[PATCH v5 3/3] aio_free_ring: don't do page_count(NULL)

[Oleg Nesterov]

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 <o...@redhat.com>
Reviewed-by: Jeff Moyer <jmo...@redhat.com>
---
 fs/aio.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 4a360be..9bc1335 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

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