[PATCH v3 3/3] aio_free_ring: don't do page_count(NULL)

[Oleg Nesterov <oleg@redhat.com>]

aio_free_ring() can actually see the NULL page in ->ring_pages[],
this can happen if aio_setup_ring() fails.

And in this case page_count(ctx->ring_pages[i]) can OOPS.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
---
 fs/aio.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index d63a889..b9947ed 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -292,12 +292,12 @@ static void aio_free_ring(struct kioctx *ctx)
 	put_aio_ring_file(ctx);
 
 	for (i = 0; i < ctx->nr_pages; i++) {
-		struct page *page;
-		pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i,
-				page_count(ctx->ring_pages[i]));
-		page = ctx->ring_pages[i];
+		struct page *page = ctx->ring_pages[i];
 		if (!page)
 			continue;
+
+		pr_debug("pid(%d) [%d] page->count=%d\n",
+				current->pid, i, page_count(page));
 		ctx->ring_pages[i] = NULL;
 		put_page(page);
 	}
-- 
1.5.5.1