Hi If you allocate memory in crypto processing in dm-integrity, you risk the low-memory deadlock when swapping to dm-integrity. I.e. the machine runs out of memory, it needs to swap out pages to free some memory, the swap-out bio goes to dm-integrity and dm-integrity calls the crypto API and tries to allocate more memory => deadlock. On Wed, 5 Jul 2023, Eric Biggers wrote: > On Wed, Jul 05, 2023 at 05:40:07PM +0100, Giovanni Cabiddu wrote: > > The flag CRYPTO_ALG_ALLOCATES_MEMORY indicates that an algorithm might > > allocate memory in the datapath and therefore sleep. > > Dm-integrity is filtering out implementations of skcipher algorithms > > that have this flag set. However, in the same function it does > > allocations with GFP_KERNEL. It's OK to use GFP_KERNEL in the device mapper target constructor (because at this point there is no I/O going to the device). But it's not OK to use it for individual bio processing. > Which function is the above referring to? The actual encryption/decryption > happens in crypt_journal(), and I don't see any memory allocations there. > > > As dm-integrity is re-entrant and capable of handling sleeps that could > > occur during allocations with GFP_KERNEL, then it is also capable of > > using skcipher algorithm implementations that have > > CRYPTO_ALG_ALLOCATES_MEMORY set. > > > > Remove the filtering of skcipher implementations with the flag > > CRYPTO_ALG_ALLOCATES_MEMORY set. > > What about the use of CRYPTO_ALG_ALLOCATES_MEMORY in get_mac()? > > > > > Suggested-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> > > Link: https://lore.kernel.org/linux-crypto/ZILvtASXQKLG43y9@xxxxxxxxxxxxxxxxxxx/ > > Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@xxxxxxxxx> > > Reviewed-by: Fiona Trahe <fiona.trahe@xxxxxxxxx> > > This needs: > > Fixes: a7a10bce8a04 ("dm integrity: don't use drivers that have CRYPTO_ALG_ALLOCATES_MEMORY") > Cc: stable@xxxxxxxxxxxxxxx > > But, are you 100% sure the explanation in commit a7a10bce8a04 was incorrect? > > - Eric Mikulas
