Second parameter of find_new_reaper() and the similarity of its name
and find_child_reaper()'s name confuse a reader.
Rename find_child_reaper() for better conformity of its name and its
function. Also delete the second parameter of find_new_reaper().
These both improve modularity.
Signed-off-by: Kirill Tkhai <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Andrew Morton <[email protected]>
---
kernel/exit.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index 22fcc05..ae60a4d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -450,7 +450,7 @@ static struct task_struct *find_alive_thread(struct task_struct *p)
return NULL;
}
-static struct task_struct *find_child_reaper(struct task_struct *father)
+static void exit_pidns_child_reaper(struct task_struct *father)
__releases(&tasklist_lock)
__acquires(&tasklist_lock)
{
@@ -458,12 +458,12 @@ static struct task_struct *find_child_reaper(struct task_struct *father)
struct task_struct *reaper = pid_ns->child_reaper;
if (likely(reaper != father))
- return reaper;
+ return;
reaper = find_alive_thread(father);
if (reaper) {
pid_ns->child_reaper = reaper;
- return reaper;
+ return;
}
write_unlock_irq(&tasklist_lock);
@@ -473,8 +473,6 @@ static struct task_struct *find_child_reaper(struct task_struct *father)
}
zap_pid_ns_processes(pid_ns);
write_lock_irq(&tasklist_lock);
-
- return father;
}
/*
@@ -484,15 +482,21 @@ static struct task_struct *find_child_reaper(struct task_struct *father)
* child_subreaper for its children (like a service manager)
* 3. give it to the init process (PID 1) in our pid namespace
*/
-static struct task_struct *find_new_reaper(struct task_struct *father,
- struct task_struct *child_reaper)
+static struct task_struct *find_new_reaper(struct task_struct *father)
{
- struct task_struct *thread, *reaper;
+ struct task_struct *thread, *reaper, *child_reaper;
thread = find_alive_thread(father);
if (thread)
return thread;
+ child_reaper = task_active_pid_ns(father)->child_reaper;
+ /*
+ * child_reaper doesn't have children after zap_pid_ns_processes(),
+ * therefore it can't enter this function.
+ */
+ BUG_ON(child_reaper == father);
+
if (father->signal->has_child_subreaper) {
/*
* Find the first ->is_child_subreaper ancestor in our pid_ns.
@@ -557,11 +561,11 @@ static void forget_original_parent(struct task_struct *father,
exit_ptrace(father, dead);
/* Can drop and reacquire tasklist_lock */
- reaper = find_child_reaper(father);
+ exit_pidns_child_reaper(father);
if (list_empty(&father->children))
return;
- reaper = find_new_reaper(father, reaper);
+ reaper = find_new_reaper(father);
list_for_each_entry(p, &father->children, sibling) {
for_each_thread(p, t) {
t->real_parent = reaper;
On 06/16, Kirill Tkhai wrote:
>
> Second parameter of find_new_reaper() and the similarity of its name
> and find_child_reaper()'s name confuse a reader.
OK, I agree that
reaper = find_child_reaper(father);
...
reaper = find_new_reaper(father, reaper);
can look confusing and probably deserves a cleanup. How about the patch
below then?
> Rename find_child_reaper() for better conformity of its name and its
> function.
I never argueus with renames ;) Probably the new name looks better.
> Also delete the second parameter of find_new_reaper().
Yes, we can do this. But this 2nd argument avoids another another
task_active_pid_ns(father)->child_reaper, so this is optimization.
I agree, this optimization is minor, but still I think this change
needs some justification.
> +static struct task_struct *find_new_reaper(struct task_struct *father)
> {
> - struct task_struct *thread, *reaper;
> + struct task_struct *thread, *reaper, *child_reaper;
>
> thread = find_alive_thread(father);
> if (thread)
> return thread;
>
> + child_reaper = task_active_pid_ns(father)->child_reaper;
> + /*
> + * child_reaper doesn't have children after zap_pid_ns_processes(),
> + * therefore it can't enter this function.
> + */
> + BUG_ON(child_reaper == father);
Yes, we can add this BUG_ON(). But please see the comments in
zap_pid_ns_processes(). We can change zap_pid_ns_processes() so that
it returns with non-empty ->children list due to EXIT_DEAD children.
Unlikely we will actually do this, at least soon, so I won't argue
with this BUG_ON().
But. In this case it would be better to add it into forget_original_parent(),
reaper = find_new_reaper(...);
BUG_ON(reaper == father);
Oh. Off-topic, but this reminds me that I forgot about another bug with
->has_child_subreaper... this needs another discussion.
Oleg.
--- x/kernel/exit.c
+++ x/kernel/exit.c
@@ -551,17 +551,17 @@ static void reparent_leader(struct task_
static void forget_original_parent(struct task_struct *father,
struct list_head *dead)
{
- struct task_struct *p, *t, *reaper;
+ struct task_struct *p, *t, *child_reaper, *reaper;
if (unlikely(!list_empty(&father->ptraced)))
exit_ptrace(father, dead);
/* Can drop and reacquire tasklist_lock */
- reaper = find_child_reaper(father);
+ child_reaper = find_child_reaper(father);
if (list_empty(&father->children))
return;
- reaper = find_new_reaper(father, reaper);
+ reaper = find_new_reaper(father, child_reaper);
list_for_each_entry(p, &father->children, sibling) {
for_each_thread(p, t) {
t->real_parent = reaper;
forgot to mention,
On 06/16, Oleg Nesterov wrote:
>
> On 06/16, Kirill Tkhai wrote:
> >
> > + * child_reaper doesn't have children after zap_pid_ns_processes(),
> > + * therefore it can't enter this function.
> > + */
> > + BUG_ON(child_reaper == father);
>
> Yes, we can add this BUG_ON(). But please see the comments in
> zap_pid_ns_processes(). We can change zap_pid_ns_processes() so that
> it returns with non-empty ->children list due to EXIT_DEAD children.
>
> Unlikely we will actually do this, at least soon, so I won't argue
> with this BUG_ON().
>
> But. In this case it would be better to add it into forget_original_parent(),
>
> reaper = find_new_reaper(...);
> BUG_ON(reaper == father);
because this way:
1. This BUG_ON() will still be valid even if we actually change
zap_pid_ns_processes() to return with EXIT_DEAD children
2. If we really want this sanity check, we should not tie it to
->child_reaper case.
OTOH. If for some reason you want to check ->child_reaper only, then
you should probably do this right after list_empty(&father->children)
check, or at least before find_alive_thread(). Because otherwise it
looks confusing, it looks as if "child_reaper == father" is only wrong
if find_alive_thread(father) fails.
Oleg.
В Вт, 16/06/2015 в 21:27 +0200, Oleg Nesterov пишет:
> On 06/16, Kirill Tkhai wrote:
> >
> > Second parameter of find_new_reaper() and the similarity of its name
> > and find_child_reaper()'s name confuse a reader.
>
> OK, I agree that
>
> reaper = find_child_reaper(father);
> ...
> reaper = find_new_reaper(father, reaper);
>
> can look confusing and probably deserves a cleanup. How about the patch
> below then?
Good, IMO it improves the readability.
>
> > Rename find_child_reaper() for better conformity of its name and its
> > function.
>
> I never argueus with renames ;) Probably the new name looks better.
>
> > Also delete the second parameter of find_new_reaper().
>
> Yes, we can do this. But this 2nd argument avoids another another
> task_active_pid_ns(father)->child_reaper, so this is optimization.
>
> I agree, this optimization is minor, but still I think this change
> needs some justification.
It looks like gcc inlines both of these function, so it seems there won't
be a problem...
>
> > +static struct task_struct *find_new_reaper(struct task_struct *father)
> > {
> > - struct task_struct *thread, *reaper;
> > + struct task_struct *thread, *reaper, *child_reaper;
> >
> > thread = find_alive_thread(father);
> > if (thread)
> > return thread;
> >
> > + child_reaper = task_active_pid_ns(father)->child_reaper;
> > + /*
> > + * child_reaper doesn't have children after zap_pid_ns_processes(),
> > + * therefore it can't enter this function.
> > + */
> > + BUG_ON(child_reaper == father);
>
> Yes, we can add this BUG_ON(). But please see the comments in
> zap_pid_ns_processes(). We can change zap_pid_ns_processes() so that
> it returns with non-empty ->children list due to EXIT_DEAD children.
Yes, I saw. Since zap_pid_ns_processes() waits for nr_hashed,
and __unhash_process() deletes from pid chain and sibling list
at the same time, pid_ns child_reaper can't have a child after
nr_hashed == init_pids.
> Unlikely we will actually do this, at least soon, so I won't argue
> with this BUG_ON().
>
> But. In this case it would be better to add it into forget_original_parent(),
>
> reaper = find_new_reaper(...);
> BUG_ON(reaper == father);
Yeah, I'm agree.
> Oh. Off-topic, but this reminds me that I forgot about another bug with
> ->has_child_subreaper... this needs another discussion.
>
> Oleg.
>
> --- x/kernel/exit.c
> +++ x/kernel/exit.c
> @@ -551,17 +551,17 @@ static void reparent_leader(struct task_
> static void forget_original_parent(struct task_struct *father,
> struct list_head *dead)
> {
> - struct task_struct *p, *t, *reaper;
> + struct task_struct *p, *t, *child_reaper, *reaper;
>
> if (unlikely(!list_empty(&father->ptraced)))
> exit_ptrace(father, dead);
>
> /* Can drop and reacquire tasklist_lock */
> - reaper = find_child_reaper(father);
> + child_reaper = find_child_reaper(father);
> if (list_empty(&father->children))
> return;
>
> - reaper = find_new_reaper(father, reaper);
> + reaper = find_new_reaper(father, child_reaper);
> list_for_each_entry(p, &father->children, sibling) {
> for_each_thread(p, t) {
> t->real_parent = reaper;
>
Thanks,
Kirill
В Вт, 16/06/2015 в 22:03 +0200, Oleg Nesterov пишет:
> forgot to mention,
>
> On 06/16, Oleg Nesterov wrote:
> >
> > On 06/16, Kirill Tkhai wrote:
> > >
> > > + * child_reaper doesn't have children after zap_pid_ns_processes(),
> > > + * therefore it can't enter this function.
> > > + */
> > > + BUG_ON(child_reaper == father);
> >
> > Yes, we can add this BUG_ON(). But please see the comments in
> > zap_pid_ns_processes(). We can change zap_pid_ns_processes() so that
> > it returns with non-empty ->children list due to EXIT_DEAD children.
> >
> > Unlikely we will actually do this, at least soon, so I won't argue
> > with this BUG_ON().
> >
> > But. In this case it would be better to add it into forget_original_parent(),
> >
> > reaper = find_new_reaper(...);
> > BUG_ON(reaper == father);
>
> because this way:
>
> 1. This BUG_ON() will still be valid even if we actually change
> zap_pid_ns_processes() to return with EXIT_DEAD children
>
> 2. If we really want this sanity check, we should not tie it to
> ->child_reaper case.
>
> OTOH. If for some reason you want to check ->child_reaper only, then
> you should probably do this right after list_empty(&father->children)
> check, or at least before find_alive_thread(). Because otherwise it
> looks confusing, it looks as if "child_reaper == father" is only wrong
> if find_alive_thread(father) fails.
Sure, it's more logical. Thanks, Oleg.