On Wed, Apr 21, 2010 at 07:46:15PM +0200, Andrea Arcangeli wrote:
> On Wed, Apr 21, 2010 at 11:24:24AM -0400, Rik van Riel wrote:
> > On 04/21/2010 06:27 AM, Dan Carpenter wrote:
> > > The follow_page() function can potentially return -EFAULT so I added
> > > checks for this.
> > >
> > > Also I silenced an uninitialized variable warning on my version of gcc
> > > (version 4.3.2).
> > >
> > > Signed-off-by: Dan Carpenter<error27@xxxxxxxxx>
> >
> > Acked-by: Rik van Riel <riel@xxxxxxxxxx>
>
> while (!(page = follow_page(vma, start, foll_flags)))
> {
>
> gup only checks for null, so when exactly is follow_page going to
> return -EFAULT? It's not immediately clear.
Check below that loop. If it returns non-null, the first check is
whether it IS_ERR().
How about the below?
Hannes
---
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: mm: document follow_page()
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
mm/memory.c | 13 +++++++++++--
1 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 833952d..119b7cc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1227,8 +1227,17 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
}
EXPORT_SYMBOL_GPL(zap_vma_ptes);
-/*
- * Do a quick page-table lookup for a single page.
+/**
+ * follow_page - look up a page descriptor from a user-virtual address
+ * @vma: vm_area_struct mapping @address
+ * @address: virtual address to look up
+ * @flags: flags modifying lookup behaviour
+ *
+ * @flags can have FOLL_ flags set, defined in <linux/mm.h>
+ *
+ * Returns the mapped (struct page *), %NULL if no mapping exists, or
+ * an error pointer if there is a mapping to something not represented
+ * by a page descriptor (see also vm_normal_page()).
*/
struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
unsigned int flags)
--
1.7.0.2
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