linux-kernel - Re: [PATCH 01/17] exit: Remove profile_task_exit & profile

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Message-ID: <87fspyw6m0.fsf@email.froward.int.ebiederm.org>
Date:   Sat, 08 Jan 2022 10:10:47 -0600
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Kees Cook <keescook@...omium.org>, linux-api@...r.kernel.org
Subject: Re: [PATCH 01/17] exit: Remove profile_task_exit & profile_munmap

Al Viro <viro@...iv.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@...ssion.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@...iv.linux.org.uk>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.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