From: Mikulas Patocka mpatocka@redhat.com
commit a666e5c05e7c4aaabb2c5d58117b0946803d03d2 upstream.
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@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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(+)
--- a/drivers/md/dm-core.h +++ b/drivers/md/dm-core.h @@ -110,6 +110,10 @@ struct mapped_device { /* zero-length flush that will be cloned and submitted to targets */ struct bio flush_bio;
+ int swap_bios; + struct semaphore swap_bios_semaphore; + struct mutex swap_bios_lock; + struct dm_stats stats;
struct kthread_worker kworker; --- a/drivers/md/dm-crypt.c +++ b/drivers/md/dm-crypt.c @@ -2852,6 +2852,7 @@ 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;
--- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -146,6 +146,16 @@ 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. */ @@ -935,6 +945,11 @@ 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; @@ -972,6 +987,11 @@ 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); } @@ -1250,6 +1270,22 @@ void dm_remap_zone_report(struct dm_targ } EXPORT_SYMBOL_GPL(dm_remap_zone_report);
+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; @@ -1270,6 +1306,14 @@ 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: @@ -1284,10 +1328,18 @@ static blk_qc_t __map_bio(struct dm_targ ret = generic_make_request(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; @@ -1859,6 +1911,7 @@ 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); } @@ -1933,6 +1986,10 @@ static struct mapped_device *alloc_dev(i init_completion(&md->kobj_holder.completion); md->kworker_task = NULL;
+ 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; @@ -3228,6 +3285,9 @@ 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, "Maximum allowed inflight swap IOs"); + MODULE_DESCRIPTION(DM_NAME " driver"); MODULE_AUTHOR("Joe Thornber dm-devel@redhat.com"); MODULE_LICENSE("GPL"); --- a/include/linux/device-mapper.h +++ b/include/linux/device-mapper.h @@ -315,6 +315,11 @@ struct dm_target { * on max_io_len boundary. */ bool split_discard_bios:1; + + /* + * Set if we need to limit the number of in-flight bios when swapping. + */ + bool limit_swap_bios:1; };
/* Each target can link one of these into the table */