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 bios, so that the memory consumed by dm-crypt is limited. If we are over the limit, we block in the function crypt_map, so that the caller will not attempt to send more bios. This is similar to request-based drivers - they will also block when the number of bios is over the limit. Signed-off-by: Mikulas Patocka <[email protected]> Cc: [email protected] Index: linux-2.6/drivers/md/dm-crypt.c =================================================================== --- linux-2.6.orig/drivers/md/dm-crypt.c +++ linux-2.6/drivers/md/dm-crypt.c @@ -214,16 +214,21 @@ struct crypt_config { mempool_t page_pool; struct bio_set bs; + + struct semaphore bio_limit; struct mutex bio_alloc_lock; u8 *authenc_key; /* space for keys in authenc() format (if used) */ u8 key[]; }; +#define MAX_BIOS 4096 #define MIN_IOS 64 #define MAX_TAG_SIZE 480 #define POOL_ENTRY_SIZE 512 +static int bio_limit = MAX_BIOS; + static DEFINE_SPINLOCK(dm_crypt_clients_lock); static unsigned dm_crypt_clients_n = 0; static volatile unsigned long dm_crypt_pages_per_client; @@ -1713,6 +1718,7 @@ static void crypt_dec_pending(struct dm_ kfree(io->integrity_metadata); base_bio->bi_status = error; + up(&cc->bio_limit); bio_endio(base_bio); } @@ -3106,6 +3112,7 @@ static int crypt_ctr(struct dm_target *t goto bad; } + sema_init(&cc->bio_limit, bio_limit); mutex_init(&cc->bio_alloc_lock); ret = -EINVAL; @@ -3234,6 +3241,8 @@ static int crypt_map(struct dm_target *t if (unlikely(bio->bi_iter.bi_size & (cc->sector_size - 1))) return DM_MAPIO_KILL; + down(&cc->bio_limit); + io = dm_per_bio_data(bio, cc->per_bio_data_size); crypt_io_init(io, cc, bio, dm_target_offset(ti, bio->bi_iter.bi_sector)); @@ -3461,6 +3470,9 @@ static void __exit dm_crypt_exit(void) module_init(dm_crypt_init); module_exit(dm_crypt_exit); +module_param_named(max_bios_in_flight, bio_limit, int, S_IRUGO | S_IWUSR); +MODULE_PARM_DESC(max_bios_in_flight, "maximum number of bios in flight"); + MODULE_AUTHOR("Jana Saout <[email protected]>"); MODULE_DESCRIPTION(DM_NAME " target for transparent encryption / decryption"); MODULE_LICENSE("GPL"); -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
