Messages in this thread Patch in this message | | | Date | Thu, 13 Oct 2011 20:31:15 -0400 | From | Ben Blum <> | Subject | [PATCH 1/2] cgroups: use sighand lock instead of tasklist_lock in cgroup_attach_proc |
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Use sighand lock instead of tasklist_lock in cgroup_attach_proc.
From: Ben Blum <bblum@andrew.cmu.edu>
Signed-off-by: Ben Blum <bblum@andrew.cmu.edu> --- kernel/cgroup.c | 27 +++++++++++++-------------- 1 files changed, 13 insertions(+), 14 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 893fc3d..32fb4c8 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2003,6 +2003,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) /* threadgroup list cursor and array */ struct task_struct *tsk; struct flex_array *group; + unsigned long flags; /* * we need to make sure we have css_sets for all the tasks we're * going to move -before- we actually start moving them, so that in @@ -2029,20 +2030,18 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) if (retval) goto out_free_group_list; - /* prevent changes to the threadgroup list while we take a snapshot. */ - read_lock(&tasklist_lock); - if (!thread_group_leader(leader)) { - /* - * a race with de_thread from another thread's exec() may strip - * us of our leadership, making while_each_thread unsafe to use - * on this task. if this happens, there is no choice but to - * throw this task away and try again (from cgroup_procs_write); - * this is "double-double-toil-and-trouble-check locking". - */ - read_unlock(&tasklist_lock); - retval = -EAGAIN; + /* prevent changes to the threadgroup list while we take a snapshot. + * If the leader exits, its links on the thread_group list become + * invalid. One way this can happen is if a sub-thread does exec() when + * de_thread() calls release_task(leader) (and leader->sighand gets set + * to NULL, in which case lock_task_sighand will fail). Since in that + * case the threadgroup is still around, cgroup_procs_write should try + * again (finding the new leader), which EAGAIN indicates here. This is + * double-double-toil-and-trouble-check locking". */ + retval = -EAGAIN; + if (!lock_task_sighand(leader, &flags)) goto out_free_group_list; - } + /* take a reference on each task in the group to go in the array. */ tsk = leader; i = 0; @@ -2058,9 +2057,9 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) BUG_ON(retval != 0); i++; } while_each_thread(leader, tsk); + unlock_task_sighand(leader, &flags); /* remember the number of threads in the array for later. */ group_size = i; - read_unlock(&tasklist_lock); /* * step 1: check that we can legitimately attach to the cgroup.
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