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Sender: Tejun Heo <htejun@gmail.com>
From: Tejun Heo <tj@kernel.org>
To: torvalds@linux-foundation.org,
	mpatocka@redhat.com
Cc: linux-kernel@vger.kernel.org,
	dm-devel@lists.linux.dev,
	msnitzer@redhat.com,
	ignat@cloudflare.com,
	damien.lemoal@wdc.com,
	bob.liu@oracle.com,
	houtao1@huawei.com,
	peterz@infradead.org,
	mingo@kernel.org,
	netdev@vger.kernel.org,
	allen.lkml@gmail.com,
	kernel-team@meta.com,
	Tejun Heo <tj@kernel.org>,
	Alasdair Kergon <agk@redhat.com>,
	Mike Snitzer <snitzer@kernel.org>
Subject: [PATCH 7/8] dm-crypt: Convert from tasklet to BH workqueue
Date: Mon, 29 Jan 2024 23:11:54 -1000
Message-ID: <20240130091300.2968534-8-tj@kernel.org>
In-Reply-To: <20240130091300.2968534-1-tj@kernel.org>
References: <20240130091300.2968534-1-tj@kernel.org>
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The only generic interface to execute asynchronously in the BH context is
tasklet; however, it's marked deprecated and has some design flaws. To
replace tasklets, BH workqueue support was recently added. A BH workqueue
behaves similarly to regular workqueues except that the queued work items
are executed in the BH context.

This patch converts dm-crypt from tasklet to BH workqueue.

Like a regular workqueue, a BH workqueue allows freeing the currently
executing work item. Converting from tasklet to BH workqueue removes the
need for deferring bio_endio() again to a work item, which was buggy anyway.

I tested this lightly with "--perf-no_read_workqueue
--perf-no_write_workqueue" + some code modifications, but would really
-appreciate if someone who knows the code base better could take a look.

Signed-off-by: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/82b964f0-c2c8-a2c6-5b1f-f3145dc2c8e5@redhat.com
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@kernel.org>
Cc: dm-devel@lists.linux.dev
---
 drivers/md/dm-crypt.c | 36 ++----------------------------------
 1 file changed, 2 insertions(+), 34 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 855b482cbff1..619c762d4072 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -73,11 +73,8 @@ 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;
 
 	atomic_t io_pending;
@@ -1762,7 +1759,6 @@ 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);
 }
 
@@ -1771,13 +1767,6 @@ static void crypt_inc_pending(struct dm_crypt_io *io)
 	atomic_inc(&io->io_pending);
 }
 
-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.
@@ -1800,21 +1789,6 @@ static void crypt_dec_pending(struct dm_crypt_io *io)
 		kfree(io->integrity_metadata);
 
 	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);
 }
 
@@ -2246,11 +2220,6 @@ 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;
@@ -2263,9 +2232,8 @@ static void kcryptd_queue_crypt(struct dm_crypt_io *io)
 		 * it is being executed with irqs disabled.
 		 */
 		if (in_hardirq() || irqs_disabled()) {
-			io->in_tasklet = true;
-			tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, (unsigned long)&io->work);
-			tasklet_schedule(&io->tasklet);
+			INIT_WORK(&io->work, kcryptd_crypt);
+			queue_work(system_bh_wq, &io->work);
 			return;
 		}
 
-- 
2.43.0