Messages in this thread | | | Date | Fri, 2 Sep 2011 16:00:15 +0200 | From | Oleg Nesterov <> | Subject | Re: + cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc.patch added to -mm tree |
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Forgot to mention, sorry...
That said, I believe the patch is correct and should fix the problem.
On 09/02, Oleg Nesterov wrote: > > > From: Ben Blum <bblum@andrew.cmu.edu> > > > > Fix unstable tasklist locking in cgroup_attach_proc. > > > > According to this thread - https://lkml.org/lkml/2011/7/27/243 - RCU is > > not sufficient to guarantee the tasklist is stable w.r.t. de_thread and > > exit. Taking tasklist_lock for reading, instead of rcu_read_lock, ensures > > proper exclusion. > > I still think we should avoid the global lock. > > In any case, with tasklist or siglock, > > > - rcu_read_lock(); > > + read_lock(&tasklist_lock); > > if (!thread_group_leader(leader)) { > > /* > > * a race with de_thread from another thread's exec() may strip > > @@ -2036,7 +2036,7 @@ int cgroup_attach_proc(struct cgroup *cg > > * throw this task away and try again (from cgroup_procs_write); > > * this is "double-double-toil-and-trouble-check locking". > > */ > > - rcu_read_unlock(); > > + read_unlock(&tasklist_lock); > > retval = -EAGAIN; > > this check+comment becomes completely pointless and imho very confusing. > > Oleg.
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