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

[Laurent Dufour]

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.

> 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>
> > ---
> >   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