On Fri, Dec 20, 2013 at 5:02 AM, Linus Torvalds
<torva...@linux-foundation.org> wrote:
>
> Why not just get rid of the idiotic get_user_pages() crap then?
> Something like the attached patch?
>
> Totally untested, but at least it makes *some* amount of sense.
Ok, that can't work, since the ring_pages[] allocation happens later.
So that part needs to be moved up, and it needs to initialize
'nr_pages'.
So here's the same patch, but with stuff moved around a bit, and the
"oops, couldn't create page" part fixed.
Bit it's still totally and entirely untested.
Linus
fs/aio.c | 54 +++++++++++++++++++++---------------------------------
1 file changed, 21 insertions(+), 33 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index 6efb7f6cb22e..3e857e98fb87 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -347,6 +347,20 @@ static int aio_setup_ring(struct kioctx *ctx)
return -EAGAIN;
}
+ ctx->aio_ring_file = file;
+ nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring))
+ / sizeof(struct io_event);
+
+ ctx->ring_pages = ctx->internal_pages;
+ if (nr_pages > AIO_RING_PAGES) {
+ ctx->ring_pages = kcalloc(nr_pages, sizeof(struct page *),
+ GFP_KERNEL);
+ if (!ctx->ring_pages) {
+ put_aio_ring_file(ctx);
+ return -ENOMEM;
+ }
+ }
+
for (i = 0; i < nr_pages; i++) {
struct page *page;
page = find_or_create_page(file->f_inode->i_mapping,
@@ -358,19 +372,14 @@ static int aio_setup_ring(struct kioctx *ctx)
SetPageUptodate(page);
SetPageDirty(page);
unlock_page(page);
+
+ ctx->ring_pages[i] = page;
}
- ctx->aio_ring_file = file;
- nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring))
- / sizeof(struct io_event);
+ ctx->nr_pages = i;
- ctx->ring_pages = ctx->internal_pages;
- if (nr_pages > AIO_RING_PAGES) {
- ctx->ring_pages = kcalloc(nr_pages, sizeof(struct page *),
- GFP_KERNEL);
- if (!ctx->ring_pages) {
- put_aio_ring_file(ctx);
- return -ENOMEM;
- }
+ if (unlikely(i != nr_pages)) {
+ aio_free_ring(ctx);
+ return -EAGAIN;
}
ctx->mmap_size = nr_pages * PAGE_SIZE;
@@ -380,8 +389,8 @@ static int aio_setup_ring(struct kioctx *ctx)
ctx->mmap_base = do_mmap_pgoff(ctx->aio_ring_file, 0, ctx->mmap_size,
PROT_READ | PROT_WRITE,
MAP_SHARED | MAP_POPULATE, 0, &populate);
+ up_write(&mm->mmap_sem);
if (IS_ERR((void *)ctx->mmap_base)) {
- up_write(&mm->mmap_sem);
ctx->mmap_size = 0;
aio_free_ring(ctx);
return -EAGAIN;
@@ -389,27 +398,6 @@ static int aio_setup_ring(struct kioctx *ctx)
pr_debug("mmap address: 0x%08lx\n", ctx->mmap_base);
- /* We must do this while still holding mmap_sem for write, as we
- * need to be protected against userspace attempting to mremap()
- * or munmap() the ring buffer.
- */
- ctx->nr_pages = get_user_pages(current, mm, ctx->mmap_base, nr_pages,
- 1, 0, ctx->ring_pages, NULL);
-
- /* Dropping the reference here is safe as the page cache will hold
- * onto the pages for us. It is also required so that page migration
- * can unmap the pages and get the right reference count.
- */
- for (i = 0; i < ctx->nr_pages; i++)
- put_page(ctx->ring_pages[i]);
-
- up_write(&mm->mmap_sem);
-
- if (unlikely(ctx->nr_pages != nr_pages)) {
- aio_free_ring(ctx);
- return -EAGAIN;
- }
-
ctx->user_id = ctx->mmap_base;
ctx->nr_events = nr_events; /* trusted copy */
