Re: Deadlock when using crypto API for block devices
From: Mikulas Patocka
Date: Fri Aug 24 2018 - 07:22:25 EST
On Fri, 24 Aug 2018, Mikulas Patocka wrote:
> On Fri, 24 Aug 2018, Herbert Xu wrote:
> > On Thu, Aug 23, 2018 at 04:39:23PM -0400, Mikulas Patocka wrote:
> > >
> > > 1. don't set CRYPTO_TFM_REQ_MAY_SLEEP in dm-crypt
> > > =================================================
> > > If we don't set it, dm-crypt will use GFP_ATOMIC and GFP_ATOMIC may fail.
> > > The function init_crypt in xts.c handles the failure gracefully - but the
> > > question is - does the whole crypto code handle allocation failures
> > > gracefully? If not and if it returns -ENOMEM somewhere, it would result in
> > > I/O errors and data corruption.
> > It is safe to use GFP_ATOMIC. First of the allocation is really
> > small (less than a page) so it will only fail when the system is
> > almost completely out of memory.
> GFP_ATOMIC is used by networking code. If the system is in a situation
> when packets arrive faster than the swapper is able to swap, it will
> happen. It does happen during netwoking surge and corrupting the
> filesystem in tris situation is not acceptable.
> > Even when it does fail the crypto
> > operation will still succeed, albeit it will process things at a
> > smaller granularity so the performance will degrade.
> A quick search through the crypto code shows that ahash_save_req and
> seqiv_aead_encrypt return -ENOMEM.
> Will you fix them?
And also ablkcipher_next_slow, ablkcipher_copy_iv, skcipher_next_slow,
skcipher_next_copy, skcipher_copy_iv, blkcipher_next_slow,
So, I think that dropping CRYPTO_TFM_REQ_MAY_SLEEP is not possible.