crypto: shash - remove shash_desc::flags

The flags field in 'struct shash_desc' never actually does anything.
The only ostensibly supported flag is CRYPTO_TFM_REQ_MAY_SLEEP.
However, no shash algorithm ever sleeps, making this flag a no-op.

With this being the case, inevitably some users who can't sleep wrongly
pass MAY_SLEEP.  These would all need to be fixed if any shash algorithm
actually started sleeping.  For example, the shash_ahash_*() functions,
which wrap a shash algorithm with the ahash API, pass through MAY_SLEEP
from the ahash API to the shash API.  However, the shash functions are
called under kmap_atomic(), so actually they're assumed to never sleep.

Even if it turns out that some users do need preemption points while
hashing large buffers, we could easily provide a helper function
crypto_shash_update_large() which divides the data into smaller chunks
and calls crypto_shash_update() and cond_resched() for each chunk.  It's
not necessary to have a flag in 'struct shash_desc', nor is it necessary
to make individual shash algorithms aware of this at all.

Therefore, remove shash_desc::flags, and document that the
crypto_shash_*() functions can be called from any context.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

lib/crc-t10dif.c

@@ -69,7 +69,6 @@ __u16 crc_t10dif_update(__u16 crc, const unsigned char *buffer, size_t len)
 
 	rcu_read_lock();
 	desc.shash.tfm = rcu_dereference(crct10dif_tfm);
-	desc.shash.flags = 0;
 	*(__u16 *)desc.ctx = crc;
 
 	err = crypto_shash_update(&desc.shash, buffer, len);

lib/digsig.c

@@ -240,7 +240,6 @@ int digsig_verify(struct key *keyring, const char *sig, int siglen,
 		goto err;
 
 	desc->tfm = shash;
-	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 
 	crypto_shash_init(desc);
 	crypto_shash_update(desc, data, datalen);

lib/libcrc32c.c

@@ -47,7 +47,6 @@ u32 crc32c(u32 crc, const void *address, unsigned int length)
 	int err;
 
 	shash->tfm = tfm;
-	shash->flags = 0;
 	*ctx = crc;
 
 	err = crypto_shash_update(shash, address, length);