Re: [PATCH] on CONFIG_MM_OWNER=y, kernel panic is possible. take2

[Balbir Singh]

KOSAKI Motohiro wrote:
>> I'd word it as
>>
>> /*
>>  * "owner" points to a task that is regarded as the canonical
>>  * user/owner of this mm. All of the following must be true in
>>  * order for it to be changed:
>>  *
>>  * current == mm->owner
>>  * current->mm != mm
>>  * new_owner->mm == mm
>>  * new_owner->alloc_lock is held
>>  */
> 
> Wow, Thank you a lot!
> new version attached.
> 
> Cheers!
> 
> 
> -----------------------------------------------------------
> When mm destruct happend, We should pass mm_update_next_owner() 
> old mm.
> but unfortunately new mm is passed in exec_mmap().
> 
> thus, kernel panic is possible when multi thread process use exec().
> 
> 
> and, owner member comment description is wrong.
> mm->owner don't not necessarily point to thread group leader.
> 
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> CC: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> CC: "Paul Menage" <menage@xxxxxxxxxx>
> CC: "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> 
> ---
>  fs/exec.c                |    2 +-
>  include/linux/mm_types.h |   13 +++++++++++--
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> Index: b/fs/exec.c
> ===================================================================
> --- a/fs/exec.c	2008-05-04 22:57:09.000000000 +0900
> +++ b/fs/exec.c	2008-05-06 15:40:35.000000000 +0900
> @@ -735,7 +735,7 @@ static int exec_mmap(struct mm_struct *m
>  	tsk->active_mm = mm;
>  	activate_mm(active_mm, mm);
>  	task_unlock(tsk);
> -	mm_update_next_owner(mm);
> +	mm_update_next_owner(old_mm);
>  	arch_pick_mmap_layout(mm);
>  	if (old_mm) {
>  		up_read(&old_mm->mmap_sem);
> Index: b/include/linux/mm_types.h
> ===================================================================
> --- a/include/linux/mm_types.h	2008-05-08 09:20:13.000000000 +0900
> +++ b/include/linux/mm_types.h	2008-05-08 09:22:13.000000000 +0900
> @@ -231,8 +231,17 @@ struct mm_struct {
>  	rwlock_t		ioctx_list_lock;	/* aio lock */
>  	struct kioctx		*ioctx_list;
>  #ifdef CONFIG_MM_OWNER
> -	struct task_struct *owner;	/* The thread group leader that */
> -					/* owns the mm_struct.		*/
> +        /*
> +         * "owner" points to a task that is regarded as the canonical
> +         * user/owner of this mm. All of the following must be true in
> +         * order for it to be changed:
> +         *
> +         * current == mm->owner
> +         * current->mm != mm
> +         * new_owner->mm == mm
> +         * new_owner->alloc_lock is held
> +         */
> +	struct task_struct *owner;
>  #endif
> 
>  #ifdef CONFIG_PROC_FS
> 

Looks good to me, but I've not tested it

Acked-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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