Oren Laadan [orenl@xxxxxxxxxxxxxxx] wrote:
| Add a 'users' count to objhash items, and, for a !CHECKPOINT_SUBTREE
| checkpoint, return an error code if the actual objects' counts are
| higher, indicating leaks (references to the objects from a task not
| being checkpointed). Of course, by this time most of the checkpoint
| image has been written out to disk, so this is purely advisory. But
| then, it's probably naive to argue that anything more than an advisory
| 'this went wrong' error code is useful.
|
| The comparison of the objhash user counts to object refcounts as a
| basis for checking for leaks comes from Alexey's OpenVZ-based c/r
| patchset.
|
| Signed-off-by: Oren Laadan <orenl@xxxxxxxxxxxxxxx>
| ---
| checkpoint/checkpoint.c | 8 +++
| checkpoint/memory.c | 2 +
| checkpoint/objhash.c | 108 +++++++++++++++++++++++++++++++++++++++----
| include/linux/checkpoint.h | 2 +
| 4 files changed, 110 insertions(+), 10 deletions(-)
|
| diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
| index 4319976..32a0a8e 100644
| --- a/checkpoint/checkpoint.c
| +++ b/checkpoint/checkpoint.c
| @@ -498,6 +498,14 @@ int do_checkpoint(struct ckpt_ctx *ctx, pid_t pid)
| if (ret < 0)
| goto out;
|
| + if (!(ctx->flags & CHECKPOINT_SUBTREE)) {
| + /* verify that all objects are contained (no leaks) */
| + if (!ckpt_obj_contained(ctx)) {
| + ret = -EBUSY;
| + goto out;
| + }
| + }
| +
| /* on success, return (unique) checkpoint identifier */
| ctx->crid = atomic_inc_return(&ctx_count);
| ret = ctx->crid;
| diff --git a/checkpoint/memory.c b/checkpoint/memory.c
| index 7637c1e..5ae2b41 100644
| --- a/checkpoint/memory.c
| +++ b/checkpoint/memory.c
| @@ -687,6 +687,8 @@ static int do_checkpoint_mm(struct ckpt_ctx *ctx, struct mm_struct *mm)
| ret = exe_objref;
| goto out;
| }
| + /* account for all references through vma/exe_file */
| + ckpt_obj_users_inc(ctx, mm->exe_file, mm->num_exe_file_vmas);
Do we really need to add num_exe_file_vmas here ?
A quick look at all callers for added_exe_file_vma() seems to show that
those callers also do a get_file().
Anyway, when I try to C/R a simple process tree, I get -EBUSY because
ckpt_obj_contained() finds a ref-count mismatch for the executable file.
I suspect the above increment of 'num_exe_file_vmas' is causing
'obj->users' to exceed the value returned by the file's ->ref_users().
Or, when incrementing by 'num_exe_file_vmas', should we also call
obj_file_grab() ('num_exe_file_vmas' times) to keep the ref counts
in sync ?
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