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  1. Jul 07, 2022
    • Steven Lung's avatar
      dm cache: fix typo in 2 comment blocks · 5c29e784
      Steven Lung authored 
      

Replace neccessarily with necessarily.

Signed-off-by: default avatarSteven Lung <1030steven@gmail.com>
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
      5c29e784
    • JeongHyeon Lee's avatar
      dm verity: fix checkpatch close brace error · 20e6fc85
      JeongHyeon Lee authored 
      

Resolves: ERROR: else should follow close brace '}'

Signed-off-by: default avatarJeongHyeon Lee <jhs2.lee@samsung.com>
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
      20e6fc85
    • Mike Snitzer's avatar
      dm table: rename dm_target variable in dm_table_add_target() · 899ab445
      Mike Snitzer authored 
      

Rename from "tgt" to "ti" so that all of dm-table.c code uses the same
naming for dm_target variables.

Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
      899ab445
    • Mike Snitzer's avatar
      dm table: audit all dm_table_get_target() callers · 564b5c54
      Mike Snitzer authored 
      

All callers of dm_table_get_target() are expected to do proper bounds
checking on the index they pass.

Move dm_table_get_target() to dm-core.h to make it extra clear that only
DM core code should be using it. Switch it to be inlined while at it.

Standardize all DM core callers to use the same for loop pattern and
make associated variables as local as possible. Rename some variables
(e.g. s/table/t/ and s/tgt/ti/) along the way.

Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
      564b5c54
    • Mike Snitzer's avatar
      dm table: remove dm_table_get_num_targets() wrapper · 2aec377a
      Mike Snitzer authored 
      

More efficient and readable to just access table->num_targets directly.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
      2aec377a
    • Ming Lei's avatar
      dm: add two stage requeue mechanism · 8b211aac
      Ming Lei authored 
      Commit 61b6e2e5 ("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
7dd76d1f ("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
61b6e2e5

.

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: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
      8b211aac
    • Ming Lei's avatar
      dm: add dm_bio_rewind() API to DM core · 61cbe788
      Ming Lei authored 
      Commit 7759eb23 ("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 5151842b (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 7dd76d1f

 ("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: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
      61cbe788
  3. Jun 30, 2022
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