any reason why you want to reference the entire ->fs instead of, as I
suggested, make a *copy* of ->fs->root and then reference its contents ?
Dave Hansen wrote:
> The existing ctx->vfsroot is dangerous. We take it from
> the root task via: ctx->root_task->fs->root and don't take
> a ref on the 'fs' in there. We also take a ref on the
> fs.root which is worthless.
>
> So, replace ctx->vfsroot with a reference to the 'fs'
> instead. This gives us easy access to fs.root later on,
> and also lets us do proper refcounting.
>
> This, of course, eventually needs to be done per-process
> but this should at least remove a potential oops.
>
> ---
>
> linux-2.6.git-dave/checkpoint/checkpoint.c | 7 ++-----
> linux-2.6.git-dave/checkpoint/ckpt_file.c | 2 +-
> linux-2.6.git-dave/checkpoint/ckpt_mem.c | 2 +-
> linux-2.6.git-dave/checkpoint/sys.c | 4 ++--
> linux-2.6.git-dave/include/linux/checkpoint.h | 2 +-
> 5 files changed, 7 insertions(+), 10 deletions(-)
>
> diff -puN checkpoint/checkpoint.c~fix-cr_ctx_checkpoint-locking
> checkpoint/checkpoint.c
> --- linux-2.6.git/checkpoint/checkpoint.c~fix-cr_ctx_checkpoint-locking
> 2008-12-02 10:21:52.000000000 -0800
> +++ linux-2.6.git-dave/checkpoint/checkpoint.c 2008-12-02
> 10:21:52.000000000 -0800
> @@ -511,12 +511,9 @@ static int cr_ctx_checkpoint(struct cr_c
> * assume checkpointer is in container's root vfs
> * FIXME: this works for now, but will change with real containers
> */
> - task_lock(ctx->root_task);
> - ctx->vfsroot = &ctx->root_task->fs->root;
> - task_unlock(ctx->root_task);
> - if (!ctx->vfsroot)
> + ctx->fs = get_fs_struct(ctx->root_task);
> + if (!ctx->fs)
> return -EAGAIN;
> - path_get(ctx->vfsroot);
>
> return 0;
> }
> diff -puN checkpoint/ckpt_file.c~fix-cr_ctx_checkpoint-locking
> checkpoint/ckpt_file.c
> --- linux-2.6.git/checkpoint/ckpt_file.c~fix-cr_ctx_checkpoint-locking
> 2008-12-02 10:21:52.000000000 -0800
> +++ linux-2.6.git-dave/checkpoint/ckpt_file.c 2008-12-02 10:46:56.000000000
> -0800
> @@ -117,7 +117,7 @@ static int cr_write_fd_data(struct cr_ct
> if (ret < 0)
> return ret;
>
> - return cr_write_fname(ctx, &file->f_path, ctx->vfsroot);
> + return cr_write_fname(ctx, &file->f_path, &ctx->fs.root);
> }
>
> /**
> diff -puN checkpoint/ckpt_mem.c~fix-cr_ctx_checkpoint-locking
> checkpoint/ckpt_mem.c
> --- linux-2.6.git/checkpoint/ckpt_mem.c~fix-cr_ctx_checkpoint-locking
> 2008-12-02 10:21:52.000000000 -0800
> +++ linux-2.6.git-dave/checkpoint/ckpt_mem.c 2008-12-02 10:21:52.000000000
> -0800
> @@ -436,7 +436,7 @@ static int cr_write_vma(struct cr_ctx *c
>
> /* save the file name, if relevant */
> if (vma->vm_file) {
> - ret = cr_write_fname(ctx, &vma->vm_file->f_path, ctx->vfsroot);
> + ret = cr_write_fname(ctx, &vma->vm_file->f_path, &ctx->fs.root);
> if (ret < 0)
> return ret;
> }
> diff -puN checkpoint/sys.c~fix-cr_ctx_checkpoint-locking checkpoint/sys.c
> --- linux-2.6.git/checkpoint/sys.c~fix-cr_ctx_checkpoint-locking
> 2008-12-02 10:21:52.000000000 -0800
> +++ linux-2.6.git-dave/checkpoint/sys.c 2008-12-02 10:21:52.000000000
> -0800
> @@ -152,8 +152,8 @@ static void cr_ctx_free(struct cr_ctx *c
>
> kfree(ctx->hbuf);
>
> - if (ctx->vfsroot)
> - path_put(ctx->vfsroot);
> + if (ctx->fs)
> + put_fs_struct(ctx->fs);
>
> cr_pgarr_free(ctx);
> cr_objhash_free(ctx);
> diff -puN include/linux/checkpoint.h~fix-cr_ctx_checkpoint-locking
> include/linux/checkpoint.h
> --- linux-2.6.git/include/linux/checkpoint.h~fix-cr_ctx_checkpoint-locking
> 2008-12-02 10:21:52.000000000 -0800
> +++ linux-2.6.git-dave/include/linux/checkpoint.h 2008-12-02
> 10:21:52.000000000 -0800
> @@ -41,7 +41,7 @@ struct cr_ctx {
>
> struct list_head pgarr_list; /* page array to dump VMA contents */
>
> - struct path *vfsroot; /* container root (FIXME) */
> + struct fs_struct *fs; /* container root/pwd (FIXME) */
>
> /* [multi-process checkpoint] */
> struct task_struct **tasks_arr; /* array of all tasks [checkpoint] */
> _
>
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