Re: [PATCH v2] blk-crypto-fallback: Fix deadlock when encrypting large bio in dm layer

[Christoph Hellwig]

On Tue, Aug 11, 2026 at 03:03:18PM -0700, Eric Biggers wrote:
> Encrypting a large bio with more than BIO_MAX_VECS pages can still
> deadlock, even after it was attempted to be fixed by
> commit b37fbce460ad ("blk-crypto: optimize bio splitting in
> blk_crypto_fallback_encrypt_bio") and commit 3d939695e682 ("blk-crypto:
> use mempool_alloc_bulk for encrypted bio page allocation").
> 
> This is because __blk_crypto_fallback_encrypt_bio() assumes that the
> bounce bios that it submits will eventually complete, unblocking it from
> allocating additional bounce bios and pages.  However, dm-inlinecrypt.c
> calls __blk_crypto_submit_bio() from within submit_bio() itself.  In
> this case, the recursive submit_bio() simply adds the bounce bio to
> current->bio_list without actually submitting it yet.  That breaks the
> guarantee that forward progress is being made.
> 
> To fix this, allocate the bio and bounce pages with GFP_NOWAIT if
> current->bio_list is set.  If it fails, punt the encryption of the
> remaining part of the bio to a kworker.
> 
> Fixes: 488f6682c832 ("block: blk-crypto-fallback for Inline Encryption")

No, it dos not fix that commit.  I "fixes" the misguided attempt to use
this from inside stackable drivers.  Let's drop the dm-inlinecrypt
target instead as this just shows up one more reason why that is a
broken idea.

> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
> 
> Changed in v2:
> - Switched to the less efficient approach preferred by Christoph

This is in no way the approach I prefer or even advocated for.