The patch titled
cgroups: more safe tasklist locking in cgroup_attach_proc
has been added to the -mm tree. Its filename is
cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc.patch
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------------------------------------------------------
Subject: cgroups: more safe tasklist locking in cgroup_attach_proc
From: Ben Blum <bblum@xxxxxxxxxxxxxx>
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 <bblum@xxxxxxxxxxxxxx>
Acked-by: Paul Menage <paul@xxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Neil Brown <neilb@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/cgroup.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff -puN kernel/cgroup.c~cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc kernel/cgroup.c
--- a/kernel/cgroup.c~cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc
+++ a/kernel/cgroup.c
@@ -2027,7 +2027,7 @@ int cgroup_attach_proc(struct cgroup *cg
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 *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;
goto out_free_group_list;
}
@@ -2057,7 +2057,7 @@ int cgroup_attach_proc(struct cgroup *cg
} 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.
_
Patches currently in -mm which might be from bblum@xxxxxxxxxxxxxx are
cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc.patch
cgroups-fix-ordering-of-calls-in-cgroup_attach_proc.patch
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