.c b/kernel/time/itimer.c
index f26acef5d7b4..9a65713c8309 100644
--- a/kernel/time/itimer.c
+++ b/kernel/time/itimer.c
@@ -139,9 +139,10 @@ enum hrtimer_restart it_real_fn(struct hrtimer *timer)
{
struct signal_struct *sig =
container_of(timer, struct signal_struct, real_timer);
+ struct pid *leader_pid = sig->pids[PIDTYPE_TGID];

- trace_itimer_expire(ITIMER_REAL, sig->leader_pid, 0);
- kill_pid_info(SIGALRM, SEND_SIG_PRIV, sig->leader_pid);
+ trace_itimer_expire(ITIMER_REAL, leader_pid, 0);
+ kill_pid_info(SIGALRM, SEND_SIG_PRIV, leader_pid);

return HRTIMER_NORESTART;
}
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 5a6251ac6f7a..40e6fae46cec 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -895,7 +895,7 @@ static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,

trace_itimer_expire(signo == SIGPROF ?
ITIMER_PROF : ITIMER_VIRTUAL,
- tsk->signal->leader_pid, cur_time);
+ task_tgid(tsk), cur_time);
__group_send_sig_info(signo, SEND_SIG_PRIV, tsk);
}

--
2.17.1

Next message: Eric W. Biederman: "[PATCH 07/20] signal: Use PIDTYPE_TGID to clearly store where file signals will be sent"
Previous message: Eric W. Biederman: "[PATCH 05/20] pids: Move the pgrp and session pid pointers from task_struct to signal_struct"
In reply to: Eric W. Biederman: "[PATCH 05/20] pids: Move the pgrp and session pid pointers from task_struct to signal_struct"
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