Re: [PATCH] mm: use mm.arg_lock in get_cmdline()

Michal Hocko
2019-04-18T13:03:15Z

Michal has posted the same patch few days ago http://lkml.kernel.org/r/20190417120347.15397-1-mkoutny@suse.com

On Thu 18-04-19 14:58:27, Laurent Dufour wrote:
> The commit 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end
> and env_start|end in mm_struct") introduce the spinlock arg_lock to protect
> the arg_* and env_* field of the mm_struct structure.
>
> While reading the code, I found that this new spinlock was not used in
> get_cmdline() to protect access to these fields.
>
> Fixing this even if there is no issue reported yet for this.
>
> Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct")
> Cc: Yang Shi <yang.shi@linux.alibaba.com>
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
> ---
> mm/util.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/util.c b/mm/util.c
> index 05a464929b3e..789760c3028b 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen)
> if (!mm->arg_end)
> goto out_mm; /* Shh! No looking before we're done */
>
> - down_read(&mm->mmap_sem);
> + spin_lock(&mm->arg_lock);
> arg_start = mm->arg_start;
> arg_end = mm->arg_end;
> env_start = mm->env_start;
> env_end = mm->env_end;
> - up_read(&mm->mmap_sem);
> + spin_unlock(&mm->arg_lock);
>
> len = arg_end - arg_start;
>
> --
> 2.21.0

--
Michal Hocko
SUSE Labs