Messages in this thread | | | Date | Mon, 01 Dec 2008 15:57:09 -0500 | From | Oren Laadan <> | Subject | Re: [RFC v10][PATCH 05/13] Dump memory address space |
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Dave Hansen wrote: > On Fri, 2008-11-28 at 10:53 +0000, Al Viro wrote: >>> +static int cr_ctx_checkpoint(struct cr_ctx *ctx, pid_t pid) >>> +{ >>> + ctx->root_pid = pid; >>> + >>> + /* >>> + * assume checkpointer is in container's root vfs >>> + * FIXME: this works for now, but will change with real containers >>> + */ >>> + ctx->vfsroot = ¤t->fs->root; >>> + path_get(ctx->vfsroot); >> This is going to break as soon as you get another thread doing e.g. chroot(2) >> while you are in there. > > Yeah, we do need at least a read_lock(¤t->fs->lock) to keep people > from chroot()'ing underneath us.
True. (while adapting older and safer code I omitted these tests with no reason).
> >> And it's a really, _really_ bad idea to take a >> pointer to shared object, increment refcount on the current *contents* of >> said object and assume that dropping refcount on the later contents of the >> same will balance out. > > Absolutely. I assume you mean get_fs_struct(current) instead of > path_get().
True.
Should change the type of ctx->vfsroot to not be a pointer, and do:
>>> + ctx->vfsroot = *current->fs->root; >>> + path_get(&ctx->vfsroot);
and adjust accordingly in where the refcount is dropped.
What we need here is a reference point (this will change later when we handle multiple fs-namespaces), which is the path of the "container root". Assuming locking is correct so that current->fs does not change under us, it's enough to get that path and later release that path.
BW, the current->fs is assumed to not change during the checkpoint; if it does, then it's a mis-use of the checkpoint interface, and the resulting behavior is undefined - restart is guaranteed to restore the exact old state even if checkpoint succeeds.
Thanks,
Oren.
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