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Message-ID: <531D4E23.4060505@cn.fujitsu.com>
Date: Mon, 10 Mar 2014 13:31:15 +0800
From: Tang Chen <tangchen@...fujitsu.com>
To: viro@...iv.linux.org.uk, bcrl@...ck.org, jmoyer@...hat.com,
kosaki.motohiro@...il.com, kosaki.motohiro@...fujitsu.com,
isimatu.yasuaki@...fujitsu.com, guz.fnst@...fujitsu.com
CC: linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
linux-kernel@...r.kernel.org, Miao Xie <miaox@...fujitsu.com>
Subject: [V2 PATCH 2/2] aio, mem-hotplug: Add memory barrier to aio ring page
migration.
When doing aio ring page migration, we migrated the page, and update
ctx->ring_pages[]. Like the following:
aio_migratepage()
|-> migrate_page_copy(new, old)
| ...... /* Need barrier here */
|-> ctx->ring_pages[idx] = new
Actually, we need a memory barrier between these two operations.
Otherwise, if ctx->ring_pages[] is updated before memory copy due to
the compiler optimization, other processes may have an opportunity
to access to the not fully initialized new ring page.
So add a wmb and rmb to synchronize them.
v2:
change smp_rmb() to smp_read_barrier_depends(). Thanks Miao.
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
---
fs/aio.c | 14 ++++++++++++++
1 files changed, 14 insertions(+), 0 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index dc70246..4133ba9 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -327,6 +327,14 @@ static int aio_migratepage(struct address_space
*mapping, struct page *new,
pgoff_t idx;
spin_lock_irqsave(&ctx->completion_lock, flags);
migrate_page_copy(new, old);
+
+ /*
+ * Ensure memory copy is finished before updating
+ * ctx->ring_pages[]. Otherwise other processes may access to
+ * new ring pages which are not fully initialized.
+ */
+ smp_wmb();
+
idx = old->index;
if (idx < (pgoff_t)ctx->nr_pages) {
/* And only do the move if things haven't changed */
@@ -1069,6 +1077,12 @@ static long aio_read_events_ring(struct kioctx *ctx,
page = ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE];
pos %= AIO_EVENTS_PER_PAGE;
+ /*
+ * Ensure that the page's data was copied from old one by
+ * aio_migratepage().
+ */
+ smp_read_barrier_depends();
+
ev = kmap(page);
copy_ret = copy_to_user(event + ret, ev + pos,
sizeof(*ev) * avail);
--
1.7.7
--
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