From: Oren Laadan <orenl@xxxxxxxxxxx>
If prepare_descendants() is walking a tree and one of the tasks is
forking, one of two bads can happen. If the child doesn't inherit the
->ctx, it breaks the assumption that the entire subtree is prepared.
If the child inherits the ->ctx, it will have one without having taken
a reference.
This patch closed this race by explicitly getting and referencing the
->ctx for a child process should the parent have one, atomically under
the tasklist_lock.
Signed-off-by: Oren Laadan <orenl@xxxxxxxxxxxxxxx>
---
kernel/fork.c | 11 ++++++++---
1 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index 9f13d7b..57118e4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -62,6 +62,7 @@
#include <linux/fs_struct.h>
#include <linux/magic.h>
#include <linux/perf_counter.h>
+#include <linux/checkpoint.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -1148,9 +1149,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
INIT_LIST_HEAD(&p->pi_state_list);
p->pi_state_cache = NULL;
#endif
-#ifdef CONFIG_CHECKPOINT
- p->checkpoint_ctx = NULL;
-#endif
/*
* sigaltstack should be cleared when sharing the same VM
*/
@@ -1188,6 +1186,13 @@ static struct task_struct *copy_process(unsigned long clone_flags,
/* Need tasklist lock for parent etc handling! */
write_lock_irq(&tasklist_lock);
+#ifdef CONFIG_CHECKPOINT
+ /* If parent is restarting, child should be too */
+ if (unlikely(current->checkpoint_ctx)) {
+ p->checkpoint_ctx = current->checkpoint_ctx;
+ ckpt_ctx_get(p->checkpoint_ctx);
+ }
+#endif
/*
* The task hasn't been attached yet, so its cpus_allowed mask will
* not be changed, nor will its assigned CPU.
--
1.6.0.4
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