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Message-ID: <20081128105351.GQ28946@ZenIV.linux.org.uk>
Date: Fri, 28 Nov 2008 10:53:51 +0000
From: Al Viro <viro@...IV.linux.org.uk>
To: Oren Laadan <orenl@...columbia.edu>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...l.org>,
containers@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-api@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Serge Hallyn <serue@...ibm.com>,
Dave Hansen <dave@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC v10][PATCH 05/13] Dump memory address space
On Wed, Nov 26, 2008 at 08:04:36PM -0500, Oren Laadan wrote:
> For each VMA, there is a 'struct cr_vma'; if the VMA is file-mapped,
> it will be followed by the file name. Then comes the actual contents,
> in one or more chunk: each chunk begins with a header that specifies
> how many pages it holds, then the virtual addresses of all the dumped
> pages in that chunk, followed by the actual contents of all dumped
> pages. A header with zero number of pages marks the end of the contents.
> Then comes the next VMA and so on.
>
> Changelog[v10]:
> - Acquire dcache_lock around call to __d_path() in cr_fill_name()
>
> Changelog[v9]:
> - Introduce cr_ctx_checkpoint() for checkpoint-specific ctx setup
> - Test if __d_path() changes mnt/dentry (when crossing filesystem
> namespace boundary). for now cr_fill_fname() fails the checkpoint.
>
> Changelog[v7]:
> - Fix argument given to kunmap_atomic() in memory dump/restore
>
> Changelog[v6]:
> - Balance all calls to cr_hbuf_get() with matching cr_hbuf_put()
> (even though it's not really needed)
>
> Changelog[v5]:
> - Improve memory dump code (following Dave Hansen's comments)
> - Change dump format (and code) to allow chunks of <vaddrs, pages>
> instead of one long list of each
> - Fix use of follow_page() to avoid faulting in non-present pages
>
> Changelog[v4]:
> - Use standard list_... for cr_pgarr
>
> Signed-off-by: Oren Laadan <orenl@...columbia.edu>
> Acked-by: Serge Hallyn <serue@...ibm.com>
> Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>
> ---
> arch/x86/include/asm/checkpoint_hdr.h | 5 +
> arch/x86/mm/checkpoint.c | 31 ++
> checkpoint/Makefile | 3 +-
> checkpoint/checkpoint.c | 81 ++++++
> checkpoint/checkpoint_arch.h | 2 +
> checkpoint/checkpoint_mem.h | 41 +++
> checkpoint/ckpt_mem.c | 500 +++++++++++++++++++++++++++++++++
> checkpoint/sys.c | 11 +
> include/linux/checkpoint.h | 12 +
> include/linux/checkpoint_hdr.h | 32 ++
> 10 files changed, 717 insertions(+), 1 deletions(-)
> create mode 100644 checkpoint/checkpoint_mem.h
> create mode 100644 checkpoint/ckpt_mem.c
>
> diff --git a/arch/x86/include/asm/checkpoint_hdr.h b/arch/x86/include/asm/checkpoint_hdr.h
> index 6325062..33f4c70 100644
> --- a/arch/x86/include/asm/checkpoint_hdr.h
> +++ b/arch/x86/include/asm/checkpoint_hdr.h
> @@ -82,4 +82,9 @@ struct cr_hdr_cpu {
> /* thread_xstate contents follow (if used_math) */
> } __attribute__((aligned(8)));
>
> +struct cr_hdr_mm_context {
> + __s16 ldt_entry_size;
> + __s16 nldt;
> +} __attribute__((aligned(8)));
> +
> #endif /* __ASM_X86_CKPT_HDR__H */
> diff --git a/arch/x86/mm/checkpoint.c b/arch/x86/mm/checkpoint.c
> index 8dd6d2d..757936e 100644
> --- a/arch/x86/mm/checkpoint.c
> +++ b/arch/x86/mm/checkpoint.c
> @@ -221,3 +221,34 @@ int cr_write_head_arch(struct cr_ctx *ctx)
>
> return ret;
> }
> +
> +/* dump the mm->context state */
> +int cr_write_mm_context(struct cr_ctx *ctx, struct mm_struct *mm, int parent)
> +{
> + struct cr_hdr h;
> + struct cr_hdr_mm_context *hh = cr_hbuf_get(ctx, sizeof(*hh));
> + int ret;
> +
> + h.type = CR_HDR_MM_CONTEXT;
> + h.len = sizeof(*hh);
> + h.parent = parent;
> +
> + mutex_lock(&mm->context.lock);
> +
> + hh->ldt_entry_size = LDT_ENTRY_SIZE;
> + hh->nldt = mm->context.size;
> +
> + cr_debug("nldt %d\n", hh->nldt);
> +
> + ret = cr_write_obj(ctx, &h, hh);
> + cr_hbuf_put(ctx, sizeof(*hh));
> + if (ret < 0)
> + goto out;
> +
> + ret = cr_kwrite(ctx, mm->context.ldt,
> + mm->context.size * LDT_ENTRY_SIZE);
> +
> + out:
> + mutex_unlock(&mm->context.lock);
> + return ret;
> +}
> diff --git a/checkpoint/Makefile b/checkpoint/Makefile
> index d2df68c..3a0df6d 100644
> --- a/checkpoint/Makefile
> +++ b/checkpoint/Makefile
> @@ -2,4 +2,5 @@
> # Makefile for linux checkpoint/restart.
> #
>
> -obj-$(CONFIG_CHECKPOINT_RESTART) += sys.o checkpoint.o restart.o
> +obj-$(CONFIG_CHECKPOINT_RESTART) += sys.o checkpoint.o restart.o \
> + ckpt_mem.o
> diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
> index 17cc8d2..6a8f810 100644
> --- a/checkpoint/checkpoint.c
> +++ b/checkpoint/checkpoint.c
> @@ -75,6 +75,66 @@ int cr_write_string(struct cr_ctx *ctx, char *str, int len)
> return cr_write_obj(ctx, &h, str);
> }
>
> +/**
> + * cr_fill_fname - return pathname of a given file
> + * @path: path name
> + * @root: relative root
> + * @buf: buffer for pathname
> + * @n: buffer length (in) and pathname length (out)
> + */
> +static char *
> +cr_fill_fname(struct path *path, struct path *root, char *buf, int *n)
> +{
> + struct path tmp = *root;
> + char *fname;
> +
> + BUG_ON(!buf);
> + spin_lock(&dcache_lock);
> + fname = __d_path(path, &tmp, buf, *n);
> + spin_unlock(&dcache_lock);
> + if (!IS_ERR(fname))
> + *n = (buf + (*n) - fname);
> + /*
> + * FIXME: if __d_path() changed these, it must have stepped out of
> + * init's namespace. Since currently we require a unified namespace
> + * within the container: simply fail.
> + */
> + if (tmp.mnt != root->mnt || tmp.dentry != root->dentry)
> + fname = ERR_PTR(-EBADF);
> +
> + return fname;
> +}
> +
> +/**
> + * cr_write_fname - write a file name
> + * @ctx: checkpoint context
> + * @path: path name
> + * @root: relative root
> + */
> +int cr_write_fname(struct cr_ctx *ctx, struct path *path, struct path *root)
> +{
> + struct cr_hdr h;
> + char *buf, *fname;
> + int ret, flen;
> +
> + flen = PATH_MAX;
> + buf = kmalloc(flen, GFP_KERNEL);
> + if (!buf)
> + return -ENOMEM;
> +
> + fname = cr_fill_fname(path, root, buf, &flen);
> + if (!IS_ERR(fname)) {
> + h.type = CR_HDR_FNAME;
> + h.len = flen;
> + h.parent = 0;
> + ret = cr_write_obj(ctx, &h, fname);
> + } else
> + ret = PTR_ERR(fname);
> +
> + kfree(buf);
> + return ret;
> +}
> +
> /* write the checkpoint header */
> static int cr_write_head(struct cr_ctx *ctx)
> {
> @@ -168,6 +228,10 @@ static int cr_write_task(struct cr_ctx *ctx, struct task_struct *t)
> cr_debug("task_struct: ret %d\n", ret);
> if (ret < 0)
> goto out;
> + ret = cr_write_mm(ctx, t);
> + cr_debug("memory: ret %d\n", ret);
> + if (ret < 0)
> + goto out;
> ret = cr_write_thread(ctx, t);
> cr_debug("thread: ret %d\n", ret);
> if (ret < 0)
> @@ -178,10 +242,27 @@ static int cr_write_task(struct cr_ctx *ctx, struct task_struct *t)
> return ret;
> }
>
> +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. 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.
--
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