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 Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ 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 -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html