Revision 4f988f152ee087831ea5c1c77cda4454cacc052c authored by Linus Torvalds on 04 May 2012, 22:13:54 UTC, committed by Linus Torvalds on 04 May 2012, 22:13:54 UTC
The normal read_seqcount_begin() function will wait for any current writers to exit their critical region by looping until the sequence count is even. That "wait for sequence count to stabilize" is the right thing to do if the read-locker will just retry the whole operation on contention: no point in doing a potentially expensive reader sequence if we know at the beginning that we'll just end up re-doing it all. HOWEVER. Some users don't actually retry the operation, but instead will abort and do the operation with proper locking. So the sequence count case may be the optimistic quick case, but in the presense of writers you may want to do full locking in order to guarantee forward progress. The prime example of this would be the RCU name lookup. And in that case, you may well be better off without the "retry early", and are in a rush to instead get to the failure handling. Thus this "raw" interface that just returns the sequence number without testing it - it just forces the low bit to zero so that read_seqcount_retry() will always fail such a "active concurrent writer" scenario. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 2f62427
chainiv.c
/*
* chainiv: Chain IV Generator
*
* Generate IVs simply be using the last block of the previous encryption.
* This is mainly useful for CBC with a synchronous algorithm.
*
* Copyright (c) 2007 Herbert Xu <herbert@gondor.apana.org.au>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option)
* any later version.
*
*/
#include <crypto/internal/skcipher.h>
#include <crypto/rng.h>
#include <crypto/crypto_wq.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/workqueue.h>
enum {
CHAINIV_STATE_INUSE = 0,
};
struct chainiv_ctx {
spinlock_t lock;
char iv[];
};
struct async_chainiv_ctx {
unsigned long state;
spinlock_t lock;
int err;
struct crypto_queue queue;
struct work_struct postponed;
char iv[];
};
static int chainiv_givencrypt(struct skcipher_givcrypt_request *req)
{
struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
struct chainiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
struct ablkcipher_request *subreq = skcipher_givcrypt_reqctx(req);
unsigned int ivsize;
int err;
ablkcipher_request_set_tfm(subreq, skcipher_geniv_cipher(geniv));
ablkcipher_request_set_callback(subreq, req->creq.base.flags &
~CRYPTO_TFM_REQ_MAY_SLEEP,
req->creq.base.complete,
req->creq.base.data);
ablkcipher_request_set_crypt(subreq, req->creq.src, req->creq.dst,
req->creq.nbytes, req->creq.info);
spin_lock_bh(&ctx->lock);
ivsize = crypto_ablkcipher_ivsize(geniv);
memcpy(req->giv, ctx->iv, ivsize);
memcpy(subreq->info, ctx->iv, ivsize);
err = crypto_ablkcipher_encrypt(subreq);
if (err)
goto unlock;
memcpy(ctx->iv, subreq->info, ivsize);
unlock:
spin_unlock_bh(&ctx->lock);
return err;
}
static int chainiv_givencrypt_first(struct skcipher_givcrypt_request *req)
{
struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
struct chainiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
int err = 0;
spin_lock_bh(&ctx->lock);
if (crypto_ablkcipher_crt(geniv)->givencrypt !=
chainiv_givencrypt_first)
goto unlock;
crypto_ablkcipher_crt(geniv)->givencrypt = chainiv_givencrypt;
err = crypto_rng_get_bytes(crypto_default_rng, ctx->iv,
crypto_ablkcipher_ivsize(geniv));
unlock:
spin_unlock_bh(&ctx->lock);
if (err)
return err;
return chainiv_givencrypt(req);
}
static int chainiv_init_common(struct crypto_tfm *tfm)
{
tfm->crt_ablkcipher.reqsize = sizeof(struct ablkcipher_request);
return skcipher_geniv_init(tfm);
}
static int chainiv_init(struct crypto_tfm *tfm)
{
struct chainiv_ctx *ctx = crypto_tfm_ctx(tfm);
spin_lock_init(&ctx->lock);
return chainiv_init_common(tfm);
}
static int async_chainiv_schedule_work(struct async_chainiv_ctx *ctx)
{
int queued;
int err = ctx->err;
if (!ctx->queue.qlen) {
smp_mb__before_clear_bit();
clear_bit(CHAINIV_STATE_INUSE, &ctx->state);
if (!ctx->queue.qlen ||
test_and_set_bit(CHAINIV_STATE_INUSE, &ctx->state))
goto out;
}
queued = queue_work(kcrypto_wq, &ctx->postponed);
BUG_ON(!queued);
out:
return err;
}
static int async_chainiv_postpone_request(struct skcipher_givcrypt_request *req)
{
struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
struct async_chainiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
int err;
spin_lock_bh(&ctx->lock);
err = skcipher_enqueue_givcrypt(&ctx->queue, req);
spin_unlock_bh(&ctx->lock);
if (test_and_set_bit(CHAINIV_STATE_INUSE, &ctx->state))
return err;
ctx->err = err;
return async_chainiv_schedule_work(ctx);
}
static int async_chainiv_givencrypt_tail(struct skcipher_givcrypt_request *req)
{
struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
struct async_chainiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
struct ablkcipher_request *subreq = skcipher_givcrypt_reqctx(req);
unsigned int ivsize = crypto_ablkcipher_ivsize(geniv);
memcpy(req->giv, ctx->iv, ivsize);
memcpy(subreq->info, ctx->iv, ivsize);
ctx->err = crypto_ablkcipher_encrypt(subreq);
if (ctx->err)
goto out;
memcpy(ctx->iv, subreq->info, ivsize);
out:
return async_chainiv_schedule_work(ctx);
}
static int async_chainiv_givencrypt(struct skcipher_givcrypt_request *req)
{
struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
struct async_chainiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
struct ablkcipher_request *subreq = skcipher_givcrypt_reqctx(req);
ablkcipher_request_set_tfm(subreq, skcipher_geniv_cipher(geniv));
ablkcipher_request_set_callback(subreq, req->creq.base.flags,
req->creq.base.complete,
req->creq.base.data);
ablkcipher_request_set_crypt(subreq, req->creq.src, req->creq.dst,
req->creq.nbytes, req->creq.info);
if (test_and_set_bit(CHAINIV_STATE_INUSE, &ctx->state))
goto postpone;
if (ctx->queue.qlen) {
clear_bit(CHAINIV_STATE_INUSE, &ctx->state);
goto postpone;
}
return async_chainiv_givencrypt_tail(req);
postpone:
return async_chainiv_postpone_request(req);
}
static int async_chainiv_givencrypt_first(struct skcipher_givcrypt_request *req)
{
struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
struct async_chainiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
int err = 0;
if (test_and_set_bit(CHAINIV_STATE_INUSE, &ctx->state))
goto out;
if (crypto_ablkcipher_crt(geniv)->givencrypt !=
async_chainiv_givencrypt_first)
goto unlock;
crypto_ablkcipher_crt(geniv)->givencrypt = async_chainiv_givencrypt;
err = crypto_rng_get_bytes(crypto_default_rng, ctx->iv,
crypto_ablkcipher_ivsize(geniv));
unlock:
clear_bit(CHAINIV_STATE_INUSE, &ctx->state);
if (err)
return err;
out:
return async_chainiv_givencrypt(req);
}
static void async_chainiv_do_postponed(struct work_struct *work)
{
struct async_chainiv_ctx *ctx = container_of(work,
struct async_chainiv_ctx,
postponed);
struct skcipher_givcrypt_request *req;
struct ablkcipher_request *subreq;
int err;
/* Only handle one request at a time to avoid hogging keventd. */
spin_lock_bh(&ctx->lock);
req = skcipher_dequeue_givcrypt(&ctx->queue);
spin_unlock_bh(&ctx->lock);
if (!req) {
async_chainiv_schedule_work(ctx);
return;
}
subreq = skcipher_givcrypt_reqctx(req);
subreq->base.flags |= CRYPTO_TFM_REQ_MAY_SLEEP;
err = async_chainiv_givencrypt_tail(req);
local_bh_disable();
skcipher_givcrypt_complete(req, err);
local_bh_enable();
}
static int async_chainiv_init(struct crypto_tfm *tfm)
{
struct async_chainiv_ctx *ctx = crypto_tfm_ctx(tfm);
spin_lock_init(&ctx->lock);
crypto_init_queue(&ctx->queue, 100);
INIT_WORK(&ctx->postponed, async_chainiv_do_postponed);
return chainiv_init_common(tfm);
}
static void async_chainiv_exit(struct crypto_tfm *tfm)
{
struct async_chainiv_ctx *ctx = crypto_tfm_ctx(tfm);
BUG_ON(test_bit(CHAINIV_STATE_INUSE, &ctx->state) || ctx->queue.qlen);
skcipher_geniv_exit(tfm);
}
static struct crypto_template chainiv_tmpl;
static struct crypto_instance *chainiv_alloc(struct rtattr **tb)
{
struct crypto_attr_type *algt;
struct crypto_instance *inst;
int err;
algt = crypto_get_attr_type(tb);
err = PTR_ERR(algt);
if (IS_ERR(algt))
return ERR_PTR(err);
err = crypto_get_default_rng();
if (err)
return ERR_PTR(err);
inst = skcipher_geniv_alloc(&chainiv_tmpl, tb, 0, 0);
if (IS_ERR(inst))
goto put_rng;
inst->alg.cra_ablkcipher.givencrypt = chainiv_givencrypt_first;
inst->alg.cra_init = chainiv_init;
inst->alg.cra_exit = skcipher_geniv_exit;
inst->alg.cra_ctxsize = sizeof(struct chainiv_ctx);
if (!crypto_requires_sync(algt->type, algt->mask)) {
inst->alg.cra_flags |= CRYPTO_ALG_ASYNC;
inst->alg.cra_ablkcipher.givencrypt =
async_chainiv_givencrypt_first;
inst->alg.cra_init = async_chainiv_init;
inst->alg.cra_exit = async_chainiv_exit;
inst->alg.cra_ctxsize = sizeof(struct async_chainiv_ctx);
}
inst->alg.cra_ctxsize += inst->alg.cra_ablkcipher.ivsize;
out:
return inst;
put_rng:
crypto_put_default_rng();
goto out;
}
static void chainiv_free(struct crypto_instance *inst)
{
skcipher_geniv_free(inst);
crypto_put_default_rng();
}
static struct crypto_template chainiv_tmpl = {
.name = "chainiv",
.alloc = chainiv_alloc,
.free = chainiv_free,
.module = THIS_MODULE,
};
static int __init chainiv_module_init(void)
{
return crypto_register_template(&chainiv_tmpl);
}
static void chainiv_module_exit(void)
{
crypto_unregister_template(&chainiv_tmpl);
}
module_init(chainiv_module_init);
module_exit(chainiv_module_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Chain IV Generator");
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