diff options
| author | Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com> | 2007-11-09 22:39:39 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2007-11-09 22:39:39 +0100 |
| commit | 3c90e6e99b08f01d5684a3a07cceae6a543e4fa8 (patch) | |
| tree | 2432814cfe4891e4c99945fbe09e6b59d6df49f3 /kernel/fork.c | |
| parent | 502d26b524d8980f3ed80d9aec398e85671a8160 (diff) | |
sched: fix copy_namespace() <-> sched_fork() dependency in do_fork
Sukadev Bhattiprolu reported a kernel crash with control groups.
There are couple of problems discovered by Suka's test:
- The test requires the cgroup filesystem to be mounted with
atleast the cpu and ns options (i.e both namespace and cpu
controllers are active in the same hierarchy).
# mkdir /dev/cpuctl
# mount -t cgroup -ocpu,ns none cpuctl
(or simply)
# mount -t cgroup none cpuctl -> Will activate all controllers
in same hierarchy.
- The test invokes clone() with CLONE_NEWNS set. This causes a a new child
to be created, also a new group (do_fork->copy_namespaces->ns_cgroup_clone->
cgroup_clone) and the child is attached to the new group (cgroup_clone->
attach_task->sched_move_task). At this point in time, the child's scheduler
related fields are uninitialized (including its on_rq field, which it has
inherited from parent). As a result sched_move_task thinks its on
runqueue, when it isn't.
As a solution to this problem, I moved sched_fork() call, which
initializes scheduler related fields on a new task, before
copy_namespaces(). I am not sure though whether moving up will
cause other side-effects. Do you see any issue?
- The second problem exposed by this test is that task_new_fair()
assumes that parent and child will be part of the same group (which
needn't be as this test shows). As a result, cfs_rq->curr can be NULL
for the child.
The solution is to test for curr pointer being NULL in
task_new_fair().
With the patch below, I could run ns_exec() fine w/o a crash.
Reported-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/fork.c')
| -rw-r--r-- | kernel/fork.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/fork.c b/kernel/fork.c index 28a74015198..8ca1a14cdc8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1123,6 +1123,9 @@ static struct task_struct *copy_process(unsigned long clone_flags, p->blocked_on = NULL; /* not blocked yet */ #endif + /* Perform scheduler related setup. Assign this task to a CPU. */ + sched_fork(p, clone_flags); + if ((retval = security_task_alloc(p))) goto bad_fork_cleanup_policy; if ((retval = audit_alloc(p))) @@ -1212,9 +1215,6 @@ static struct task_struct *copy_process(unsigned long clone_flags, INIT_LIST_HEAD(&p->ptrace_children); INIT_LIST_HEAD(&p->ptrace_list); - /* Perform scheduler related setup. Assign this task to a CPU. */ - sched_fork(p, clone_flags); - /* Now that the task is set up, run cgroup callbacks if * necessary. We need to run them before the task is visible * on the tasklist. */ |