[Update v2 PATCH 2/2] aio, mem-hotplug: Add memory barrier to aio ring page migration.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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.

Signed-off-by: Tang Chen <tangchen@xxxxxxxxxxxxxx>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
---
v2: change smp_rmb() to smp_read_barrier_depends(). Thanks Miao.
---
 fs/aio.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/aio.c b/fs/aio.c
index 50c089c..98c7f2d 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 */
@@ -1074,6 +1082,12 @@ 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);

--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux