From: Ben Blum Date: Wed, 2 Nov 2011 20:38:05 +0000 (-0700) Subject: cgroups: more safe tasklist locking in cgroup_attach_proc X-Git-Tag: firefly_0821_release~3680^2~4226^2~40 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=33ef6b6984403a688189317ef46bb3caab3b70e0;p=firefly-linux-kernel-4.4.55.git cgroups: more safe tasklist locking in cgroup_attach_proc 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. Signed-off-by: Ben Blum Acked-by: Paul Menage Cc: Oleg Nesterov Cc: Frederic Weisbecker Cc: "Paul E. McKenney" Cc: Neil Brown Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 453100a4159d..64b0e73402df 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2027,7 +2027,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) goto out_free_group_list; /* prevent changes to the threadgroup list while we take a snapshot. */ - 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 *cgrp, struct task_struct *leader) * 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; goto out_free_group_list; } @@ -2057,7 +2057,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) } while_each_thread(leader, tsk); /* remember the number of threads in the array for later. */ group_size = i; - rcu_read_unlock(); + read_unlock(&tasklist_lock); /* * step 1: check that we can legitimately attach to the cgroup.