linux/drivers/md/dm-io-rewind.c

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// SPDX-License-Identifier: GPL-2.0-only
dm: add dm_bio_rewind() API to DM core Commit 7759eb23fd98 ("block: remove bio_rewind_iter()") removed a similar API for the following reasons: ``` It is pointed that bio_rewind_iter() is one very bad API[1]: 1) bio size may not be restored after rewinding 2) it causes some bogus change, such as 5151842b9d8732 (block: reset bi_iter.bi_done after splitting bio) 3) rewinding really makes things complicated wrt. bio splitting 4) unnecessary updating of .bi_done in fast path [1] https://marc.info/?t=153549924200005&r=1&w=2 So this patch takes Kent's suggestion to restore one bio into its original state via saving bio iterator(struct bvec_iter) in bio_integrity_prep(), given now bio_rewind_iter() is only used by bio integrity code. ``` However, saving off a copy of the 32 bytes bio->bi_iter in case rewind needed isn't efficient because it bloats per-bio-data for what is an unlikely case. That suggestion also ignores the need to restore crypto and integrity info. Add dm_bio_rewind() API for a specific use-case that is much more narrow than the previous more generic rewind code that was reverted: 1) most bios have a fixed end sector since bio split is done from front of the bio, if driver just records how many sectors between current bio's start sector and the original bio's end sector, the original position can be restored. Keeping the original bio's end sector fixed is a _hard_ requirement for this interface! 2) if a bio's end sector won't change (usually bio_trim() isn't called, or in the case of DM it preserves original bio), user can restore the original position by storing sector offset from the current ->bi_iter.bi_sector to bio's end sector; together with saving bio size, only 8 bytes is needed to restore to original bio. 3) DM's requeue use case: when BLK_STS_DM_REQUEUE happens, DM core needs to restore to an "original bio" which represents the current dm_io to be requeued (which may be a subset of the original bio). By storing the sector offset from the original bio's end sector and dm_io's size, dm_bio_rewind() can restore such original bio. See commit 7dd76d1feec7 ("dm: improve bio splitting and associated IO accounting") for more details on how DM does this. Leveraging this, allows DM core to shift the need for bio cloning from bio-split time (during IO submission) to the less likely BLK_STS_DM_REQUEUE handling (after IO completes with that error). 4) Unlike the original rewind API, dm_bio_rewind() doesn't add .bi_done to bvec_iter and there is no effect on the fast path. Implement dm_bio_rewind() by factoring out clear helpers that it calls: dm_bio_integrity_rewind, dm_bio_crypt_rewind and dm_bio_rewind_iter. DM is able to ensure that dm_bio_rewind() is used safely but, given the constraint that the bio's end must never change, other hypothetical future callers may not take the same care. So make dm_bio_rewind() and all supporting code local to DM to avoid risk of hypothetical abuse. A "dm_" prefix was added to all functions to avoid any namespace collisions. Suggested-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
2022-06-24 22:12:52 +08:00
/*
* Copyright 2022 Red Hat, Inc.
*/
#include <linux/bio.h>
#include <linux/blk-crypto.h>
#include <linux/blk-integrity.h>
#include "dm-core.h"
static inline bool dm_bvec_iter_rewind(const struct bio_vec *bv,
struct bvec_iter *iter,
unsigned int bytes)
{
int idx;
iter->bi_size += bytes;
if (bytes <= iter->bi_bvec_done) {
iter->bi_bvec_done -= bytes;
return true;
}
bytes -= iter->bi_bvec_done;
idx = iter->bi_idx - 1;
while (idx >= 0 && bytes && bytes > bv[idx].bv_len) {
bytes -= bv[idx].bv_len;
idx--;
}
if (WARN_ONCE(idx < 0 && bytes,
"Attempted to rewind iter beyond bvec's boundaries\n")) {
iter->bi_size -= bytes;
iter->bi_bvec_done = 0;
iter->bi_idx = 0;
return false;
}
iter->bi_idx = idx;
iter->bi_bvec_done = bv[idx].bv_len - bytes;
return true;
}
#if defined(CONFIG_BLK_DEV_INTEGRITY)
/**
* dm_bio_integrity_rewind - Rewind integrity vector
* @bio: bio whose integrity vector to update
* @bytes_done: number of data bytes to rewind
*
* Description: This function calculates how many integrity bytes the
* number of completed data bytes correspond to and rewind the
* integrity vector accordingly.
*/
static void dm_bio_integrity_rewind(struct bio *bio, unsigned int bytes_done)
{
struct bio_integrity_payload *bip = bio_integrity(bio);
struct blk_integrity *bi = blk_get_integrity(bio->bi_bdev->bd_disk);
unsigned int bytes = bio_integrity_bytes(bi, bytes_done >> 9);
dm: add dm_bio_rewind() API to DM core Commit 7759eb23fd98 ("block: remove bio_rewind_iter()") removed a similar API for the following reasons: ``` It is pointed that bio_rewind_iter() is one very bad API[1]: 1) bio size may not be restored after rewinding 2) it causes some bogus change, such as 5151842b9d8732 (block: reset bi_iter.bi_done after splitting bio) 3) rewinding really makes things complicated wrt. bio splitting 4) unnecessary updating of .bi_done in fast path [1] https://marc.info/?t=153549924200005&r=1&w=2 So this patch takes Kent's suggestion to restore one bio into its original state via saving bio iterator(struct bvec_iter) in bio_integrity_prep(), given now bio_rewind_iter() is only used by bio integrity code. ``` However, saving off a copy of the 32 bytes bio->bi_iter in case rewind needed isn't efficient because it bloats per-bio-data for what is an unlikely case. That suggestion also ignores the need to restore crypto and integrity info. Add dm_bio_rewind() API for a specific use-case that is much more narrow than the previous more generic rewind code that was reverted: 1) most bios have a fixed end sector since bio split is done from front of the bio, if driver just records how many sectors between current bio's start sector and the original bio's end sector, the original position can be restored. Keeping the original bio's end sector fixed is a _hard_ requirement for this interface! 2) if a bio's end sector won't change (usually bio_trim() isn't called, or in the case of DM it preserves original bio), user can restore the original position by storing sector offset from the current ->bi_iter.bi_sector to bio's end sector; together with saving bio size, only 8 bytes is needed to restore to original bio. 3) DM's requeue use case: when BLK_STS_DM_REQUEUE happens, DM core needs to restore to an "original bio" which represents the current dm_io to be requeued (which may be a subset of the original bio). By storing the sector offset from the original bio's end sector and dm_io's size, dm_bio_rewind() can restore such original bio. See commit 7dd76d1feec7 ("dm: improve bio splitting and associated IO accounting") for more details on how DM does this. Leveraging this, allows DM core to shift the need for bio cloning from bio-split time (during IO submission) to the less likely BLK_STS_DM_REQUEUE handling (after IO completes with that error). 4) Unlike the original rewind API, dm_bio_rewind() doesn't add .bi_done to bvec_iter and there is no effect on the fast path. Implement dm_bio_rewind() by factoring out clear helpers that it calls: dm_bio_integrity_rewind, dm_bio_crypt_rewind and dm_bio_rewind_iter. DM is able to ensure that dm_bio_rewind() is used safely but, given the constraint that the bio's end must never change, other hypothetical future callers may not take the same care. So make dm_bio_rewind() and all supporting code local to DM to avoid risk of hypothetical abuse. A "dm_" prefix was added to all functions to avoid any namespace collisions. Suggested-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
2022-06-24 22:12:52 +08:00
bip->bip_iter.bi_sector -= bio_integrity_intervals(bi, bytes_done >> 9);
dm_bvec_iter_rewind(bip->bip_vec, &bip->bip_iter, bytes);
}
#else /* CONFIG_BLK_DEV_INTEGRITY */
static inline void dm_bio_integrity_rewind(struct bio *bio,
unsigned int bytes_done)
{
}
#endif
#if defined(CONFIG_BLK_INLINE_ENCRYPTION)
/* Decrements @dun by @dec, treating @dun as a multi-limb integer. */
static void dm_bio_crypt_dun_decrement(u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE],
unsigned int dec)
{
int i;
for (i = 0; dec && i < BLK_CRYPTO_DUN_ARRAY_SIZE; i++) {
u64 prev = dun[i];
dun[i] -= dec;
if (dun[i] > prev)
dec = 1;
else
dec = 0;
}
}
static void dm_bio_crypt_rewind(struct bio *bio, unsigned int bytes)
{
struct bio_crypt_ctx *bc = bio->bi_crypt_context;
dm_bio_crypt_dun_decrement(bc->bc_dun,
bytes >> bc->bc_key->data_unit_size_bits);
}
#else /* CONFIG_BLK_INLINE_ENCRYPTION */
static inline void dm_bio_crypt_rewind(struct bio *bio, unsigned int bytes)
{
}
#endif
static inline void dm_bio_rewind_iter(const struct bio *bio,
struct bvec_iter *iter, unsigned int bytes)
{
iter->bi_sector -= bytes >> 9;
/* No advance means no rewind */
if (bio_no_advance_iter(bio))
iter->bi_size += bytes;
else
dm_bvec_iter_rewind(bio->bi_io_vec, iter, bytes);
}
/**
* dm_bio_rewind - update ->bi_iter of @bio by rewinding @bytes.
* @bio: bio to rewind
* @bytes: how many bytes to rewind
*
* WARNING:
* Caller must ensure that @bio has a fixed end sector, to allow
* rewinding from end of bio and restoring its original position.
* Caller is also responsibile for restoring bio's size.
*/
static void dm_bio_rewind(struct bio *bio, unsigned int bytes)
dm: add dm_bio_rewind() API to DM core Commit 7759eb23fd98 ("block: remove bio_rewind_iter()") removed a similar API for the following reasons: ``` It is pointed that bio_rewind_iter() is one very bad API[1]: 1) bio size may not be restored after rewinding 2) it causes some bogus change, such as 5151842b9d8732 (block: reset bi_iter.bi_done after splitting bio) 3) rewinding really makes things complicated wrt. bio splitting 4) unnecessary updating of .bi_done in fast path [1] https://marc.info/?t=153549924200005&r=1&w=2 So this patch takes Kent's suggestion to restore one bio into its original state via saving bio iterator(struct bvec_iter) in bio_integrity_prep(), given now bio_rewind_iter() is only used by bio integrity code. ``` However, saving off a copy of the 32 bytes bio->bi_iter in case rewind needed isn't efficient because it bloats per-bio-data for what is an unlikely case. That suggestion also ignores the need to restore crypto and integrity info. Add dm_bio_rewind() API for a specific use-case that is much more narrow than the previous more generic rewind code that was reverted: 1) most bios have a fixed end sector since bio split is done from front of the bio, if driver just records how many sectors between current bio's start sector and the original bio's end sector, the original position can be restored. Keeping the original bio's end sector fixed is a _hard_ requirement for this interface! 2) if a bio's end sector won't change (usually bio_trim() isn't called, or in the case of DM it preserves original bio), user can restore the original position by storing sector offset from the current ->bi_iter.bi_sector to bio's end sector; together with saving bio size, only 8 bytes is needed to restore to original bio. 3) DM's requeue use case: when BLK_STS_DM_REQUEUE happens, DM core needs to restore to an "original bio" which represents the current dm_io to be requeued (which may be a subset of the original bio). By storing the sector offset from the original bio's end sector and dm_io's size, dm_bio_rewind() can restore such original bio. See commit 7dd76d1feec7 ("dm: improve bio splitting and associated IO accounting") for more details on how DM does this. Leveraging this, allows DM core to shift the need for bio cloning from bio-split time (during IO submission) to the less likely BLK_STS_DM_REQUEUE handling (after IO completes with that error). 4) Unlike the original rewind API, dm_bio_rewind() doesn't add .bi_done to bvec_iter and there is no effect on the fast path. Implement dm_bio_rewind() by factoring out clear helpers that it calls: dm_bio_integrity_rewind, dm_bio_crypt_rewind and dm_bio_rewind_iter. DM is able to ensure that dm_bio_rewind() is used safely but, given the constraint that the bio's end must never change, other hypothetical future callers may not take the same care. So make dm_bio_rewind() and all supporting code local to DM to avoid risk of hypothetical abuse. A "dm_" prefix was added to all functions to avoid any namespace collisions. Suggested-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
2022-06-24 22:12:52 +08:00
{
if (bio_integrity(bio))
dm_bio_integrity_rewind(bio, bytes);
if (bio_has_crypt_ctx(bio))
dm_bio_crypt_rewind(bio, bytes);
dm_bio_rewind_iter(bio, &bio->bi_iter, bytes);
}
dm: add two stage requeue mechanism Commit 61b6e2e5321d ("dm: fix BLK_STS_DM_REQUEUE handling when dm_io represents split bio") reverted DM core's bio splitting back to using bio_split()+bio_chain() because it was found that otherwise DM's BLK_STS_DM_REQUEUE would trigger a live-lock waiting for bio completion that would never occur. Restore using bio_trim()+bio_inc_remaining(), like was done in commit 7dd76d1feec7 ("dm: improve bio splitting and associated IO accounting"), but this time with proper handling for the above scenario that is covered in more detail in the commit header for 61b6e2e5321d. Solve this issue by adding a two staged dm_io requeue mechanism that uses the new dm_bio_rewind() via dm_io_rewind(): 1) requeue the dm_io into the requeue_list added to struct mapped_device, and schedule it via new added requeue work. This workqueue just clones the dm_io->orig_bio (which DM saves and ensures its end sector isn't modified). dm_io_rewind() uses the sectors and sectors_offset members of the dm_io that are recorded relative to the end of orig_bio: dm_bio_rewind()+bio_trim() are then used to make that cloned bio reflect the subset of the original bio that is represented by the dm_io that is being requeued. 2) the 2nd stage requeue is same with original requeue, but io->orig_bio points to new cloned bio (which matches the requeued dm_io as described above). This allows DM core to shift the need for bio cloning from bio-split time (during IO submission) to the less likely BLK_STS_DM_REQUEUE handling (after IO completes with that error). Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
2022-06-24 22:12:55 +08:00
void dm_io_rewind(struct dm_io *io, struct bio_set *bs)
{
struct bio *orig = io->orig_bio;
struct bio *new_orig = bio_alloc_clone(orig->bi_bdev, orig,
GFP_NOIO, bs);
/*
* dm_bio_rewind can restore to previous position since the
* end sector is fixed for original bio, but we still need
* to restore bio's size manually (using io->sectors).
*/
dm_bio_rewind(new_orig, ((io->sector_offset << 9) -
orig->bi_iter.bi_size));
bio_trim(new_orig, 0, io->sectors);
bio_chain(new_orig, orig);
/*
* __bi_remaining was increased (by dm_split_and_process_bio),
* so must drop the one added in bio_chain.
*/
atomic_dec(&orig->__bi_remaining);
io->orig_bio = new_orig;
}