Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=3c90e6e99b08f01d5684a3a07cceae6a543e4fa8
Commit: 3c90e6e99b08f01d5684a3a07cceae6a543e4fa8
Parent: 502d26b524d8980f3ed80d9aec398e85671a8160
Author: Srivatsa Vaddagiri <[EMAIL PROTECTED]>
AuthorDate: Fri Nov 9 22:39:39 2007 +0100
Committer: Ingo Molnar <[EMAIL PROTECTED]>
CommitDate: Fri Nov 9 22:39:39 2007 +0100
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 <[EMAIL PROTECTED]>
Signed-off-by: Srivatsa Vaddagiri <[EMAIL PROTECTED]>
Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
---
kernel/fork.c | 6 +++---
kernel/sched_fair.c | 3 ++-
2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index 28a7401..8ca1a14 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. */
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 6c36147..d3c0307 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1067,8 +1067,9 @@ static void task_new_fair(struct rq *rq, struct
task_struct *p)
update_curr(cfs_rq);
place_entity(cfs_rq, se, 1);
+ /* 'curr' will be NULL if the child belongs to a different group */
if (sysctl_sched_child_runs_first && this_cpu == task_cpu(p) &&
- curr->vruntime < se->vruntime) {
+ curr && curr->vruntime < se->vruntime) {
/*
* Upon rescheduling, sched_class::put_prev_task() will place
* 'current' within the tree based on its new key value.
-
To unsubscribe from this list: send the line "unsubscribe git-commits-head" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
