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SubjectRe: [PATCH] Fix check after use in kernel/exit.c
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From: Ingo Molnar <mingo@elte.hu>
Date: Sun, 9 Mar 2008 12:48:44 +0100

>
> * WANG Cong <xiyou.wangcong@gmail.com> wrote:
>
> > > actually, i unapplied it again because the patch is wrong:
> > > mm_release() has side-effects for kernel threads such as the
> > > deactivate_mm() [which is important even if the user-mm is NULL]. If
> > > the NULL mm dereference can really trigger then it should be avoided
> > > within mm_release().
> >
> > Do you mean that the NULL check should be moved into mm_release()?
>
> yes - we need to run deactivate_mm() for kernel threads.


Thank you for your kind hints.

Here is an updated version. Please check.

---->

From: WANG Cong <xiyou.wangcong@gmail.com>
Subject: [PATCH] Fix check after use in kernel/exit.c

As suggested by Ingo, the NULL deference check should be moved
into mm_release().

Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>

---
kernel/exit.c | 2 --
kernel/fork.c | 2 ++
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 53872bf..b88244a 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -583,8 +583,6 @@ static void exit_mm(struct task_struct * tsk)
struct mm_struct *mm = tsk->mm;

mm_release(tsk, mm);
- if (!mm)
- return;
/*
* Serialize with any possible pending coredump.
* We must hold mmap_sem around checking core_waiters
diff --git a/kernel/fork.c b/kernel/fork.c
index dd249c3..7683c5f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -464,6 +464,8 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
{
struct completion *vfork_done = tsk->vfork_done;

+ if (!mm)
+ return;
/* Get rid of any cached register state */
deactivate_mm(tsk, mm);

--
1.5.2.4



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