Hi
I wouldn't do this - these sorts of changes will cause problems when
backporting bugfixes to the stable kernel branches.
Mikulas
On Thu, 17 Jul 2025, Eran Messeri wrote:
> Rename the "in_bh" / "use_bh" fields to indicate the work is done
> in-line, not in the "bottom half" (as a synonym to softirq). In
> certain situations (e.g. dm-verity on top of a loopback device)
> the verification will not be done in a softirq context but in a
> task context.
>
> There are no functional changes to the code.
>
> Signed-off-by: Eran Messeri <er...@google.com>
> ---
> drivers/md/dm-verity-target.c | 85 ++++++++++++++++++++---------------
> drivers/md/dm-verity.h | 10 +++--
> 2 files changed, 55 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index 66a00a8ccb39..be9f6d9fccf4 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -29,7 +29,7 @@
> #define DM_VERITY_ENV_VAR_NAME "DM_VERITY_ERR_BLOCK_NR"
>
> #define DM_VERITY_DEFAULT_PREFETCH_SIZE 262144
> -#define DM_VERITY_USE_BH_DEFAULT_BYTES 8192
> +#define DM_VERITY_DEFAULT_MAX_INLINE_SIZE 8192
>
> #define DM_VERITY_MAX_CORRUPTED_ERRS 100
>
> @@ -49,16 +49,16 @@ static unsigned int dm_verity_prefetch_cluster =
> DM_VERITY_DEFAULT_PREFETCH_SIZE
>
> module_param_named(prefetch_cluster, dm_verity_prefetch_cluster, uint, 0644);
>
> -static unsigned int dm_verity_use_bh_bytes[4] = {
> - DM_VERITY_USE_BH_DEFAULT_BYTES, // IOPRIO_CLASS_NONE
> - DM_VERITY_USE_BH_DEFAULT_BYTES, // IOPRIO_CLASS_RT
> - DM_VERITY_USE_BH_DEFAULT_BYTES, // IOPRIO_CLASS_BE
> +static unsigned int dm_verity_max_inline_size_bytes[4] = {
> + DM_VERITY_DEFAULT_MAX_INLINE_SIZE, // IOPRIO_CLASS_NONE
> + DM_VERITY_DEFAULT_MAX_INLINE_SIZE, // IOPRIO_CLASS_RT
> + DM_VERITY_DEFAULT_MAX_INLINE_SIZE, // IOPRIO_CLASS_BE
> 0 // IOPRIO_CLASS_IDLE
> };
>
> -module_param_array_named(use_bh_bytes, dm_verity_use_bh_bytes, uint, NULL,
> 0644);
> +module_param_array_named(use_bh_bytes, dm_verity_max_inline_size_bytes,
> uint, NULL, 0644);
>
> -static DEFINE_STATIC_KEY_FALSE(use_bh_wq_enabled);
> +static DEFINE_STATIC_KEY_FALSE(inline_verification_enabled);
>
> struct dm_verity_prefetch_work {
> struct work_struct work;
> @@ -236,13 +236,14 @@ static int verity_verify_level(struct dm_verity *v,
> struct dm_verity_io *io,
>
> verity_hash_at_level(v, block, level, &hash_block, &offset);
>
> - if (static_branch_unlikely(&use_bh_wq_enabled) && io->in_bh) {
> + if (static_branch_unlikely(&inline_verification_enabled) &&
> + !io->may_sleep) {
> data = dm_bufio_get(v->bufio, hash_block, &buf);
> if (IS_ERR_OR_NULL(data)) {
> /*
> - * In tasklet and the hash was not in the bufio cache.
> - * Return early and resume execution from a work-queue
> - * to read the hash from disk.
> + * In atomic context and the hash was not in the bufio
> + * cache. Return early and resume execution from a
> + * work-queue to read the hash from disk.
> */
> return -EAGAIN;
> }
> @@ -286,10 +287,12 @@ static int verity_verify_level(struct dm_verity *v,
> struct dm_verity_io *io,
> if (likely(memcmp(verity_io_real_digest(v, io), want_digest,
> v->digest_size) == 0))
> aux->hash_verified = 1;
> - else if (static_branch_unlikely(&use_bh_wq_enabled) &&
> io->in_bh) {
> + else if (static_branch_unlikely(&inline_verification_enabled) &&
> + !io->may_sleep) {
> /*
> - * Error handling code (FEC included) cannot be run in a
> - * tasklet since it may sleep, so fallback to
> work-queue.
> + * Error handling code (FEC included) cannot be run in
> + * atomic context since it may sleep,
> + * so fallback to work-queue.
> */
> r = -EAGAIN;
> goto release_ret_r;
> @@ -405,10 +408,11 @@ static int verity_handle_data_hash_mismatch(struct
> dm_verity *v,
> struct bio *bio, sector_t blkno,
> u8 *data)
> {
> - if (static_branch_unlikely(&use_bh_wq_enabled) && io->in_bh) {
> + if (static_branch_unlikely(&inline_verification_enabled) &&
> + !io->may_sleep) {
> /*
> - * Error handling code (FEC included) cannot be run in the
> - * BH workqueue, so fallback to a standard workqueue.
> + * Error handling code (FEC included) cannot be run in atomic
> + * context so fallback to a standard workqueue.
> */
> return -EAGAIN;
> }
> @@ -445,7 +449,8 @@ static int verity_verify_io(struct dm_verity_io *io)
> struct bio *bio = dm_bio_from_per_bio_data(io, v->ti->per_io_data_size);
> unsigned int b;
>
> - if (static_branch_unlikely(&use_bh_wq_enabled) && io->in_bh) {
> + if (static_branch_unlikely(&inline_verification_enabled) &&
> + !io->may_sleep) {
> /*
> * Copy the iterator in case we need to restart
> * verification in a work-queue.
> @@ -546,7 +551,8 @@ static void verity_finish_io(struct dm_verity_io *io,
> blk_status_t status)
> bio->bi_end_io = io->orig_bi_end_io;
> bio->bi_status = status;
>
> - if (!static_branch_unlikely(&use_bh_wq_enabled) || !io->in_bh)
> + if (!static_branch_unlikely(&inline_verification_enabled) ||
> + io->may_sleep)
> verity_fec_finish_io(io);
>
> if (unlikely(status != BLK_STS_OK) &&
> @@ -574,17 +580,22 @@ static void verity_work(struct work_struct *w)
> {
> struct dm_verity_io *io = container_of(w, struct dm_verity_io, work);
>
> - io->in_bh = false;
> + io->may_sleep = true;
>
> verity_finish_io(io, errno_to_blk_status(verity_verify_io(io)));
> }
>
> -static void verity_bh_work(struct work_struct *w)
> +static void verity_verify_inline(struct work_struct *w)
> {
> - struct dm_verity_io *io = container_of(w, struct dm_verity_io, bh_work);
> + struct dm_verity_io *io = container_of(w, struct dm_verity_io,
> inline_work);
> int err;
>
> - io->in_bh = true;
> + /*
> + * Set may_sleep to false here regardless of the context for simplicity.
> + * This ensures that we do not try to read missing hashes in contexts
> + * where we should not block.
> + */
> + io->may_sleep = false;
> err = verity_verify_io(io);
> if (err == -EAGAIN || err == -ENOMEM) {
> /* fallback to retrying with work-queue */
> @@ -596,10 +607,10 @@ static void verity_bh_work(struct work_struct *w)
> verity_finish_io(io, errno_to_blk_status(err));
> }
>
> -static inline bool verity_use_bh(unsigned int bytes, unsigned short ioprio)
> +static inline bool verity_should_verify_inline(unsigned int bytes, unsigned
> short ioprio)
> {
> return ioprio <= IOPRIO_CLASS_IDLE &&
> - bytes <= READ_ONCE(dm_verity_use_bh_bytes[ioprio]) &&
> + bytes <= READ_ONCE(dm_verity_max_inline_size_bytes[ioprio]) &&
> !need_resched();
> }
>
> @@ -617,13 +628,13 @@ static void verity_end_io(struct bio *bio)
> return;
> }
>
> - if (static_branch_unlikely(&use_bh_wq_enabled) && io->v->use_bh_wq &&
> - verity_use_bh(bytes, ioprio)) {
> + if (static_branch_unlikely(&inline_verification_enabled) &&
> io->v->verify_inline &&
> + verity_should_verify_inline(bytes, ioprio)) {
> if (in_hardirq() || irqs_disabled()) {
> - INIT_WORK(&io->bh_work, verity_bh_work);
> - queue_work(system_bh_wq, &io->bh_work);
> + INIT_WORK(&io->inline_work, verity_verify_inline);
> + queue_work(system_bh_wq, &io->inline_work);
> } else {
> - verity_bh_work(&io->bh_work);
> + verity_verify_inline(&io->inline_work);
> }
> } else {
> INIT_WORK(&io->work, verity_work);
> @@ -805,7 +816,7 @@ static void verity_status(struct dm_target *ti,
> status_type_t type,
> args++;
> if (v->validated_blocks)
> args++;
> - if (v->use_bh_wq)
> + if (v->verify_inline)
> args++;
> if (v->signature_key_desc)
> args += DM_VERITY_ROOT_HASH_VERIFICATION_OPTS;
> @@ -845,7 +856,7 @@ static void verity_status(struct dm_target *ti,
> status_type_t type,
> DMEMIT(" " DM_VERITY_OPT_IGN_ZEROES);
> if (v->validated_blocks)
> DMEMIT(" " DM_VERITY_OPT_AT_MOST_ONCE);
> - if (v->use_bh_wq)
> + if (v->verify_inline)
> DMEMIT(" " DM_VERITY_OPT_TASKLET_VERIFY);
> sz = verity_fec_status_table(v, sz, result, maxlen);
> if (v->signature_key_desc)
> @@ -1023,8 +1034,8 @@ static void verity_dtr(struct dm_target *ti)
>
> kfree(v->signature_key_desc);
>
> - if (v->use_bh_wq)
> - static_branch_dec(&use_bh_wq_enabled);
> + if (v->verify_inline)
> + static_branch_dec(&inline_verification_enabled);
>
> kfree(v);
>
> @@ -1194,8 +1205,8 @@ static int verity_parse_opt_args(struct dm_arg_set *as,
> struct dm_verity *v,
> continue;
>
> } else if (!strcasecmp(arg_name, DM_VERITY_OPT_TASKLET_VERIFY))
> {
> - v->use_bh_wq = true;
> - static_branch_inc(&use_bh_wq_enabled);
> + v->verify_inline = true;
> + static_branch_inc(&inline_verification_enabled);
> continue;
>
> } else if (verity_is_fec_opt_arg(arg_name)) {
> @@ -1526,7 +1537,7 @@ static int verity_ctr(struct dm_target *ti, unsigned
> int argc, char **argv)
> v->bufio = dm_bufio_client_create(v->hash_dev->bdev,
> 1 << v->hash_dev_block_bits, 1, sizeof(struct buffer_aux),
> dm_bufio_alloc_callback, NULL,
> - v->use_bh_wq ? DM_BUFIO_CLIENT_NO_SLEEP : 0);
> + v->verify_inline ? DM_BUFIO_CLIENT_NO_SLEEP : 0);
> if (IS_ERR(v->bufio)) {
> ti->error = "Cannot initialize dm-bufio";
> r = PTR_ERR(v->bufio);
> diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
> index 6d141abd965c..1a5233c92e54 100644
> --- a/drivers/md/dm-verity.h
> +++ b/drivers/md/dm-verity.h
> @@ -58,7 +58,7 @@ struct dm_verity {
> unsigned char levels; /* the number of tree levels */
> unsigned char version;
> bool hash_failed:1; /* set if hash of any block failed */
> - bool use_bh_wq:1; /* try to verify in BH wq before normal
> work-queue */
> + bool verify_inline:1; /* try to verify inline before normal
> work-queue */
> unsigned int digest_size; /* digest size for the current hash
> algorithm */
> enum verity_mode mode; /* mode for handling verification errors */
> enum verity_mode error_mode;/* mode for handling I/O errors */
> @@ -88,11 +88,15 @@ struct dm_verity_io {
>
> sector_t block;
> unsigned int n_blocks;
> - bool in_bh;
> + /*
> + * Keeps track of whether the request is being processed in
> + * the kworker or inline.
> + */
> + bool may_sleep;
> bool had_mismatch;
>
> struct work_struct work;
> - struct work_struct bh_work;
> + struct work_struct inline_work;
>
> u8 real_digest[HASH_MAX_DIGESTSIZE];
> u8 want_digest[HASH_MAX_DIGESTSIZE];
> --
> 2.50.0.727.gbf7dc18ff4-goog
>
