Commit a666e5c0 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
Browse files

dm: fix deadlock when swapping to encrypted device 



The system would deadlock when swapping to a dm-crypt device. The reason
is that for each incoming write bio, dm-crypt allocates memory that holds
encrypted data. These excessive allocations exhaust all the memory and the
result is either deadlock or OOM trigger.

This patch limits the number of in-flight swap bios, so that the memory
consumed by dm-crypt is limited. The limit is enforced if the target set
the "limit_swap_bios" variable and if the bio has REQ_SWAP set.

Non-swap bios are not affected becuase taking the semaphore would cause
performance degradation.

This is similar to request-based drivers - they will also block when the
number of requests is over the limit.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent e3290b94

drivers/md/dm-core.h

+4 −0
Original line number Diff line number Diff line
@@ -103,6 +103,10 @@ struct mapped_device { 
	/* kobject and completion */

	struct dm_kobject_holder kobj_holder;



	int swap_bios;

	struct semaphore swap_bios_semaphore;

	struct mutex swap_bios_lock;



	struct dm_stats stats;



	/* for blk-mq request-based DM support */

drivers/md/dm-crypt.c

+1 −0
Original line number Diff line number Diff line
@@ -3342,6 +3342,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv) 
	wake_up_process(cc->write_thread);



	ti->num_flush_bios = 1;

	ti->limit_swap_bios = true;



	return 0;

drivers/md/dm.c

+60 −0
Original line number Diff line number Diff line
@@ -153,6 +153,16 @@ EXPORT_SYMBOL_GPL(dm_bio_get_target_bio_nr); 
#define DM_NUMA_NODE NUMA_NO_NODE

static int dm_numa_node = DM_NUMA_NODE;



#define DEFAULT_SWAP_BIOS	(8 * 1048576 / PAGE_SIZE)

static int swap_bios = DEFAULT_SWAP_BIOS;

static int get_swap_bios(void)

{

	int latch = READ_ONCE(swap_bios);

	if (unlikely(latch <= 0))

		latch = DEFAULT_SWAP_BIOS;

	return latch;

}



/*

 * For mempools pre-allocation at the table loading time.

 */
@@ -974,6 +984,11 @@ void disable_write_zeroes(struct mapped_device *md) 
	limits->max_write_zeroes_sectors = 0;

}



static bool swap_bios_limit(struct dm_target *ti, struct bio *bio)

{

	return unlikely((bio->bi_opf & REQ_SWAP) != 0) && unlikely(ti->limit_swap_bios);

}



static void clone_endio(struct bio *bio)

{

	blk_status_t error = bio->bi_status;
@@ -1025,6 +1040,11 @@ static void clone_endio(struct bio *bio) 
		}

	}



	if (unlikely(swap_bios_limit(tio->ti, bio))) {

		struct mapped_device *md = io->md;

		up(&md->swap_bios_semaphore);

	}



	free_tio(tio);

	dec_pending(io, error);

}
@@ -1258,6 +1278,22 @@ void dm_accept_partial_bio(struct bio *bio, unsigned n_sectors) 
}

EXPORT_SYMBOL_GPL(dm_accept_partial_bio);



static noinline void __set_swap_bios_limit(struct mapped_device *md, int latch)

{

	mutex_lock(&md->swap_bios_lock);

	while (latch < md->swap_bios) {

		cond_resched();

		down(&md->swap_bios_semaphore);

		md->swap_bios--;

	}

	while (latch > md->swap_bios) {

		cond_resched();

		up(&md->swap_bios_semaphore);

		md->swap_bios++;

	}

	mutex_unlock(&md->swap_bios_lock);

}



static blk_qc_t __map_bio(struct dm_target_io *tio)

{

	int r;
@@ -1277,6 +1313,14 @@ static blk_qc_t __map_bio(struct dm_target_io *tio) 
	atomic_inc(&io->io_count);

	sector = clone->bi_iter.bi_sector;



	if (unlikely(swap_bios_limit(ti, clone))) {

		struct mapped_device *md = io->md;

		int latch = get_swap_bios();

		if (unlikely(latch != md->swap_bios))

			__set_swap_bios_limit(md, latch);

		down(&md->swap_bios_semaphore);

	}



	r = ti->type->map(ti, clone);

	switch (r) {

	case DM_MAPIO_SUBMITTED:
@@ -1287,10 +1331,18 @@ static blk_qc_t __map_bio(struct dm_target_io *tio) 
		ret = submit_bio_noacct(clone);

		break;

	case DM_MAPIO_KILL:

		if (unlikely(swap_bios_limit(ti, clone))) {

			struct mapped_device *md = io->md;

			up(&md->swap_bios_semaphore);

		}

		free_tio(tio);

		dec_pending(io, BLK_STS_IOERR);

		break;

	case DM_MAPIO_REQUEUE:

		if (unlikely(swap_bios_limit(ti, clone))) {

			struct mapped_device *md = io->md;

			up(&md->swap_bios_semaphore);

		}

		free_tio(tio);

		dec_pending(io, BLK_STS_DM_REQUEUE);

		break;
@@ -1767,6 +1819,7 @@ static void cleanup_mapped_device(struct mapped_device *md) 
	mutex_destroy(&md->suspend_lock);

	mutex_destroy(&md->type_lock);

	mutex_destroy(&md->table_devices_lock);

	mutex_destroy(&md->swap_bios_lock);



	dm_mq_cleanup_mapped_device(md);

}
@@ -1834,6 +1887,10 @@ static struct mapped_device *alloc_dev(int minor) 
	init_waitqueue_head(&md->eventq);

	init_completion(&md->kobj_holder.completion);



	md->swap_bios = get_swap_bios();

	sema_init(&md->swap_bios_semaphore, md->swap_bios);

	mutex_init(&md->swap_bios_lock);



	md->disk->major = _major;

	md->disk->first_minor = minor;

	md->disk->fops = &dm_blk_dops;
@@ -3117,6 +3174,9 @@ MODULE_PARM_DESC(reserved_bio_based_ios, "Reserved IOs in bio-based mempools"); 
module_param(dm_numa_node, int, S_IRUGO | S_IWUSR);

MODULE_PARM_DESC(dm_numa_node, "NUMA node for DM device memory allocations");



module_param(swap_bios, int, S_IRUGO | S_IWUSR);

MODULE_PARM_DESC(swap_bios, "Maximum allowed inflight swap IOs");



MODULE_DESCRIPTION(DM_NAME " driver");

MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");

MODULE_LICENSE("GPL");

include/linux/device-mapper.h

+5 −0
Original line number Diff line number Diff line
@@ -343,6 +343,11 @@ struct dm_target { 
	 * whether or not its underlying devices have support.

	 */

	bool discards_supported:1;



	/*

	 * Set if we need to limit the number of in-flight bios when swapping.

	 */

	bool limit_swap_bios:1;

};



void *dm_per_bio_data(struct bio *bio, size_t data_size);