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[PATCH] Don't crash if we are self-checkpointing with a child [message #41821] Tue, 22 February 2011 19:16
Dan Smith is currently offline  Dan Smith
Messages: 3
Registered: February 2011
Junior Member
From: *
If we are doing a self-checkpoint, we will not be frozen and the
get_freezer_task() will return NULL. If we have children, then
may_checkpoint_task() will attempt to make sure that they are in the
same cgroup as the freezer task, which will attempt to lock a NULL
task pointer (and thus go boom).

This patch just inserts a check before in_same_cgroup_freezer() call
to make sure we have a freezer task. The existing check is aimed to
determine if a task is not frozen alongside the root, so this addition
catches the case where it is impossible.

Signed-off-by: Dan Smith <>
kernel/checkpoint/checkpoint.c | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/checkpoint/checkpoint.c b/kernel/checkpoint/checkpoint.c
index 0f46acf..33f53e9 100644
--- a/kernel/checkpoint/checkpoint.c
+++ b/kernel/checkpoint/checkpoint.c
@@ -262,8 +262,12 @@ static int may_checkpoint_task(struct ckpt_ctx *ctx, struct task_struct *t)
if (t->exit_state)
return 0;

- /* verify that all tasks belongs to same freezer cgroup */
- if (t != current && !in_same_cgroup_freezer(t, ctx->root_freezer)) {
+ /*
+ * verify that we have a freezer cgroup and that all tasks
+ * belong to the same one
+ */
+ if (t != current && (!ctx->root_freezer ||
+ !in_same_cgroup_freezer(t, ctx->root_freezer))) {
_ckpt_err(ctx, -EBUSY, "%(T)Not frozen or wrong cgroup\n");
return -EBUSY;

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