crypto: xts - Fix atomic sleep when walking skcipher

When we perform a walk in the completion function, we need to ensure
that it is atomic.

Reported-by: syzbot+6f72c20560060c98b566@syzkaller.appspotmail.com
Fixes: 78105c7e ("crypto: xts - Drop use of auxiliary buffer")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/xts.c

@@ -137,8 +137,12 @@ static void crypt_done(struct crypto_async_request *areq, int err)
 {
 	struct skcipher_request *req = areq->data;
 
-	if (!err)
+	if (!err) {
+		struct rctx *rctx = skcipher_request_ctx(req);
+
+		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
 		err = xor_tweak_post(req);
+	}
 
 	skcipher_request_complete(req, err);
 }