* [PATCH v4 0/2] prctl: make PR_SET_CHILD_SUBREAPER deterministic
@ 2017-01-30 15:06 Pavel Tikhomirov
2017-01-30 15:06 ` [PATCH 1/2] introduce the walk_process_tree() helper Pavel Tikhomirov
2017-01-30 15:06 ` [PATCH v4 2/2] prctl: propagate has_child_subreaper flag to every descendant Pavel Tikhomirov
0 siblings, 2 replies; 6+ messages in thread
From: Pavel Tikhomirov @ 2017-01-30 15:06 UTC (permalink / raw)
To: Ingo Molnar
Cc: Peter Zijlstra, Andrew Morton, Cyrill Gorcunov, John Stultz,
Thomas Gleixner, Oleg Nesterov, Nicolas Pitre, Michal Hocko,
Stanislav Kinsburskiy, Mateusz Guzik, linux-kernel,
Pavel Emelyanov, Konstantin Khorenko, Pavel Tikhomirov,
Lennart Poettering, Eric W . Biederman, Kay Sievers
Oleg Nesterov (1):
introduce the walk_process_tree() helper
Pavel Tikhomirov (1):
prctl: propagate has_child_subreaper flag to every descendant
include/linux/sched.h | 3 +++
kernel/fork.c | 42 +++++++++++++++++++++++++++++++++++++++---
kernel/sys.c | 22 ++++++++++++++++++++++
3 files changed, 64 insertions(+), 3 deletions(-)
--
2.9.3
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH 1/2] introduce the walk_process_tree() helper
2017-01-30 15:06 [PATCH v4 0/2] prctl: make PR_SET_CHILD_SUBREAPER deterministic Pavel Tikhomirov
@ 2017-01-30 15:06 ` Pavel Tikhomirov
2017-01-30 15:06 ` [PATCH v4 2/2] prctl: propagate has_child_subreaper flag to every descendant Pavel Tikhomirov
1 sibling, 0 replies; 6+ messages in thread
From: Pavel Tikhomirov @ 2017-01-30 15:06 UTC (permalink / raw)
To: Ingo Molnar
Cc: Peter Zijlstra, Andrew Morton, Cyrill Gorcunov, John Stultz,
Thomas Gleixner, Oleg Nesterov, Nicolas Pitre, Michal Hocko,
Stanislav Kinsburskiy, Mateusz Guzik, linux-kernel,
Pavel Emelyanov, Konstantin Khorenko, Pavel Tikhomirov,
Lennart Poettering, Eric W . Biederman, Kay Sievers
From: Oleg Nesterov <oleg@redhat.com>
Add the new helper to walk the process tree, the next patch adds a user.
Note that it visits the group leaders only, proc_visitor can do
for_each_thread itself or we can trivially extend walk_process_tree() to
do this.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
---
include/linux/sched.h | 3 +++
kernel/fork.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ad3ec9e..7f8ab91 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3067,6 +3067,9 @@ extern bool current_is_single_threaded(void);
#define for_each_process_thread(p, t) \
for_each_process(p) for_each_thread(p, t)
+typedef int (*proc_visitor)(struct task_struct *p, void *data);
+void walk_process_tree(struct task_struct *top, proc_visitor, void *);
+
static inline int get_nr_threads(struct task_struct *tsk)
{
return tsk->signal->nr_threads;
diff --git a/kernel/fork.c b/kernel/fork.c
index 11c5c8a..135b7a4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2053,6 +2053,38 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
}
#endif
+void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
+{
+ struct task_struct *leader, *parent, *child;
+ int res;
+
+ read_lock(&tasklist_lock);
+ leader = top = top->group_leader;
+down:
+ for_each_thread(leader, parent) {
+ list_for_each_entry(child, &parent->children, sibling) {
+ res = visitor(child, data);
+ if (res) {
+ if (res < 0)
+ goto out;
+ leader = child;
+ goto down;
+ }
+up:
+ ;
+ }
+ }
+
+ if (leader != top) {
+ child = leader;
+ parent = child->real_parent;
+ leader = parent->group_leader;
+ goto up;
+ }
+out:
+ read_unlock(&tasklist_lock);
+}
+
#ifndef ARCH_MIN_MMSTRUCT_ALIGN
#define ARCH_MIN_MMSTRUCT_ALIGN 0
#endif
--
2.9.3
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH v4 2/2] prctl: propagate has_child_subreaper flag to every descendant
2017-01-30 15:06 [PATCH v4 0/2] prctl: make PR_SET_CHILD_SUBREAPER deterministic Pavel Tikhomirov
2017-01-30 15:06 ` [PATCH 1/2] introduce the walk_process_tree() helper Pavel Tikhomirov
@ 2017-01-30 15:06 ` Pavel Tikhomirov
2017-01-31 18:24 ` Oleg Nesterov
1 sibling, 1 reply; 6+ messages in thread
From: Pavel Tikhomirov @ 2017-01-30 15:06 UTC (permalink / raw)
To: Ingo Molnar
Cc: Peter Zijlstra, Andrew Morton, Cyrill Gorcunov, John Stultz,
Thomas Gleixner, Oleg Nesterov, Nicolas Pitre, Michal Hocko,
Stanislav Kinsburskiy, Mateusz Guzik, linux-kernel,
Pavel Emelyanov, Konstantin Khorenko, Pavel Tikhomirov,
Lennart Poettering, Eric W . Biederman, Kay Sievers
If process forks some children when it has is_child_subreaper
flag enabled they will inherit has_child_subreaper flag - first
group, when is_child_subreaper is disabled forked children will
not inherit it - second group. So child-subreaper does not reparent
all his descendants when their parents die. Having these two
differently behaving groups can lead to confusion. Also it is
a problem for CRIU, as when we restore process tree we need to
somehow determine which descendants belong to which group and
much harder - to put them exactly to these group.
To simplify these we can add a propagation of has_child_subreaper
flag on PR_SET_CHILD_SUBREAPER, walking all descendants of child-
subreaper to setup has_child_subreaper flag.
In common cases when process like systemd first sets itself to
be a child-subreaper and only after that forks its services, we will
have zero-length list of descendants to walk. Testing with binary
subtree of 2^15 processes prctl took < 0.007 sec and has shown close
to linear dependency(~0.2 * n * usec) on lower numbers of processes.
Moreover, I doubt someone intentionaly pre-forks the children whitch
should reparent to init before becoming subreaper, because some our
ancestor migh have had is_child_subreaper flag while forking our
sub-tree and our childs will all inherit has_child_subreaper flag,
and we have no way to influence it. And only way to check if we have
no has_child_subreaper flag is to create some childs, kill them and
see where they will reparent to.
Using walk_process_tree helper to walk subtree, thanks to Oleg! Timing
seems to be the same.
Optimize:
a) When descendant already has has_child_subreaper flag all his subtree
has it too already.
* for a) to be true need to move has_child_subreaper inheritance under
the same tasklist_lock with adding task to its ->real_parent->children
as without it process can inherit zero has_child_subreaper, then we
set 1 to it's parent flag, check that parent has no more children, and
only after child with wrong flag is added to the tree.
* Also make these inheritance more clear by using real_parent instead of
current, as on clone(CLONE_PARENT) if current has is_child_subreaper
and real_parent has no is_child_subreaper or has_child_subreaper, child
will have has_child_subreaper flag set without actually having a
subreaper in it's ancestors.
b) When some descendant is child_reaper, it's subtree is in different
pidns from us(original child-subreaper) and processes from other pidns
will never reparent to us.
So we can skip their(a,b) subtree from walk.
v2: switch to walk_process_tree() general helper, move
has_child_subreaper inheritance
v3: remove csr_descendant leftover, change current to real_parent
in has_child_subreaper inheritance
v4: small commit message fix
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
---
kernel/fork.c | 10 +++++++---
kernel/sys.c | 22 ++++++++++++++++++++++
2 files changed, 29 insertions(+), 3 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index 135b7a4..c814e59 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1367,9 +1367,6 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
sig->oom_score_adj = current->signal->oom_score_adj;
sig->oom_score_adj_min = current->signal->oom_score_adj_min;
- sig->has_child_subreaper = current->signal->has_child_subreaper ||
- current->signal->is_child_subreaper;
-
mutex_init(&sig->cred_guard_mutex);
return 0;
@@ -1800,6 +1797,13 @@ static __latent_entropy struct task_struct *copy_process(
p->signal->leader_pid = pid;
p->signal->tty = tty_kref_get(current->signal->tty);
+ /*
+ * Inherit has_child_subreaper flag under the same
+ * tasklist_lock with adding child to the process tree
+ * for propagate_has_child_subreaper optimization.
+ */
+ p->signal->has_child_subreaper = p->real_parent->signal->has_child_subreaper ||
+ 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_PGID);
diff --git a/kernel/sys.c b/kernel/sys.c
index 842914e..0e4d566 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2063,6 +2063,24 @@ static int prctl_get_tid_address(struct task_struct *me, int __user **tid_addr)
}
#endif
+static int propagate_has_child_subreaper(struct task_struct *p, void *data)
+{
+ /*
+ * If task has has_child_subreaper - all its decendants
+ * already have these flag too and new decendants will
+ * inherit it on fork, skip them.
+ *
+ * If we've found child_reaper - skip descendants in
+ * it's subtree as they will never get out pidns.
+ */
+ if (p->signal->has_child_subreaper ||
+ is_child_reaper(task_pid(p)))
+ return 0;
+
+ p->signal->has_child_subreaper = 1;
+ return 1;
+}
+
SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
unsigned long, arg4, unsigned long, arg5)
{
@@ -2214,6 +2232,10 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
break;
case PR_SET_CHILD_SUBREAPER:
me->signal->is_child_subreaper = !!arg2;
+ if (!arg2)
+ break;
+
+ walk_process_tree(me, propagate_has_child_subreaper, NULL);
break;
case PR_GET_CHILD_SUBREAPER:
error = put_user(me->signal->is_child_subreaper,
--
2.9.3
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v4 2/2] prctl: propagate has_child_subreaper flag to every descendant
2017-01-30 15:06 ` [PATCH v4 2/2] prctl: propagate has_child_subreaper flag to every descendant Pavel Tikhomirov
@ 2017-01-31 18:24 ` Oleg Nesterov
0 siblings, 0 replies; 6+ messages in thread
From: Oleg Nesterov @ 2017-01-31 18:24 UTC (permalink / raw)
To: Pavel Tikhomirov
Cc: Ingo Molnar, Peter Zijlstra, Andrew Morton, Cyrill Gorcunov,
John Stultz, Thomas Gleixner, Nicolas Pitre, Michal Hocko,
Stanislav Kinsburskiy, Mateusz Guzik, linux-kernel,
Pavel Emelyanov, Konstantin Khorenko, Lennart Poettering,
Eric W . Biederman, Kay Sievers
On 01/30, Pavel Tikhomirov wrote:
>
> Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
> ---
> kernel/fork.c | 10 +++++++---
> kernel/sys.c | 22 ++++++++++++++++++++++
> 2 files changed, 29 insertions(+), 3 deletions(-)
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH 1/2] introduce the walk_process_tree() helper
2017-01-30 14:48 [PATCH v3 0/2] prctl: make PR_SET_CHILD_SUBREAPER deterministic Pavel Tikhomirov
@ 2017-01-30 14:48 ` Pavel Tikhomirov
0 siblings, 0 replies; 6+ messages in thread
From: Pavel Tikhomirov @ 2017-01-30 14:48 UTC (permalink / raw)
To: Ingo Molnar
Cc: Peter Zijlstra, Andrew Morton, Cyrill Gorcunov, John Stultz,
Thomas Gleixner, Oleg Nesterov, Nicolas Pitre, Michal Hocko,
Stanislav Kinsburskiy, Mateusz Guzik, linux-kernel,
Pavel Emelyanov, Konstantin Khorenko, Pavel Tikhomirov,
Lennart Poettering, Eric W . Biederman, Kay Sievers
From: Oleg Nesterov <oleg@redhat.com>
Add the new helper to walk the process tree, the next patch adds a user.
Note that it visits the group leaders only, proc_visitor can do
for_each_thread itself or we can trivially extend walk_process_tree() to
do this.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
---
include/linux/sched.h | 3 +++
kernel/fork.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ad3ec9e..7f8ab91 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3067,6 +3067,9 @@ extern bool current_is_single_threaded(void);
#define for_each_process_thread(p, t) \
for_each_process(p) for_each_thread(p, t)
+typedef int (*proc_visitor)(struct task_struct *p, void *data);
+void walk_process_tree(struct task_struct *top, proc_visitor, void *);
+
static inline int get_nr_threads(struct task_struct *tsk)
{
return tsk->signal->nr_threads;
diff --git a/kernel/fork.c b/kernel/fork.c
index 11c5c8a..135b7a4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2053,6 +2053,38 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
}
#endif
+void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
+{
+ struct task_struct *leader, *parent, *child;
+ int res;
+
+ read_lock(&tasklist_lock);
+ leader = top = top->group_leader;
+down:
+ for_each_thread(leader, parent) {
+ list_for_each_entry(child, &parent->children, sibling) {
+ res = visitor(child, data);
+ if (res) {
+ if (res < 0)
+ goto out;
+ leader = child;
+ goto down;
+ }
+up:
+ ;
+ }
+ }
+
+ if (leader != top) {
+ child = leader;
+ parent = child->real_parent;
+ leader = parent->group_leader;
+ goto up;
+ }
+out:
+ read_unlock(&tasklist_lock);
+}
+
#ifndef ARCH_MIN_MMSTRUCT_ALIGN
#define ARCH_MIN_MMSTRUCT_ALIGN 0
#endif
--
2.9.3
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH 1/2] introduce the walk_process_tree() helper
2017-01-27 10:05 [PATCH v2 0/2] prctl: make PR_SET_CHILD_SUBREAPER deterministic Pavel Tikhomirov
@ 2017-01-27 10:05 ` Pavel Tikhomirov
0 siblings, 0 replies; 6+ messages in thread
From: Pavel Tikhomirov @ 2017-01-27 10:05 UTC (permalink / raw)
To: Ingo Molnar
Cc: Peter Zijlstra, Andrew Morton, Cyrill Gorcunov, John Stultz,
Thomas Gleixner, Oleg Nesterov, Nicolas Pitre, Michal Hocko,
Stanislav Kinsburskiy, Mateusz Guzik, linux-kernel,
Pavel Emelyanov, Konstantin Khorenko, Pavel Tikhomirov,
Lennart Poettering, Eric W . Biederman, Kay Sievers
From: Oleg Nesterov <oleg@redhat.com>
Add the new helper to walk the process tree, the next patch adds a user.
Note that it visits the group leaders only, proc_visitor can do
for_each_thread itself or we can trivially extend walk_process_tree() to
do this.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
---
include/linux/sched.h | 3 +++
kernel/fork.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ad3ec9e..7f8ab91 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3067,6 +3067,9 @@ extern bool current_is_single_threaded(void);
#define for_each_process_thread(p, t) \
for_each_process(p) for_each_thread(p, t)
+typedef int (*proc_visitor)(struct task_struct *p, void *data);
+void walk_process_tree(struct task_struct *top, proc_visitor, void *);
+
static inline int get_nr_threads(struct task_struct *tsk)
{
return tsk->signal->nr_threads;
diff --git a/kernel/fork.c b/kernel/fork.c
index 11c5c8a..135b7a4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2053,6 +2053,38 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
}
#endif
+void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
+{
+ struct task_struct *leader, *parent, *child;
+ int res;
+
+ read_lock(&tasklist_lock);
+ leader = top = top->group_leader;
+down:
+ for_each_thread(leader, parent) {
+ list_for_each_entry(child, &parent->children, sibling) {
+ res = visitor(child, data);
+ if (res) {
+ if (res < 0)
+ goto out;
+ leader = child;
+ goto down;
+ }
+up:
+ ;
+ }
+ }
+
+ if (leader != top) {
+ child = leader;
+ parent = child->real_parent;
+ leader = parent->group_leader;
+ goto up;
+ }
+out:
+ read_unlock(&tasklist_lock);
+}
+
#ifndef ARCH_MIN_MMSTRUCT_ALIGN
#define ARCH_MIN_MMSTRUCT_ALIGN 0
#endif
--
2.9.3
^ permalink raw reply related [flat|nested] 6+ messages in thread
end of thread, other threads:[~2017-01-31 18:26 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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