Oren Laadan [orenl@xxxxxxxxxxxxxxx] wrote:
|
|
| Sukadev Bhattiprolu wrote:
| > 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().
|
| Each vma whose file is the same as mm->exe_file causes the refcount
| of that file to increase by 2: once by vma->vm_file, and once via
| added_exe_file_vma(). The c/r code calls ckpt_obj_checkpoint() only
| once, thus once one obj_file_grab() for that file. The code above
| accounts for the missing count.
If the executable is shared between a parent and child (as in fork()/dup_mm)
do we still need to account for the 'added_exe_file_vma()' in the child
process ?
i.e I can trace a call to added_exe_file_vma() when loading/mmaping a biniary.
But I can't trace a call to added_exe_file_vma() during fork()/dup_mm()).
Here is how I can account for the 16 in the obj->users :-)
Parent:
do_checkpoint_mm: +2 = 2 (first time/obj_new())
num_exe_vmas: +2 = 4
filemap_checkpoint: +1 = 5 (text section)
filemap_checkpoint: +1 = 6 (data section)
Child:
do_checkpoint_mm: +1 = 7
num_exe_file_vmas: +2 = 9
filemap_checkpoint: +1 = 10 (text section)
filemap_checkpoint: +1 = 11 (data section)
Grand child:
do_checkpoint_mm: +1 = 12
num_exe_file_vmas: +2 = 14
filemap_checkpoint: +1 = 15 (text section)
filemap_checkpoint: +1 = 16 (data section)
Even if we were to drop the num_exe_file_vmas for the child and
grand-child, we would be off by 2 :-(
As of now, I can account for 9 of the 10 found in file->f_count.
Parent:
load_a.out/do_mmap: +2 = 2 (text)
load_aout/do_mmap(): +2 = 4 (data)
Child:
dup_mm()/dup_mmap(): +1 = 5 (text)
dup_mm()/dup_mmap(): +1 = 6 (data)
Grand Child:
dup_mm()/dup_mmap(): +1 = 7 (text)
dup_mm()/dup_mmap(): +1 = 8 (data)
Checkpoint/Objhash:
obj_new/obj_file_grab: +1 = 9
Another question is regarding the obj->users = 2 in obj_new():
- one of this reference is for the get_file() in obj_file_grab()
called near the end of obj_new() right ?
- where can I find the other get_file() ?
(again with reference to the file the three process are executing, ptree2)
Thanks,
Sukadev
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