Btw, should we first check if page returned by radix_tree_deref_slot is NULL?
diff --git a/mm/filemap.c b/mm/filemap.c
index 1bc12a9..c129ee5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1745,6 +1745,8 @@ void filemap_map_pages(struct vm_area_struct
*vma, struct vm_fault *vmf)
break;
repeat:
page = radix_tree_deref_slot(slot);
+ if (unlikely(!page))
+ continue;
if (radix_tree_exception(page)) {
if (radix_tree_deref_retry(page))
Best wishes,
--
Ning Qu (曲宁) | Software Engineer | quning@xxxxxxxxxx | +1-408-418-6066
On Fri, Feb 28, 2014 at 5:20 PM, Hugh Dickins <hughd@xxxxxxxxxx> wrote:
> On Fri, 28 Feb 2014, Ning Qu wrote:
>
>> In shmem/tmpfs, we also use the generic filemap_map_pages,
>> seems the additional checking is not worth a separate version
>> of map_pages for it.
>>
>> Signed-off-by: Ning Qu <quning@xxxxxxxxxx>
>> ---
>> mm/shmem.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 1f18c9d..2ea4e89 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -2783,6 +2783,7 @@ static const struct super_operations shmem_ops = {
>>
>> static const struct vm_operations_struct shmem_vm_ops = {
>> .fault = shmem_fault,
>> + .map_pages = filemap_map_pages,
>> #ifdef CONFIG_NUMA
>> .set_policy = shmem_set_policy,
>> .get_policy = shmem_get_policy,
>> --
>
> (There's no need for a 0/1, all the info should go into the one patch.)
>
> I expect this will prove to be a very sensible and adequate patch,
> thank you: it probably wouldn't be worth more effort to give shmem
> anything special of its own, and filemap_map_pages() is already
> (almost) coping with exceptional entries.
>
> But I can't Ack it until I've tested it some more, won't be able to
> do so until Sunday; and even then some doubt, since this and Kirill's
> are built upon mmotm/next, which after a while gives me spinlock
> lockups under load these days, yet to be investigated.
>
> "almost" above because, Kirill, even without Ning's extension to
> shmem, your filemap_map_page() soon crashes on an exceptional entry:
>
> Don't try to dereference an exceptional entry.
>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
>
> --- mmotm+kirill/mm/filemap.c 2014-02-28 15:17:50.984019060 -0800
> +++ linux/mm/filemap.c 2014-02-28 16:38:04.976633308 -0800
> @@ -2084,7 +2084,7 @@ repeat:
> if (radix_tree_deref_retry(page))
> break;
> else
> - goto next;
> + continue;
> }
>
> if (!page_cache_get_speculative(page))
--
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