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: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
drivers/md/dm-core.h | 4 ++
drivers/md/dm-crypt.c | 1
drivers/md/dm.c | 60 ++++++++++++++++++++++++++++++++++++++++++
include/linux/device-mapper.h | 5 +++
4 files changed, 70 insertions(+)
Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c 2021-02-10 15:04:53.000000000 +0100
+++ linux-2.6/drivers/md/dm.c 2021-02-10 21:22:21.000000000 +0100
@@ -148,6 +148,16 @@ EXPORT_SYMBOL_GPL(dm_bio_get_target_bio_
#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.
*/
@@ -969,6 +979,11 @@ void disable_write_zeroes(struct mapped_
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;
@@ -1019,6 +1034,11 @@ 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);
}
@@ -1252,6 +1272,22 @@ void dm_accept_partial_bio(struct bio *b
}
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;
@@ -1271,6 +1307,14 @@ static blk_qc_t __map_bio(struct dm_targ
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:
@@ -1281,10 +1325,18 @@ static blk_qc_t __map_bio(struct dm_targ
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;
@@ -1747,6 +1799,7 @@ static void cleanup_mapped_device(struct
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);
}
@@ -1814,6 +1867,10 @@ static struct mapped_device *alloc_dev(i
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;
@@ -3097,6 +3154,9 @@ MODULE_PARM_DESC(reserved_bio_based_ios,
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, "The number of swap I/Os in flight");
+
MODULE_DESCRIPTION(DM_NAME " driver");
MODULE_AUTHOR("Joe Thornber <dm-devel@xxxxxxxxxx>");
MODULE_LICENSE("GPL");
Index: linux-2.6/drivers/md/dm-core.h
===================================================================
--- linux-2.6.orig/drivers/md/dm-core.h 2021-02-10 15:04:53.000000000 +0100
+++ linux-2.6/drivers/md/dm-core.h 2021-02-10 21:07:08.000000000 +0100
@@ -102,6 +102,10 @@ 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 */
Index: linux-2.6/drivers/md/dm-crypt.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-crypt.c 2021-01-28 17:33:30.000000000 +0100
+++ linux-2.6/drivers/md/dm-crypt.c 2021-02-10 21:06:33.000000000 +0100
@@ -3324,6 +3324,7 @@ static int crypt_ctr(struct dm_target *t
wake_up_process(cc->write_thread);
ti->num_flush_bios = 1;
+ ti->limit_swap_bios = true;
return 0;
Index: linux-2.6/include/linux/device-mapper.h
===================================================================
--- linux-2.6.orig/include/linux/device-mapper.h 2020-11-25 13:40:44.000000000 +0100
+++ linux-2.6/include/linux/device-mapper.h 2021-02-10 21:06:24.000000000 +0100
@@ -325,6 +325,11 @@ 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);
--
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