Re: [PATCH 01/17] exit: Remove profile_task_exit & profile_munmap

Eric W. Biederman
2022-01-08T16:11:29Z

Al Viro <viro@zeniv.linux.org.uk> writes:

> On Mon, Jan 03, 2022 at 03:32:56PM -0600, Eric W. Biederman wrote:
>> When I say remove I mean remove. All profile_task_exit and
>> profile_munmap do is call a blocking notifier chain. The helpers
>> profile_task_register and profile_task_unregister are not called
>> anywhere in the tree. Which means this is all dead code.
>>
>> So remove the dead code and make it easier to read do_exit.
>
> How about doing the same to profile_handoff_task() and
> task_handoff_register()/task_handoff_unregister(),
> while we are at it? Combined diff would be this:

A very good idea. I have added this incremental patch to my queue.

Eric

From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Sat, 8 Jan 2022 10:03:24 -0600
Subject: [PATCH] exit: Remove profile_handoff_task

All profile_handoff_task does is notify the task_free_notifier chain.
The helpers task_handoff_register and task_handoff_unregister are used
to add and delete entries from that chain and are never called.

So remove the dead code and make it much easier to read and reason
about __put_task_struct.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
include/linux/profile.h | 19 -------------------
kernel/fork.c | 4 +---
kernel/profile.c | 23 -----------------------
3 files changed, 1 insertion(+), 45 deletions(-)

diff --git a/include/linux/profile.h b/include/linux/profile.h
index f7eb2b57d890..11db1ec516e2 100644
--- a/include/linux/profile.h
+++ b/include/linux/profile.h
@@ -61,14 +61,6 @@ static inline void profile_hit(int type, void *ip)
struct task_struct;
struct mm_struct;

-/* task is dead, free task struct ? Returns 1 if
- * the task was taken, 0 if the task should be freed.
- */
-int profile_handoff_task(struct task_struct * task);
-
-int task_handoff_register(struct notifier_block * n);
-int task_handoff_unregister(struct notifier_block * n);
-
#else

#define prof_on 0
@@ -93,17 +85,6 @@ static inline void profile_hit(int type, void *ip)
return;
}

-static inline int task_handoff_register(struct notifier_block * n)
-{
- return -ENOSYS;
-}
-
-static inline int task_handoff_unregister(struct notifier_block * n)
-{
- return -ENOSYS;
-}
-
-#define profile_handoff_task(a) (0)

#endif /* CONFIG_PROFILING */

diff --git a/kernel/fork.c b/kernel/fork.c
index 6f0293cb29c9..494539ecb6d3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -754,9 +754,7 @@ void __put_task_struct(struct task_struct *tsk)
delayacct_tsk_free(tsk);
put_signal_struct(tsk->signal);
sched_core_free(tsk);
-
- if (!profile_handoff_task(tsk))
- free_task(tsk);
+ free_task(tsk);
}
EXPORT_SYMBOL_GPL(__put_task_struct);

diff --git a/kernel/profile.c b/kernel/profile.c
index 9355cc934a96..37640a0bd8a3 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -133,29 +133,6 @@ int __ref profile_init(void)
return -ENOMEM;
}

-/* Profile event notifications */
-
-static ATOMIC_NOTIFIER_HEAD(task_free_notifier);
-
-int profile_handoff_task(struct task_struct *task)
-{
- int ret;
- ret = atomic_notifier_call_chain(&task_free_notifier, 0, task);
- return (ret == NOTIFY_OK) ? 1 : 0;
-}
-
-int task_handoff_register(struct notifier_block *n)
-{
- return atomic_notifier_chain_register(&task_free_notifier, n);
-}
-EXPORT_SYMBOL_GPL(task_handoff_register);
-
-int task_handoff_unregister(struct notifier_block *n)
-{
- return atomic_notifier_chain_unregister(&task_free_notifier, n);
-}
-EXPORT_SYMBOL_GPL(task_handoff_unregister);
-
#if defined(CONFIG_SMP) && defined(CONFIG_PROC_FS)
/*
* Each cpu has a pair of open-addressed hashtables for pending
--
2.29.2