Re: [RFC][PATCH 1/9] /proc/pid/pagemap update

[Matt Mackall <mpm@selenic.com>]

On Tue, Aug 21, 2007 at 01:42:48PM -0700, Dave Hansen wrote:
> 
> This is a series of patches to update /proc/pid/pagemap,
> to simplify the code, and fix bugs which caused userspace
> memory corruption.
> 
> Since it is just in -mm, we should probably roll all of
> these together and just update it all at once, or send
> a simple drop-on replacement patch.  These patches are
> all here mostly to help with review.
> 
> Matt, if you're OK with these, do you mind if I send
> the update into -mm, or would you like to do it?

Hmmm, is the below working for you? I was having trouble with it.

> --
> From: Matt Mackall <mpm@selenic.com>
> 
> On Mon, Aug 06, 2007 at 01:44:19AM -0500, Dave Boutcher wrote:
> > 
> > Matt, this patch set replaces the two patches I sent earlier and
> > contains additional fixes.  I've done some reasonably rigorous testing
> > on x86_64, but not on a 32 bit arch.  I'm pretty sure this isn't worse
> > than what's in mm right now, which has some user-space corruption and
> > a nasty infinite kernel loop. YMMV.
> 
> Dave, here's my current work-in-progress patch to deal with a couple
> locking issues, primarily a possible deadlock on the mm semaphore that
> can occur if someone unmaps the target buffer while we're walking the
> tree. It currently hangs on my box and I haven't had any free cycles
> to finish debugging it, but you might want to take a peek at it.
> 
> Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
> ---
> 
>  lxc-dave/fs/proc/task_mmu.c |  121 ++++++++++++++++++++------------------------
>  1 file changed, 55 insertions(+), 66 deletions(-)
> 
> diff -puN fs/proc/task_mmu.c~Re-_PATCH_0_3_proc_pid_pagemap_fixes fs/proc/task_mmu.c
> --- lxc/fs/proc/task_mmu.c~Re-_PATCH_0_3_proc_pid_pagemap_fixes	2007-08-21 13:30:50.000000000 -0700
> +++ lxc-dave/fs/proc/task_mmu.c	2007-08-21 13:30:50.000000000 -0700
> @@ -501,37 +501,21 @@ const struct file_operations proc_clear_
>  };
>  
>  struct pagemapread {
> -	struct mm_struct *mm;
>  	unsigned long next;
> -	unsigned long *buf;
> -	pte_t *ptebuf;
>  	unsigned long pos;
>  	size_t count;
>  	int index;
> -	char __user *out;
> +	unsigned long __user *out;
>  };
>  
> -static int flush_pagemap(struct pagemapread *pm)
> -{
> -	int n = min(pm->count, pm->index * sizeof(unsigned long));
> -	if (copy_to_user(pm->out, pm->buf, n))
> -		return -EFAULT;
> -	pm->out += n;
> -	pm->pos += n;
> -	pm->count -= n;
> -	pm->index = 0;
> -	cond_resched();
> -	return 0;
> -}
> -
>  static int add_to_pagemap(unsigned long addr, unsigned long pfn,
>  			  struct pagemapread *pm)
>  {
> -	pm->buf[pm->index++] = pfn;
> +	__put_user(pfn, pm->out);
> +	pm->out++;
> +	pm->pos += sizeof(unsigned long);
> +	pm->count -= sizeof(unsigned long);
>  	pm->next = addr + PAGE_SIZE;
> -	if (pm->index * sizeof(unsigned long) >= PAGE_SIZE ||
> -	    pm->index * sizeof(unsigned long) >= pm->count)
> -		return flush_pagemap(pm);
>  	return 0;
>  }
>  
> @@ -543,14 +527,6 @@ static int pagemap_pte_range(pmd_t *pmd,
>  	int err;
>  
>  	pte = pte_offset_map(pmd, addr);
> -
> -#ifdef CONFIG_HIGHPTE
> -	/* copy PTE directory to temporary buffer and unmap it */
> -	memcpy(pm->ptebuf, pte, PAGE_ALIGN((unsigned long)pte) - (unsigned long)pte);
> -	pte_unmap(pte);
> -	pte = pm->ptebuf;
> -#endif
> -
>  	for (; addr != end; pte++, addr += PAGE_SIZE) {
>  		if (addr < pm->next)
>  			continue;
> @@ -560,11 +536,12 @@ static int pagemap_pte_range(pmd_t *pmd,
>  			err = add_to_pagemap(addr, pte_pfn(*pte), pm);
>  		if (err)
>  			return err;
> +		if (pm->count == 0)
> +			break;
>  	}
> -
> -#ifndef CONFIG_HIGHPTE
>  	pte_unmap(pte - 1);
> -#endif
> +
> +	cond_resched();
>  
>  	return 0;
>  }
> @@ -573,7 +550,7 @@ static int pagemap_fill(struct pagemapre
>  {
>  	int ret;
>  
> -	while (pm->next != end) {
> +	while (pm->next != end && pm->count > 0) {
>  		ret = add_to_pagemap(pm->next, -1UL, pm);
>  		if (ret)
>  			return ret;
> @@ -608,15 +585,16 @@ static ssize_t pagemap_read(struct file 
>  {
>  	struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
>  	unsigned long src = *ppos;
> -	unsigned long *page;
> -	unsigned long addr, end, vend, svpfn, evpfn;
> +	struct page **pages, *page;
> +	unsigned long addr, end, vend, svpfn, evpfn, uaddr, uend;
>  	struct mm_struct *mm;
>  	struct vm_area_struct *vma;
>  	struct pagemapread pm;
> +	int pagecount;
>  	int ret = -ESRCH;
>  
>  	if (!task)
> -		goto out_no_task;
> +		goto out;
>  
>  	ret = -EACCES;
>  	if (!ptrace_may_attach(task))
> @@ -628,39 +606,43 @@ static ssize_t pagemap_read(struct file 
>  	if ((svpfn + 1) * sizeof(unsigned long) != src)
>  		goto out;
>  	evpfn = min((src + count) / sizeof(unsigned long) - 1,
> -		    ((~0UL) >> PAGE_SHIFT) + 1);
> +		    ((~0UL) >> PAGE_SHIFT) + 1) - 1;
>  	count = (evpfn - svpfn) * sizeof(unsigned long);
>  	end = PAGE_SIZE * evpfn;
> -
> -	ret = -ENOMEM;
> -	page = kzalloc(PAGE_SIZE, GFP_USER);
> -	if (!page)
> -		goto out;
> -
> -#ifdef CONFIG_HIGHPTE
> -	pm.ptebuf = kzalloc(PAGE_SIZE, GFP_USER);
> -	if (!pm.ptebuf)
> -		goto out_free;
> -#endif
> +	//printk("src %ld svpfn %d evpfn %d count %d\n", src, svpfn, evpfn, count);
>  
>  	ret = 0;
>  	mm = get_task_mm(task);
>  	if (!mm)
> -		goto out_freepte;
> +		goto out;
> +
> +	ret = -ENOMEM;
> +	uaddr = (unsigned long)buf & ~(PAGE_SIZE-1);
> +	uend = (unsigned long)(buf + count);
> +	pagecount = (uend - uaddr + PAGE_SIZE-1) / PAGE_SIZE;
> +	pages = kmalloc(pagecount * sizeof(struct page *), GFP_KERNEL);
> +	if (!pages)
> +		goto out_task;
> +
> +	down_read(&current->mm->mmap_sem);
> +	ret = get_user_pages(current, current->mm, uaddr, pagecount,
> +			     1, 0, pages, NULL);
> +	up_read(&current->mm->mmap_sem);
> +
> +	//printk("%x(%x):%x %d@%ld (%d pages) -> %d\n", uaddr, buf, uend, count, src, pagecount, ret);
> +	if (ret < 0)
> +		goto out_free;
>  
> -	pm.mm = mm;
>  	pm.next = addr;
> -	pm.buf = page;
>  	pm.pos = src;
>  	pm.count = count;
> -	pm.index = 0;
> -	pm.out = buf;
> +	pm.out = (unsigned long __user *)buf;
>  
>  	if (svpfn == -1) {
> -		((char *)page)[0] = (ntohl(1) != 1);
> -		((char *)page)[1] = PAGE_SHIFT;
> -		((char *)page)[2] = sizeof(unsigned long);
> -		((char *)page)[3] = sizeof(unsigned long);
> +		put_user((char)(ntohl(1) != 1), buf);
> +		put_user((char)PAGE_SHIFT, buf + 1);
> +		put_user((char)sizeof(unsigned long), buf + 2);
> +		put_user((char)sizeof(unsigned long), buf + 3);
>  		add_to_pagemap(pm.next, page[0], &pm);
>  	}
>  
> @@ -669,7 +651,8 @@ static ssize_t pagemap_read(struct file 
>  	while (pm.count > 0 && vma) {
>  		if (!ptrace_may_attach(task)) {
>  			ret = -EIO;
> -			goto out_mm;
> +			up_read(&mm->mmap_sem);
> +			goto out_release;
>  		}
>  		vend = min(vma->vm_end - 1, end - 1) + 1;
>  		ret = pagemap_fill(&pm, vend);
> @@ -682,23 +665,29 @@ static ssize_t pagemap_read(struct file 
>  	}
>  	up_read(&mm->mmap_sem);
>  
> +	//printk("before fill at %ld\n", pm.pos);
>  	ret = pagemap_fill(&pm, end);
>  
> +	printk("after fill at %ld\n", pm.pos);
>  	*ppos = pm.pos;
>  	if (!ret)
>  		ret = pm.pos - src;
>  
> -out_mm:
> +out_release:
> +	printk("releasing pages\n");
> +	for (; pagecount; pagecount--) {
> +		page = pages[pagecount-1];
> +		if (!PageReserved(page))
> +			SetPageDirty(page);
> +		page_cache_release(page);
> +	}
>  	mmput(mm);
> -out_freepte:
> -#ifdef CONFIG_HIGHPTE
> -	kfree(pm.ptebuf);
>  out_free:
> -#endif
> -	kfree(page);
> -out:
> +	kfree(pages);
> +out_task:
>  	put_task_struct(task);
> -out_no_task:
> +out:
> +	printk("returning\n");
>  	return ret;
>  }
>  
> _

-- 
Mathematics is the supreme nostalgia of our time.

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