Messages in this thread | | | From | (Eric W. Biederman) | Date | Wed, 07 Jun 2017 09:08:30 -0500 | Subject | Re: [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist_lock |
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Oleg Nesterov <oleg@redhat.com> writes:
> Hi Eric, > > I'll try very much to read this series tomorrow, can't do this today... > > On 06/06, Eric W. Biederman wrote: >> >> @@ -1380,13 +1380,6 @@ int do_prlimit(struct task_struct *tsk, unsigned int resource, >> return -EPERM; >> } >> >> - /* protect tsk->signal and tsk->sighand from disappearing */ >> - read_lock(&tasklist_lock); >> - if (!tsk->sighand) { >> - retval = -ESRCH; >> - goto out; >> - } > > Yes, the comment is wrong. > > However we do need read_lock(tasklist_lock) to access ->group_leader. And the > ->sighand != NULL check ensures that ->group_leader is the valid > pointer.
As of 4.12-rc1 The code does not access group_leader anymore.
> Also, update_rlimit_cpu() is not safe without tasklist / sighand-check. > > We can probably change this code to rely on rcu.
Good point a NULL sighand will cause update_rlimit_cpu to OOPS.
Grr. There is a point in my tree where this is perfectly safe. But not at this point. Consider this patch dropped for the moment.
Eric
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