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

[Yang Shi]

On 4/18/19 6:05 AM, Laurent Dufour wrote:
> Le 18/04/2019 Ã 15:03, Michal Hocko a ÃcritÂ:
> > Michal has posted the same patch few days ago 
> > http://lkml.kernel.org/r/20190417120347.15397-1-mkoutny@xxxxxxxx
>
> Oups, sorry for the noise, I missed it.

Yes, Michal already posted a similar patch. Anyway, thanks for catching 
this.

> > 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@xxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
> > > ---
> > > Â mm/util.c | 4 ++--
> > > Â 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)
> > > ÂÂÂÂÂ if (!mm->arg_end)
> > > ÂÂÂÂÂÂÂÂÂ goto out_mm;ÂÂÂ /* Shh! No looking before we're done */
> > > Â -ÂÂÂ down_read(&mm->mmap_sem);
> > > +ÂÂÂ spin_lock(&mm->arg_lock);
> > > ÂÂÂÂÂ arg_start = mm->arg_start;
> > > ÂÂÂÂÂ arg_end = mm->arg_end;
> > > ÂÂÂÂÂ env_start = mm->env_start;
> > > ÂÂÂÂÂ env_end = mm->env_end;
> > > -ÂÂÂ up_read(&mm->mmap_sem);
> > > +ÂÂÂ spin_unlock(&mm->arg_lock);
> > > Â ÂÂÂÂÂ len = arg_end - arg_start;
> > > Â --
> > > 2.21.0