On Tue, 7 Jan 2020, Joe Thornber wrote:
> On Tue, Jan 07, 2020 at 10:46:27AM +0000, Joe Thornber wrote:
> > I'll get a patch to you later today.
>
> Eric,
>
> Patch below. I've run it through a bunch of tests in the dm test suite. But
> obviously I have never hit your issue. Will do more testing today.
Thank you Joe, I'll apply the patch and pull out the spinlock.
I'm not familiar with how sync IO prevents a spinlock. Can you give a
brief explaination or point me at documentation?
--
Eric Wheeler
>
> - Joe
>
>
>
> Author: Joe Thornber <ejt@xxxxxxxxxx>
> Date: Tue Jan 7 11:58:42 2020 +0000
>
> [dm-thin, dm-cache] Fix bug in space-maps.
>
> The space-maps track the reference counts for disk blocks. There are variants
> for tracking metadata blocks, and data blocks.
>
> We implement transactionality by never touching blocks from the previous
> transaction, so we can rollback in the event of a crash.
>
> When allocating a new block we need to ensure the block is free (has reference
> count of 0) in both the current and previous transaction. Prior to this patch we
> were doing this by searching for a free block in the previous transaction, and
> relying on a 'begin' counter to track where the last allocation in the current
> transaction was. This 'begin' field was not being updated in all code paths (eg,
> increment of a data block reference count due to breaking sharing of a neighbour
> block in the same btree leaf).
>
> This patch keeps the 'begin' field, but now it's just a hint to speed up the search.
> Instead we search the current transaction for a free block, and then double check
> it's free in the old transaction. Much simpler.
>
> diff --git a/drivers/md/persistent-data/dm-space-map-common.c b/drivers/md/persistent-data/dm-space-map-common.c
> index bd68f6fef694..b4983e4022e6 100644
> --- a/drivers/md/persistent-data/dm-space-map-common.c
> +++ b/drivers/md/persistent-data/dm-space-map-common.c
> @@ -380,6 +380,34 @@ int sm_ll_find_free_block(struct ll_disk *ll, dm_block_t begin,
> return -ENOSPC;
> }
>
> +int sm_ll_find_common_free_block(struct ll_disk *old_ll, struct ll_disk *new_ll,
> + dm_block_t begin, dm_block_t end, dm_block_t *b)
> +{
> + int r;
> + uint32_t count;
> +
> + do {
> + r = sm_ll_find_free_block(new_ll, begin, new_ll->nr_blocks, b);
> + if (r)
> + break;
> +
> + /* double check this block wasn't used in the old transaction */
> + if (*b >= old_ll->nr_blocks)
> + count = 0;
> +
> + else {
> + r = sm_ll_lookup(old_ll, *b, &count);
> + if (r)
> + break;
> +
> + if (count)
> + begin = *b + 1;
> + }
> + } while (count);
> +
> + return r;
> +}
> +
> static int sm_ll_mutate(struct ll_disk *ll, dm_block_t b,
> int (*mutator)(void *context, uint32_t old, uint32_t *new),
> void *context, enum allocation_event *ev)
> diff --git a/drivers/md/persistent-data/dm-space-map-common.h b/drivers/md/persistent-data/dm-space-map-common.h
> index b3078d5eda0c..8de63ce39bdd 100644
> --- a/drivers/md/persistent-data/dm-space-map-common.h
> +++ b/drivers/md/persistent-data/dm-space-map-common.h
> @@ -109,6 +109,8 @@ int sm_ll_lookup_bitmap(struct ll_disk *ll, dm_block_t b, uint32_t *result);
> int sm_ll_lookup(struct ll_disk *ll, dm_block_t b, uint32_t *result);
> int sm_ll_find_free_block(struct ll_disk *ll, dm_block_t begin,
> dm_block_t end, dm_block_t *result);
> +int sm_ll_find_common_free_block(struct ll_disk *old_ll, struct ll_disk *new_ll,
> + dm_block_t begin, dm_block_t end, dm_block_t *result);
> int sm_ll_insert(struct ll_disk *ll, dm_block_t b, uint32_t ref_count, enum allocation_event *ev);
> int sm_ll_inc(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev);
> int sm_ll_dec(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev);
> diff --git a/drivers/md/persistent-data/dm-space-map-disk.c b/drivers/md/persistent-data/dm-space-map-disk.c
> index 32adf6b4a9c7..bf4c5e2ccb6f 100644
> --- a/drivers/md/persistent-data/dm-space-map-disk.c
> +++ b/drivers/md/persistent-data/dm-space-map-disk.c
> @@ -167,8 +167,10 @@ static int sm_disk_new_block(struct dm_space_map *sm, dm_block_t *b)
> enum allocation_event ev;
> struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
>
> - /* FIXME: we should loop round a couple of times */
> - r = sm_ll_find_free_block(&smd->old_ll, smd->begin, smd->old_ll.nr_blocks, b);
> + /*
> + * Any block we allocate has to be free in both the old and current ll.
> + */
> + r = sm_ll_find_common_free_block(&smd->old_ll, &smd->ll, smd->begin, smd->ll.nr_blocks, b);
> if (r)
> return r;
>
> diff --git a/drivers/md/persistent-data/dm-space-map-metadata.c b/drivers/md/persistent-data/dm-space-map-metadata.c
> index 25328582cc48..9e3c64ec2026 100644
> --- a/drivers/md/persistent-data/dm-space-map-metadata.c
> +++ b/drivers/md/persistent-data/dm-space-map-metadata.c
> @@ -448,7 +448,10 @@ static int sm_metadata_new_block_(struct dm_space_map *sm, dm_block_t *b)
> enum allocation_event ev;
> struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
>
> - r = sm_ll_find_free_block(&smm->old_ll, smm->begin, smm->old_ll.nr_blocks, b);
> + /*
> + * Any block we allocate has to be free in both the old and current ll.
> + */
> + r = sm_ll_find_common_free_block(&smm->old_ll, &smm->ll, smm->begin, smm->ll.nr_blocks, b);
> if (r)
> return r;
>
>
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>
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