[PATCH 3.15 42/84] dm io: fix a race condition in the wake up code for sync_io

Greg Kroah-Hartman
2014-07-15T23:39:11Z

From: Joe Thornber <thornber@redhat.com>

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@ucloud.cn>
Signed-off-by: Joe Thornber <thornber@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/dm-io.c | 22 ++++++++--------------
1 file changed, 8 insertions(+), 14 deletions(-)

--- 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, uns
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;
@@ -387,6 +388,7 @@ static int sync_io(struct dm_io_client *
*/
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);
@@ -395,7 +397,7 @@ static int sync_io(struct dm_io_client *

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;
@@ -403,15 +405,7 @@ static int sync_io(struct dm_io_client *

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;
@@ -434,7 +428,7 @@ static int async_io(struct dm_io_client
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;