[RFC][PATCH 2/2] CR: handle a single task with private memory maps
Serge E. Hallyn
serue at us.ibm.com
Wed Jul 30 09:52:49 PDT 2008
This list is getting on my nerves. Louis, I'm sorry the threading
is going to get messed up.
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Date: Wed, 30 Jul 2008 18:15:35 +0200
From: Louis Rilling <Louis.Rilling at kerlabs.com>
To: Oren Laadan <orenl at cs.columbia.edu>
Cc: Linux Containers <containers at lists.linux-foundation.org>
Subject: Re: [RFC][PATCH 2/2] CR: handle a single task with private memory
maps
Reply-To: Louis.Rilling at kerlabs.com
Hi Oren,
On Tue, Jul 29, 2008 at 11:27:17PM -0400, Oren Laadan wrote:
>
> Expand the template sys_checkpoint and sys_restart to be able to dump
> and restore a single task. The task's address space may consist of only
> private, simple vma's - anonymous or file-mapped.
>
> This big patch adds a mechanism to transfer data between kernel or user
> space to and from the file given by the caller (sys.c), alloc/setup/free
> of the checkpoint/restart context (sys.c), output wrappers and basic
> checkpoint handling (checkpoint.c), memory dump (ckpt_mem.c), input
> wrappers and basic restart handling (restart.c), and finally the memory
> restore (rstr_mem.c).
This looks globally clean to me, but I'm sure that others will have stronger
arguments against or in favor of it.
Just a few comments inline, in case it helps.
[...]
> diff --git a/ckpt/checkpoint.c b/ckpt/checkpoint.c
> new file mode 100644
> index 0000000..1698a35
> --- /dev/null
> +++ b/ckpt/checkpoint.c
[...]
> +/* dump the task_struct of a given task */
> +static int cr_write_task_struct(struct cr_ctx *ctx, struct task_struct *t)
> +{
> + struct cr_hdr h;
> + struct cr_hdr_task *hh = ctx->tbuf;
> +
> + h.type = CR_HDR_TASK;
> + h.len = sizeof(*hh);
> + h.id = ctx->pid;
> +
> + hh->state = t->state;
> + hh->exit_state = t->exit_state;
> + hh->exit_code = t->exit_code;
> + hh->exit_signal = t->exit_signal;
> +
> + hh->pid = t->pid;
> + hh->tgid = t->tgid;
IIRC, it is assumed that pid and tgid will be restored before actually calling
sys_restart(), eg by giving the proper pid and clone flags to a variant of
do_fork(). So, maybe these ids are useless here and should be put earlier in the
checkpoint header (see also the matching comment below in cr_read_task_struct()).
[...]
> diff --git a/ckpt/ckpt_mem.c b/ckpt/ckpt_mem.c
> new file mode 100644
> index 0000000..12caad0
> --- /dev/null
> +++ b/ckpt/ckpt_mem.c
[...]
> +/**
> + * cr_vma_fill_pgarr - fill a page-array with addr/page tuples for a vma
> + * @ctx - checkpoint context
> + * @pgarr - page-array to fill
> + * @vma - vma to scan
> + * @start - start address (updated)
> + */
> +static int cr_vma_fill_pgarr(struct cr_ctx *ctx, struct cr_pgarr *pgarr,
> + struct vm_area_struct *vma, unsigned long *start)
> +{
> + unsigned long end = vma->vm_end;
> + unsigned long addr = *start;
> + struct page **pagep;
> + unsigned long *addrp;
> + int cow, nr, ret = 0;
> +
> + nr = pgarr->nleft;
> + pagep = &pgarr->pages[pgarr->nused];
> + addrp = &pgarr->addrs[pgarr->nused];
> + cow = !!vma->vm_file;
> +
> + while (addr < end) {
> + struct page *page;
> +
> + /* simplified version of get_user_pages(): already have vma,
> + * only need FOLL_TOUCH, and (for now) ignore fault stats */
> +
> + cond_resched();
> + while (!(page = follow_page(vma, addr, FOLL_TOUCH))) {
> + ret = handle_mm_fault(vma->vm_mm, vma, addr, 0);
> + if (ret & VM_FAULT_ERROR) {
> + if (ret & VM_FAULT_OOM)
> + ret = -ENOMEM;
> + else if (ret & VM_FAULT_SIGBUS)
> + ret = -EFAULT;
> + else
> + BUG();
> + break;
> + }
> + cond_resched();
> + }
I guess that 'ret' should be checked somewhere after this loop.
> +
> + if (IS_ERR(page)) {
> + ret = PTR_ERR(page);
> + break;
> + }
> +
> + if (page == ZERO_PAGE(0))
> + page = NULL; /* zero page: ignore */
> + else if (cow && page_mapping(page) != NULL)
> + page = NULL; /* clean cow: ignore */
> + else {
> + get_page(page);
> + *(addrp++) = addr;
> + *(pagep++) = page;
> + if (--nr == 0) {
> + addr += PAGE_SIZE;
> + break;
> + }
> + }
> +
> + addr += PAGE_SIZE;
> + }
> +
> + if (unlikely(ret < 0)) {
> + nr = pgarr->nleft - nr;
> + while (nr--)
> + page_cache_release(*(--pagep));
> + return ret;
> + }
> +
> + *start = addr;
> + return (pgarr->nleft - nr);
> +}
> +
[...]
> +int cr_write_mm(struct cr_ctx *ctx, struct task_struct *t)
> +{
> + struct cr_hdr h;
> + struct cr_hdr_mm *hh = ctx->tbuf;
> + struct mm_struct *mm;
> + struct vm_area_struct *vma;
> + int ret;
> +
> + h.type = CR_HDR_MM;
> + h.len = sizeof(*hh);
> + h.id = ctx->pid;
> +
> + mm = get_task_mm(t);
> +
> + hh->tag = 1; /* non-zero will mean first time encounter */
> +
> + hh->start_code = mm->start_code;
> + hh->end_code = mm->end_code;
> + hh->start_data = mm->start_data;
> + hh->end_data = mm->end_data;
> + hh->start_brk = mm->start_brk;
> + hh->brk = mm->brk;
> + hh->start_stack = mm->start_stack;
> + hh->arg_start = mm->arg_start;
> + hh->arg_end = mm->arg_end;
> + hh->env_start = mm->env_start;
> + hh->env_end = mm->env_end;
> +
> + hh->map_count = mm->map_count;
Some fields above should also be protected with mmap_sem, like ->brk,
->map_count, and possibly others (I'm not a memory expert though).
> +
> + /* FIX: need also mm->flags */
> +
> + ret = cr_write_obj(ctx, &h, hh);
> + if (ret < 0)
> + goto out;
> +
> + /* write the vma's */
> + down_read(&mm->mmap_sem);
> + for (vma = mm->mmap; vma; vma = vma->vm_next) {
> + if ((ret = cr_write_vma(ctx, vma)) < 0)
> + break;
> + }
> + up_read(&mm->mmap_sem);
> +
> + if (ret < 0)
> + goto out;
> +
> + ret = cr_write_mm_context(ctx, mm);
> +
> + out:
> + mmput(mm);
> + return ret;
> +}
[...]
> diff --git a/ckpt/restart.c b/ckpt/restart.c
> new file mode 100644
> index 0000000..9f52851
> --- /dev/null
> +++ b/ckpt/restart.c
[...]
> +/* read the task_struct into the current task */
> +static int cr_read_task_struct(struct cr_ctx *ctx)
> +{
> + struct cr_hdr_task *hh = cr_hbuf_get(ctx, sizeof(*hh));
> + struct task_struct *t = current;
> + int ret;
> +
> + ret = cr_read_obj_type(ctx, hh, sizeof(*hh), CR_HDR_TASK);
> + if (ret < 0)
> + return ret;
> +
> + /* for now, only restore t->comm */
+ /* current should already have correct pid and tgid */
> + if (hh->task_comm_len < 0 || hh->task_comm_len > TASK_COMM_LEN)
> + return -EINVAL;
> +
> + memset(t->comm, 0, TASK_COMM_LEN);
> + memcpy(t->comm, hh->comm, hh->task_comm_len);
> +
> + cr_hbuf_put(ctx, sizeof(*hh));
> + return 0;
> +}
> +
Louis
--
Dr Louis Rilling Kerlabs
Skype: louis.rilling Batiment Germanium
Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
http://www.kerlabs.com/ 35700 Rennes
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