[3.13.y.z extended stable] Patch "dm io: fix a race condition in the wake up code for sync_io" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    dm io: fix a race condition in the wake up code for sync_io

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 7a505a6f586558e1a5d655824d97f2357a582a29 Mon Sep 17 00:00:00 2001
From: Joe Thornber <thornber at redhat.com>
Date: Fri, 27 Jun 2014 15:29:04 -0400
Subject: dm io: fix a race condition in the wake up code for sync_io

commit 10f1d5d111e8aed46a0f1179faf9a3cf422f689e upstream.

There's a race condition between the atomic_dec_and_test(&io->count)
in dec_count() and the waking of the sync_io() thread.  If the thread
is spuriously woken immediately after the decrement it may exit,
making the on stack io struct invalid, yet the dec_count could still
be using it.

Fix this race by using a completion in sync_io() and dec_count().

Reported-by: Minfei Huang <huangminfei at ucloud.cn>
Signed-off-by: Joe Thornber <thornber at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Acked-by: Mikulas Patocka <mpatocka at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/dm-io.c | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 2a20986..e60c2ea 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -10,6 +10,7 @@
 #include <linux/device-mapper.h>

 #include <linux/bio.h>
+#include <linux/completion.h>
 #include <linux/mempool.h>
 #include <linux/module.h>
 #include <linux/sched.h>
@@ -32,7 +33,7 @@ struct dm_io_client {
 struct io {
 	unsigned long error_bits;
 	atomic_t count;
-	struct task_struct *sleeper;
+	struct completion *wait;
 	struct dm_io_client *client;
 	io_notify_fn callback;
 	void *context;
@@ -121,8 +122,8 @@ static void dec_count(struct io *io, unsigned int region, int error)
 			invalidate_kernel_vmap_range(io->vma_invalidate_address,
 						     io->vma_invalidate_size);

-		if (io->sleeper)
-			wake_up_process(io->sleeper);
+		if (io->wait)
+			complete(io->wait);

 		else {
 			unsigned long r = io->error_bits;
@@ -385,6 +386,7 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,
 	 */
 	volatile char io_[sizeof(struct io) + __alignof__(struct io) - 1];
 	struct io *io = (struct io *)PTR_ALIGN(&io_, __alignof__(struct io));
+	DECLARE_COMPLETION_ONSTACK(wait);

 	if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
 		WARN_ON(1);
@@ -393,7 +395,7 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,

 	io->error_bits = 0;
 	atomic_set(&io->count, 1); /* see dispatch_io() */
-	io->sleeper = current;
+	io->wait = &wait;
 	io->client = client;

 	io->vma_invalidate_address = dp->vma_invalidate_address;
@@ -401,15 +403,7 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,

 	dispatch_io(rw, num_regions, where, dp, io, 1);

-	while (1) {
-		set_current_state(TASK_UNINTERRUPTIBLE);
-
-		if (!atomic_read(&io->count))
-			break;
-
-		io_schedule();
-	}
-	set_current_state(TASK_RUNNING);
+	wait_for_completion_io(&wait);

 	if (error_bits)
 		*error_bits = io->error_bits;
@@ -432,7 +426,7 @@ static int async_io(struct dm_io_client *client, unsigned int num_regions,
 	io = mempool_alloc(client->pool, GFP_NOIO);
 	io->error_bits = 0;
 	atomic_set(&io->count, 1); /* see dispatch_io() */
-	io->sleeper = NULL;
+	io->wait = NULL;
 	io->client = client;
 	io->callback = fn;
 	io->context = context;
--
1.9.1