[dm-devel] [PATCH 2/6] dm crypt: Handle DM_CRYPT_NO_*_WORKQUEUE more explicit.

[Sebastian Andrzej Siewior]

By looking at the handling of DM_CRYPT_NO_*_WORKQUEUE in
kcryptd_queue_crypt() it appears that READ and WRITE requests might be
handled in the tasklet context as long as interrupts are disabled or it
is handled in hardirq context.

The WRITE requests should always be fed in preemptible context. There
are other requirements in the write path which sleep or acquire a mutex.

The READ requests should come from the storage driver, likely not in a
preemptible context. The source of the requests depends on the driver
and other factors like multiple queues in the block layer.

To simplify the handling of DM_CRYPT_NO_*_WORKQUEUE, handle READ
requests always in tasklet/softirq context since the requests will be
passed in hard or softirq context.
Handle the WRITE requests directly because they are already in
preemptible context and must not be passed to the taslket/softirq.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy at linutronix.de>
---
 drivers/md/dm-crypt.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 506655e5eecba..a498de3604a67 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -2215,30 +2215,22 @@ static void kcryptd_crypt_tasklet(struct tasklet_struct *t)
 {
 	struct dm_crypt_io *io = from_tasklet(io, t, tasklet);
 
-	if (bio_data_dir(io->base_bio) == READ)
-		kcryptd_crypt_read_convert(io);
-	else
-		kcryptd_crypt_write_convert(io);
+	kcryptd_crypt_read_convert(io);
 }
 
 static void kcryptd_queue_crypt(struct dm_crypt_io *io)
 {
 	struct crypt_config *cc = io->cc;
 
-	if ((bio_data_dir(io->base_bio) == READ && test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags)) ||
-	    (bio_data_dir(io->base_bio) == WRITE && test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags))) {
-		/*
-		 * in_irq(): Crypto API's skcipher_walk_first() refuses to work in hard IRQ context.
-		 * irqs_disabled(): the kernel may run some IO completion from the idle thread, but
-		 * it is being executed with irqs disabled.
-		 */
-		if (in_irq() || irqs_disabled()) {
-			tasklet_setup(&io->tasklet, kcryptd_crypt_tasklet);
-			tasklet_schedule(&io->tasklet);
-			return;
-		}
+	if (bio_data_dir(io->base_bio) == READ &&
+	    test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags)) {
+		tasklet_setup(&io->tasklet, kcryptd_crypt_tasklet);
+		tasklet_schedule(&io->tasklet);
+		return;
 
-		kcryptd_crypt(&io->work);
+	} else if (bio_data_dir(io->base_bio) == WRITE &&
+		   test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags)) {
+		kcryptd_crypt_write_convert(io);
 		return;
 	}
 
-- 
2.30.0