proc: pagemap: Hold mmap_sem during page walk

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: 2010/Apr/2
 - fixed start_vaddr and end overflow
Changelog: 2010/Apr/1
 - fixed start_vaddr calculation
 - removed unnecessary cast.
 - removed unnecessary change in smaps.
 - use GFP_TEMPORARY instead of GFP_KERNEL

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: San Mehat <san@google.com>
Cc: Brian Swetland <swetland@google.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
[ Fixed kmalloc failure return code as per Matt ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 38 insertions, 49 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 183f8ff5f400..096273984c3b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -406,6 +406,7 @@ static int show_smap(struct seq_file *m, void *v)
 
         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_refs_operations = {
 };
 
 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 *pte, unsigned long addr,
  * 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;
@@ -757,35 +756,12 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
         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)
-                goto out_mm;
-        pages = kcalloc(pagecount, sizeof(struct page *), GFP_KERNEL);
+        pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
+        pm.buffer = kmalloc(pm.len, GFP_TEMPORARY);
         ret = -ENOMEM;
-        if (!pages)
+        if (!pm.buffer)
                 goto out_mm;
 
-        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);
-
-        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;
         pagemap_walk.hugetlb_entry = pagemap_hugetlb_range;
@@ -807,23 +783,36 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
          * 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);
+        ret = 0;
+        while (count && (start_vaddr < end_vaddr)) {
+                int len;
+                unsigned long end;
+
+                pm.pos = 0;
+                end = start_vaddr + PAGEMAP_WALK_SIZE;
+                /* overflow ? */
+                if (end < start_vaddr || end > end_vaddr)
+                        end = end_vaddr;
+                down_read(&mm->mmap_sem);
+                ret = walk_page_range(start_vaddr, end, &pagemap_walk);
+                up_read(&mm->mmap_sem);
+                start_vaddr = end;
+
+                len = min(count, PM_ENTRY_BYTES * pm.pos);
+                if (copy_to_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: