Commit 10f1d5d1 authored by Joe Thornber's avatar Joe Thornber Committed by Mike Snitzer
Browse files

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



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: default avatarMinfei Huang <huangminfei@ucloud.cn>
Signed-off-by: default avatarJoe Thornber <thornber@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Acked-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
parent bf14299f

drivers/md/dm-io.c

+8 −14
Original line number Diff line number Diff line
@@ -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;
@@ -387,6 +388,7 @@ 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);
@@ -395,7 +397,7 @@ 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;
@@ -403,15 +405,7 @@ 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;
@@ -434,7 +428,7 @@ 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;

CRA Git | Maintained and supported by SUSTech CRA and CCSE