Received-SPF: pass (google.com: domain of linux-kernel+bounces-141802-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Message-ID: <4e5e4634-a2d0-ce35-3884-829d385c0879@huawei.com>
Date: Fri, 12 Apr 2024 10:06:14 +0800
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:104.0) Gecko/20100101
 Thunderbird/104.0
Subject: Re: [PATCH 6.6] Revert "dm-crypt, dm-verity: disable tasklets"
To: Mikulas Patocka <mpatocka@redhat.com>
CC: <stable@vger.kernel.org>, <gregkh@linuxfoundation.org>,
	<torvalds@linux-foundation.org>, <tglx@linutronix.de>,
	<linux-kernel@vger.kernel.org>, <dm-devel@lists.linux.dev>,
	<msnitzer@redhat.com>, <ignat@cloudflare.com>, <damien.lemoal@wdc.com>,
	<houtao1@huawei.com>, <nhuck@google.com>, <peterz@infradead.org>,
	<yukuai3@huawei.com>, <yangerkun@huawei.com>, <yi.zhang@huawei.com>,
	<lilingfeng@huaweicloud.com>
References: <20240411091539.361470-1-lilingfeng3@huawei.com>
 <7c17f31a-2cc3-1597-e2b5-832355de7647@redhat.com>
From: Li Lingfeng <lilingfeng3@huawei.com>
In-Reply-To: <7c17f31a-2cc3-1597-e2b5-832355de7647@redhat.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 8bit

Hi

I'm having difficulty understanding "Workqueues and ksoftirqd may be 
scheduled arbitrarily".
This is my understanding:
kcryptd_queue_crypt
  tasklet_schedule
   __tasklet_schedule
    __tasklet_schedule_common
     raise_softirq_irqoff
      wakeup_softirqd
       wake_up_process // ksoftirqd

run_ksoftirqd
  __do_softirq
   softirq_handle_begin
    __local_bh_disable_ip // Turn off preemption
<---------- [1] ---------->
   tasklet_action // h->action
    tasklet_action_common
     tasklet_trylock
      kcryptd_crypt_tasklet // t->func(t->data)
      ...
       queue_work(cc->io_queue, &io->work)
<---------- [2] ---------->
     tasklet_unlock

// workqueue process
kcryptd_io_bio_endio
  ...
  // free tasklet_struct

Since preemption has been turned off at [1], I'm confused about how the 
CPU can be scheduled out to do work first at [2].
Would you mind explaining it to me?

Thanks

在 2024/4/11 20:37, Mikulas Patocka 写道:
> Hi
>
> I NACK this.
>
>
> On Thu, 11 Apr 2024, Li Lingfeng wrote:
>
>> This reverts commit 5735a2671ffb70ea29ca83969fe01316ee2ed6fc which is
>> commit 0a9bab391e336489169b95cb0d4553d921302189 upstream.
>>
>> Tasklet is thought to cause memory corruption [1], so it was disabled in
>> dm-crypt and dm-verity. However, memory corruption may not happen since
>> cc->io_queue is created without WQ_UNBOUND [2].
>> Revert commit 5735a2671ffb ("dm-crypt, dm-verity: disable tasklets") to
>> bring tasklet back.
>>
>> [1] https://lore.kernel.org/all/d390d7ee-f142-44d3-822a-87949e14608b@suse.de/T/
>> [2] https://lore.kernel.org/all/4d331659-badd-749d-fba1-271543631a8a@huawei.com/
> Regarding [2] - if you add mdelay, you can make the race condition less
> reproducible, but it is not a proper fix and the race condition stays
> there unfixed.
>
> Workqueues and ksoftirqd may be scheduled arbitrarily, there is no
> guarantee that they will be executed in a particular order, even if they
> are executed on the same CPU.
>
> Mikulas
>
>> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
>> ---
>>   drivers/md/dm-crypt.c         | 38 +++++++++++++++++++++++++++++++++--
>>   drivers/md/dm-verity-target.c | 26 ++++++++++++++++++++++--
>>   drivers/md/dm-verity.h        |  1 +
>>   3 files changed, 61 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
>> index aa6bb5b4704b..a60d91d02e28 100644
>> --- a/drivers/md/dm-crypt.c
>> +++ b/drivers/md/dm-crypt.c
>> @@ -75,8 +75,10 @@ struct dm_crypt_io {
>>   	struct bio *base_bio;
>>   	u8 *integrity_metadata;
>>   	bool integrity_metadata_from_pool:1;
>> +	bool in_tasklet:1;
>>   
>>   	struct work_struct work;
>> +	struct tasklet_struct tasklet;
>>   
>>   	struct convert_context ctx;
>>   
>> @@ -1775,6 +1777,7 @@ static void crypt_io_init(struct dm_crypt_io *io, struct crypt_config *cc,
>>   	io->ctx.r.req = NULL;
>>   	io->integrity_metadata = NULL;
>>   	io->integrity_metadata_from_pool = false;
>> +	io->in_tasklet = false;
>>   	atomic_set(&io->io_pending, 0);
>>   }
>>   
>> @@ -1785,6 +1788,13 @@ static void crypt_inc_pending(struct dm_crypt_io *io)
>>   
>>   static void kcryptd_queue_read(struct dm_crypt_io *io);
>>   
>> +static void kcryptd_io_bio_endio(struct work_struct *work)
>> +{
>> +	struct dm_crypt_io *io = container_of(work, struct dm_crypt_io, work);
>> +
>> +	bio_endio(io->base_bio);
>> +}
>> +
>>   /*
>>    * One of the bios was finished. Check for completion of
>>    * the whole request and correctly clean up the buffer.
>> @@ -1817,6 +1827,20 @@ static void crypt_dec_pending(struct dm_crypt_io *io)
>>   
>>   	base_bio->bi_status = error;
>>   
>> +	/*
>> +	 * If we are running this function from our tasklet,
>> +	 * we can't call bio_endio() here, because it will call
>> +	 * clone_endio() from dm.c, which in turn will
>> +	 * free the current struct dm_crypt_io structure with
>> +	 * our tasklet. In this case we need to delay bio_endio()
>> +	 * execution to after the tasklet is done and dequeued.
>> +	 */
>> +	if (io->in_tasklet) {
>> +		INIT_WORK(&io->work, kcryptd_io_bio_endio);
>> +		queue_work(cc->io_queue, &io->work);
>> +		return;
>> +	}
>> +
>>   	bio_endio(base_bio);
>>   }
>>   
>> @@ -2291,6 +2315,11 @@ static void kcryptd_crypt(struct work_struct *work)
>>   		kcryptd_crypt_write_convert(io);
>>   }
>>   
>> +static void kcryptd_crypt_tasklet(unsigned long work)
>> +{
>> +	kcryptd_crypt((struct work_struct *)work);
>> +}
>> +
>>   static void kcryptd_queue_crypt(struct dm_crypt_io *io)
>>   {
>>   	struct crypt_config *cc = io->cc;
>> @@ -2302,10 +2331,15 @@ static void kcryptd_queue_crypt(struct dm_crypt_io *io)
>>   		 * irqs_disabled(): the kernel may run some IO completion from the idle thread, but
>>   		 * it is being executed with irqs disabled.
>>   		 */
>> -		if (!(in_hardirq() || irqs_disabled())) {
>> -			kcryptd_crypt(&io->work);
>> +		if (in_hardirq() || irqs_disabled()) {
>> +			io->in_tasklet = true;
>> +			tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, (unsigned long)&io->work);
>> +			tasklet_schedule(&io->tasklet);
>>   			return;
>>   		}
>> +
>> +		kcryptd_crypt(&io->work);
>> +		return;
>>   	}
>>   
>>   	INIT_WORK(&io->work, kcryptd_crypt);
>> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
>> index 49e4a35d7019..0bb126eadc0d 100644
>> --- a/drivers/md/dm-verity-target.c
>> +++ b/drivers/md/dm-verity-target.c
>> @@ -701,6 +701,23 @@ static void verity_work(struct work_struct *w)
>>   	verity_finish_io(io, errno_to_blk_status(verity_verify_io(io)));
>>   }
>>   
>> +static void verity_tasklet(unsigned long data)
>> +{
>> +	struct dm_verity_io *io = (struct dm_verity_io *)data;
>> +	int err;
>> +
>> +	io->in_tasklet = true;
>> +	err = verity_verify_io(io);
>> +	if (err == -EAGAIN || err == -ENOMEM) {
>> +		/* fallback to retrying with work-queue */
>> +		INIT_WORK(&io->work, verity_work);
>> +		queue_work(io->v->verify_wq, &io->work);
>> +		return;
>> +	}
>> +
>> +	verity_finish_io(io, errno_to_blk_status(err));
>> +}
>> +
>>   static void verity_end_io(struct bio *bio)
>>   {
>>   	struct dm_verity_io *io = bio->bi_private;
>> @@ -713,8 +730,13 @@ static void verity_end_io(struct bio *bio)
>>   		return;
>>   	}
>>   
>> -	INIT_WORK(&io->work, verity_work);
>> -	queue_work(io->v->verify_wq, &io->work);
>> +	if (static_branch_unlikely(&use_tasklet_enabled) && io->v->use_tasklet) {
>> +		tasklet_init(&io->tasklet, verity_tasklet, (unsigned long)io);
>> +		tasklet_schedule(&io->tasklet);
>> +	} else {
>> +		INIT_WORK(&io->work, verity_work);
>> +		queue_work(io->v->verify_wq, &io->work);
>> +	}
>>   }
>>   
>>   /*
>> diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
>> index db93a91169d5..7e495cc375b0 100644
>> --- a/drivers/md/dm-verity.h
>> +++ b/drivers/md/dm-verity.h
>> @@ -87,6 +87,7 @@ struct dm_verity_io {
>>   	bool in_tasklet;
>>   
>>   	struct work_struct work;
>> +	struct tasklet_struct tasklet;
>>   
>>   	char *recheck_buffer;
>>   
>> -- 
>> 2.31.1
>>