[PATCH 2/2] aio: fix the confliction of read events and migrating ring page

[Gu Zheng <guz.fnst@cn.fujitsu.com>]

Since we do not have additional protection on the page at the read events
side, so it is possible that the read of the page takes place after the
page has been freed and allocated to another part of the kernel. This
would result in the read returning invalid information.
So here we add a mutex pair before putting old page when migrating page
success to fix the confliction of reading events and migrating page.

Reported-by: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
---
 fs/aio.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 88ad40c..e353085 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -319,6 +319,9 @@ static int aio_migratepage(struct address_space *mapping, struct page *new,
 	ctx->ring_pages[old->index] = new;
 	spin_unlock_irqrestore(&ctx->completion_lock, flags);
 
+	/* Ensure read event is completed before putting old page */
+	mutex_lock(&ctx->ring_lock);
+	mutex_unlock(&ctx->ring_lock);
 	put_page(old);
 
 	return rc;
-- 
1.7.7