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[tip:x86/asm] kthread: Pin the stack via try_get_task_stack()/put_task_stack() in to_live_kthread() function

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Commit-ID:  23196f2e5f5d810578a772785807dcdc2b9fdce9
Gitweb:     http://git.kernel.org/tip/23196f2e5f5d810578a772785807dcdc2b9fdce9
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Thu, 15 Sep 2016 22:45:44 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 16 Sep 2016 09:18:53 +0200

kthread: Pin the stack via try_get_task_stack()/put_task_stack() in to_live_kthread() function

get_task_struct(tsk) no longer pins tsk->stack so all users of
to_live_kthread() should do try_get_task_stack/put_task_stack to protect
"struct kthread" which lives on kthread's stack.

TODO: Kill to_live_kthread(), perhaps we can even kill "struct kthread" too,
and rework kthread_stop(), it can use task_work_add() to sync with the exiting
kernel thread.

Message-Id: <20160629180357.GA7178@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jann Horn <jann@thejh.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/cb9b16bbc19d4aea4507ab0552e4644c1211d130.1474003868.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/kthread.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 9ff173d..4ab4c37 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -64,7 +64,7 @@ static inline struct kthread *to_kthread(struct task_struct *k)
 static struct kthread *to_live_kthread(struct task_struct *k)
 {
 	struct completion *vfork = ACCESS_ONCE(k->vfork_done);
-	if (likely(vfork))
+	if (likely(vfork) && try_get_task_stack(k))
 		return __to_kthread(vfork);
 	return NULL;
 }
@@ -425,8 +425,10 @@ void kthread_unpark(struct task_struct *k)
 {
 	struct kthread *kthread = to_live_kthread(k);
 
-	if (kthread)
+	if (kthread) {
 		__kthread_unpark(k, kthread);
+		put_task_stack(k);
+	}
 }
 EXPORT_SYMBOL_GPL(kthread_unpark);
 
@@ -455,6 +457,7 @@ int kthread_park(struct task_struct *k)
 				wait_for_completion(&kthread->parked);
 			}
 		}
+		put_task_stack(k);
 		ret = 0;
 	}
 	return ret;
@@ -490,6 +493,7 @@ int kthread_stop(struct task_struct *k)
 		__kthread_unpark(k, kthread);
 		wake_up_process(k);
 		wait_for_completion(&kthread->exited);
+		put_task_stack(k);
 	}
 	ret = k->exit_code;
 	put_task_struct(k);

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[PATCH v2 0/8] thread_info cleanups and stack caching Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
  [PATCH v2 1/8] x86/entry/64: Fix a minor comment rebase error Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] x86/entry/64: Fix a minor comment rebase error tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-16 11:20 +0200
  [PATCH v2 4/8] x86/dumpstack: Pin the target stack when dumping it Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-16 11:20 +0200
      Re: [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-16 14:00 +0200
        Re: [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-16 14:30 +0200
          Re: [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it Ingo Molnar <mingo@kernel.org> - 2016-09-16 15:00 +0200
            [PATCH] x86/dumpstack: remove NULL task pointer convention Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-16 15:10 +0200
  [PATCH v2 6/8] lib/syscall: Pin the task stack in collect_syscall() Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] lib/syscall: Pin the task stack in collect_syscall() tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-16 11:20 +0200
  [PATCH v2 8/8] fork: Cache two thread stacks per cpu if CONFIG_VMAP_STACK is set Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] fork: Optimize task creation by caching two thread  stacks per CPU if CONFIG_VMAP_STACK=y tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-16 11:30 +0200
  [PATCH v2 3/8] kthread: to_live_kthread() needs try_get_task_stack() Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] kthread: Pin the stack via  try_get_task_stack()/put_task_stack() in to_live_kthread() function tip-bot for Oleg Nesterov <tipbot@zytor.com> - 2016-09-16 11:20 +0200

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