Re: [PATCH 6.6] Revert "dm-crypt, dm-verity: disable tasklets"

[Mikulas Patocka]

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@xxxxxxx/T/
> [2] https://lore.kernel.org/all/4d331659-badd-749d-fba1-271543631a8a@xxxxxxxxxx/

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@xxxxxxxxxx>
> ---
>  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
>