On Tue, 11 Aug 2026, Runyu Xiao wrote:
> crypt_alloc_buffer() conditionally acquires bio_alloc_lock around the
> allocation path and also contains the retry logic for the reclaim
> fallback.
>
> Move one allocation attempt into crypt_alloc_buffer_try() so that
> bio_alloc_lock is always acquired and released in crypt_alloc_buffer(),
> and the retry decision is made only after the mutex has been dropped.
>
> This keeps the retry path outside the locked region and makes the
> locking context easier to analyze.
>
> Signed-off-by: Runyu Xiao <[email protected]>
Hi
I wouldn't do this. The patch just moves code around and increases code
size with no benefit.
Mikulas
> ---
> Changes in v2:
> - Move one allocation attempt into crypt_alloc_buffer_try(), as suggested
> by Bart Van Assche.
> - Keep bio_alloc_lock acquisition and release in crypt_alloc_buffer(), and
> make the retry decision only after releasing the lock.
> - Preserve the distinction between a page-pool retry and a final integrity
> allocation failure.
>
> v1: https://lore.kernel.org/r/[email protected]
>
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index 608b617fb817..7c68fad12960 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -1627,18 +1627,16 @@ static void crypt_free_buffer_pages(struct
> crypt_config *cc, struct bio *clone);
> * In order to reduce allocation overhead, we try to allocate compound pages
> in
> * the first pass. If they are not available, we fall back to the mempool.
> */
> -static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned int
> size)
> +static struct bio *crypt_alloc_buffer_try(struct dm_crypt_io *io,
> + unsigned int size, gfp_t gfp_mask,
> + unsigned int order, bool *retry)
> {
> struct crypt_config *cc = io->cc;
> struct bio *clone;
> unsigned int nr_iovecs = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> - gfp_t gfp_mask = GFP_NOWAIT | __GFP_HIGHMEM;
> unsigned int remaining_size;
> - unsigned int order = MAX_PAGE_ORDER;
>
> -retry:
> - if (unlikely(gfp_mask & __GFP_DIRECT_RECLAIM))
> - mutex_lock(&cc->bio_alloc_lock);
> + *retry = false;
>
> clone = bio_alloc_bioset(cc->dev->bdev, nr_iovecs, io->base_bio->bi_opf,
> GFP_NOIO, &cc->bs);
> @@ -1674,9 +1672,8 @@ static struct bio *crypt_alloc_buffer(struct
> dm_crypt_io *io, unsigned int size)
> if (!pages) {
> crypt_free_buffer_pages(cc, clone);
> bio_put(clone);
> - gfp_mask |= __GFP_DIRECT_RECLAIM;
> - order = 0;
> - goto retry;
> + *retry = true;
> + return NULL;
> }
>
> have_pages:
> @@ -1692,12 +1689,34 @@ static struct bio *crypt_alloc_buffer(struct
> dm_crypt_io *io, unsigned int size)
> clone = NULL;
> }
>
> - if (unlikely(gfp_mask & __GFP_DIRECT_RECLAIM))
> - mutex_unlock(&cc->bio_alloc_lock);
> -
> return clone;
> }
>
> +static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned int
> size)
> +{
> + struct crypt_config *cc = io->cc;
> + struct bio *clone;
> + gfp_t gfp_mask = GFP_NOWAIT | __GFP_HIGHMEM;
> + unsigned int order = MAX_PAGE_ORDER;
> + bool retry;
> +
> + for (;;) {
> + if (unlikely(gfp_mask & __GFP_DIRECT_RECLAIM))
> + mutex_lock(&cc->bio_alloc_lock);
> +
> + clone = crypt_alloc_buffer_try(io, size, gfp_mask, order,
> &retry);
> +
> + if (unlikely(gfp_mask & __GFP_DIRECT_RECLAIM))
> + mutex_unlock(&cc->bio_alloc_lock);
> +
> + if (!retry)
> + return clone;
> +
> + gfp_mask |= __GFP_DIRECT_RECLAIM;
> + order = 0;
> + }
> +}
> +
> static void crypt_free_buffer_pages(struct crypt_config *cc, struct bio
> *clone)
> {
> struct folio_iter fi;
> --
> 2.34.1
>
