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Message-ID: <7c17f31a-2cc3-1597-e2b5-832355de7647@redhat.com>
Date: Thu, 11 Apr 2024 14:37:48 +0200 (CEST)
From: Mikulas Patocka <mpatocka@...hat.com>
To: Li Lingfeng <lilingfeng3@...wei.com>
cc: stable@...r.kernel.org, gregkh@...uxfoundation.org,
torvalds@...ux-foundation.org, tglx@...utronix.de,
linux-kernel@...r.kernel.org, dm-devel@...ts.linux.dev,
msnitzer@...hat.com, ignat@...udflare.com, damien.lemoal@....com,
bob.liu@...cle.com, houtao1@...wei.com, nhuck@...gle.com,
peterz@...radead.org, mingo@...e.hu, yukuai3@...wei.com,
yangerkun@...wei.com, yi.zhang@...wei.com, lilingfeng@...weicloud.com
Subject: Re: [PATCH 6.6] Revert "dm-crypt, dm-verity: disable tasklets"
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@...wei.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
>
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