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Message-Id: <20100401150956.4f6821c2.kamezawa.hiroyu@jp.fujitsu.com>
Date: Thu, 1 Apr 2010 15:09:56 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Matt Mackall <mpm@...enic.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
San Mehat <san@...gle.com>, linux-kernel@...r.kernel.org,
Brian Swetland <swetland@...gle.com>,
Dave Hansen <haveblue@...ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
n-horiguchi@...jp.nec.com
Subject: Re: [PATCH] proc: pagemap: Hold mmap_sem during page walk
On Thu, 1 Apr 2010 15:05:38 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
memset(&mss, 0, sizeof mss);
> > mss.vma = vma;
> > - if (vma->vm_mm && !is_vm_hugetlb_page(vma))
> > + if (vma->vm_mm && !is_vm_hugetlb_page(vma)) {
> > + down_read(&vma->vm_mm->mmap_sem);
> > walk_page_range(vma->vm_start, vma->vm_end, &smaps_walk);
> > + up_read(&vma->vm_mm->mmap_sem);
> > + }
>
> m_start already take mmap_sem. then I don't think this part is necessary.
>
Right.
<snip>
> > -
> > - uaddr = (unsigned long)buf & PAGE_MASK;
> > - uend = (unsigned long)(buf + count);
> > - pagecount = (PAGE_ALIGN(uend) - uaddr) / PAGE_SIZE;
> > - ret = 0;
> > - if (pagecount == 0)
> > + pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
> > + pm.buffer = kmalloc(pm.len, GFP_KERNEL);
>
> In /proc interface, GFP_TEMPORARY is recommened rather than GFP_KERNEL.
> it help to prevent unnecessary external fragmentation.
>
Ok.
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
In initial design, walk_page_range() was designed just for walking page table and
it didn't require mmap_sem. Now, find_vma() etc.. are used in walk_page_range()
and we need mmap_sem around it.
This patch adds mmap_sem around walk_page_range().
Because /proc/<pid>/pagemap's callback routine use put_user(), we have to get
rid of it to do sane fix.
Changelog:
- removed unnecessary change in smaps.
- use GFP_TEMPORARY instead of GFP_KERNEL
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
fs/proc/task_mmu.c | 86 ++++++++++++++++++++++-------------------------------
1 file changed, 36 insertions(+), 50 deletions(-)
Index: linux-2.6.34-rc3/fs/proc/task_mmu.c
===================================================================
--- linux-2.6.34-rc3.orig/fs/proc/task_mmu.c
+++ linux-2.6.34-rc3/fs/proc/task_mmu.c
@@ -406,6 +406,7 @@ static int show_smap(struct seq_file *m,
memset(&mss, 0, sizeof mss);
mss.vma = vma;
+ /* mmap_sem is held in m_start */
if (vma->vm_mm && !is_vm_hugetlb_page(vma))
walk_page_range(vma->vm_start, vma->vm_end, &smaps_walk);
@@ -552,7 +553,8 @@ const struct file_operations proc_clear_
};
struct pagemapread {
- u64 __user *out, *end;
+ int pos, len;
+ u64 *buffer;
};
#define PM_ENTRY_BYTES sizeof(u64)
@@ -575,10 +577,8 @@ struct pagemapread {
static int add_to_pagemap(unsigned long addr, u64 pfn,
struct pagemapread *pm)
{
- if (put_user(pfn, pm->out))
- return -EFAULT;
- pm->out++;
- if (pm->out >= pm->end)
+ pm->buffer[pm->pos++] = pfn;
+ if (pm->pos >= pm->len)
return PM_END_OF_BUFFER;
return 0;
}
@@ -720,21 +720,20 @@ static int pagemap_hugetlb_range(pte_t *
* determine which areas of memory are actually mapped and llseek to
* skip over unmapped regions.
*/
+#define PAGEMAP_WALK_SIZE (PMD_SIZE)
static ssize_t pagemap_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
- struct page **pages, *page;
- unsigned long uaddr, uend;
struct mm_struct *mm;
struct pagemapread pm;
- int pagecount;
int ret = -ESRCH;
struct mm_walk pagemap_walk = {};
unsigned long src;
unsigned long svpfn;
unsigned long start_vaddr;
unsigned long end_vaddr;
+ int copied = 0;
if (!task)
goto out;
@@ -757,34 +756,10 @@ static ssize_t pagemap_read(struct file
if (!mm)
goto out_task;
-
- uaddr = (unsigned long)buf & PAGE_MASK;
- uend = (unsigned long)(buf + count);
- pagecount = (PAGE_ALIGN(uend) - uaddr) / PAGE_SIZE;
- ret = 0;
- if (pagecount == 0)
+ pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
+ pm.buffer = kmalloc(pm.len, GFP_TEMPORARY);
+ if (!pm.buffer)
goto out_mm;
- pages = kcalloc(pagecount, sizeof(struct page *), GFP_KERNEL);
- ret = -ENOMEM;
- if (!pages)
- goto out_mm;
-
- down_read(¤t->mm->mmap_sem);
- ret = get_user_pages(current, current->mm, uaddr, pagecount,
- 1, 0, pages, NULL);
- up_read(¤t->mm->mmap_sem);
-
- if (ret < 0)
- goto out_free;
-
- if (ret != pagecount) {
- pagecount = ret;
- ret = -EFAULT;
- goto out_pages;
- }
-
- pm.out = (u64 __user *)buf;
- pm.end = (u64 __user *)(buf + count);
pagemap_walk.pmd_entry = pagemap_pte_range;
pagemap_walk.pte_hole = pagemap_pte_hole;
@@ -807,23 +782,34 @@ static ssize_t pagemap_read(struct file
* user buffer is tracked in "pm", and the walk
* will stop when we hit the end of the buffer.
*/
- ret = walk_page_range(start_vaddr, end_vaddr, &pagemap_walk);
- if (ret == PM_END_OF_BUFFER)
- ret = 0;
- /* don't need mmap_sem for these, but this looks cleaner */
- *ppos += (char __user *)pm.out - buf;
- if (!ret)
- ret = (char __user *)pm.out - buf;
-
-out_pages:
- for (; pagecount; pagecount--) {
- page = pages[pagecount-1];
- if (!PageReserved(page))
- SetPageDirty(page);
- page_cache_release(page);
+ while (count && (start_vaddr < end_vaddr)) {
+ int len;
+ unsigned long end;
+
+ pm.pos = 0;
+ start_vaddr += PAGEMAP_WALK_SIZE;
+ end = start_vaddr + PAGEMAP_WALK_SIZE;
+ down_read(&mm->mmap_sem);
+ ret = walk_page_range(start_vaddr, end, &pagemap_walk);
+ up_read(&mm->mmap_sem);
+
+ len = PM_ENTRY_BYTES * pm.pos;
+ if (len > count)
+ len = count;
+ if (copy_to_user((char __user *)buf, pm.buffer, len) < 0) {
+ ret = -EFAULT;
+ goto out_free;
+ }
+ copied += len;
+ buf += len;
+ count -= len;
}
+ *ppos += copied;
+ if (!ret || ret == PM_END_OF_BUFFER)
+ ret = copied;
+
out_free:
- kfree(pages);
+ kfree(pm.buffer);
out_mm:
mmput(mm);
out_task:
--
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