softirq: fix tasklet_kill() usage and users

Semantically the expectation from the tasklet init/kill API should be as below.

tasklet_init() == Init and Enable scheduling tasklet_kill() == Disable scheduling and Destroy

tasklet_init() API exibit above behavior but not the tasklet_kill(). The tasklet handler can still get scheduled and run even after the tasklet_kill().

There are 2, 3 places where drivers are working around this issue by calling tasklet_disable() which will add an usecount and there by avoiding the handlers being called. One of the example 'commit 1e1257860fd1 ("tty/serial: at91: correct the usage of tasklet")'

tasklet_enable/tasklet_disable is a pair API and expected to be used together. Usage of tasklet_disable() *just* to workround tasklet scheduling after kill is probably not the correct and inteded use of the API as done the API. We also happen to see similar issue where in shutdown path the tasklet_handler was getting called even after the tasklet_kill().

We can fix this be making sure tasklet_kill() does right thing and there by ensuring tasklet handler won't run after tasklet_kil() with very simple change. Patch fixes the tasklet code and also few drivers hacks to workaround the issue.

Cc Greg Kroah-Hartman <[email protected]>

Cc Andrew Morton <[email protected]>

Cc Thomas Gleixner <[email protected]>

Cc Tadeusz Struk <[email protected]>

Cc Herbert Xu <[email protected]>

Cc "David S. Miller" <[email protected]>

Cc Paul Bolle <[email protected]>

Cc Nicolas Ferre <[email protected]>

Signed-off-by Santosh Shilimkar <[email protected]>

---
 drivers/crypto/qat/qat_common/adf_isr.c    | 1 -
 drivers/crypto/qat/qat_common/adf_sriov.c  | 1 -
 drivers/crypto/qat/qat_common/adf_vf_isr.c | 2 --
 drivers/isdn/gigaset/interface.c           | 1 -
 drivers/tty/serial/atmel_serial.c          | 1 -
 kernel/softirq.c                           | 7 ++++---
 6 files changed, 4 insertions(+), 9 deletions(-)

drivers/crypto/qat/qat_common/adf_isr.c +0 -1

index 06d4901..fd5e900 100644
@@ -296,7 +296,6 @@ static void adf_cleanup_bh(struct adf_accel_dev *accel_dev)
 	int i;
 
 	for (i = 0; i < hw_data->num_banks; i++) {
-		tasklet_disable(&priv_data->banks[i].resp_handler);
 		tasklet_kill(&priv_data->banks[i].resp_handler);
 	}
 }

drivers/crypto/qat/qat_common/adf_sriov.c +0 -1

index 4a526e2..9e65888 100644
@@ -204,7 +204,6 @@ void adf_disable_sriov(struct adf_accel_dev *accel_dev)
 	}
 
 	for (i = 0, vf = accel_dev->pf.vf_info; i < totalvfs; i++, vf++) {
-		tasklet_disable(&vf->vf2pf_bh_tasklet);
 		tasklet_kill(&vf->vf2pf_bh_tasklet);
 		mutex_destroy(&vf->pf2vf_lock);
 	}

drivers/crypto/qat/qat_common/adf_vf_isr.c +0 -2

index aa689ca..81e63bf 100644
@@ -191,7 +191,6 @@ static int adf_setup_pf2vf_bh(struct adf_accel_dev *accel_dev)
 
 static void adf_cleanup_pf2vf_bh(struct adf_accel_dev *accel_dev)
 {
-	tasklet_disable(&accel_dev->vf.pf2vf_bh_tasklet);
 	tasklet_kill(&accel_dev->vf.pf2vf_bh_tasklet);
 	mutex_destroy(&accel_dev->vf.vf2pf_lock);
 }

@@ -268,7 +267,6 @@ static void adf_cleanup_bh(struct adf_accel_dev *accel_dev)
 {
 	struct adf_etr_data *priv_data = accel_dev->transport;
 
-	tasklet_disable(&priv_data->banks[0].resp_handler);
 	tasklet_kill(&priv_data->banks[0].resp_handler);
 }
 

drivers/isdn/gigaset/interface.c +0 -1

index 600c79b..2ce63b6 100644
@@ -524,7 +524,6 @@ void gigaset_if_free(struct cardstate *cs)
 	if (!drv->have_tty)
 		return;
 
-	tasklet_disable(&cs->if_wake_tasklet);
 	tasklet_kill(&cs->if_wake_tasklet);
 	cs->tty_dev = NULL;
 	tty_unregister_device(drv->tty, cs->minor_index);

drivers/tty/serial/atmel_serial.c +0 -1

index 954941d..27e638e 100644
@@ -1915,7 +1915,6 @@ static void atmel_shutdown(struct uart_port *port)
 	 * Clear out any scheduled tasklets before
 	 * we destroy the buffers
 	 */
-	tasklet_disable(&atmel_port->tasklet);
 	tasklet_kill(&atmel_port->tasklet);
 
 	/*

kernel/softirq.c +4 -3

index 17caf4b..21397eb 100644
@@ -498,7 +498,7 @@ static void tasklet_action(struct softirq_action *a)
 		list = list->next;
 
 		if (tasklet_trylock(t)) {
-			if (!atomic_read(&t->count)) {
+			if (atomic_read(&t->count) == 1) {
 				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
 							&t->state))
 					BUG();

@@ -534,7 +534,7 @@ static void tasklet_hi_action(struct softirq_action *a)
 		list = list->next;
 
 		if (tasklet_trylock(t)) {
-			if (!atomic_read(&t->count)) {
+			if (atomic_read(&t->count) == 1) {
 				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
 							&t->state))
 					BUG();

@@ -559,7 +559,7 @@ void tasklet_init(struct tasklet_struct *t,
 {
 	t->next = NULL;
 	t->state = 0;
-	atomic_set(&t->count, 0);
+	atomic_set(&t->count, 1);
 	t->func = func;
 	t->data = data;
 }

@@ -576,6 +576,7 @@ void tasklet_kill(struct tasklet_struct *t)
 		} while (test_bit(TASKLET_STATE_SCHED, &t->state));
 	}
 	tasklet_unlock_wait(t);
+	atomic_dec(&t->count);
 	clear_bit(TASKLET_STATE_SCHED, &t->state);
 }
 EXPORT_SYMBOL(tasklet_kill);

ping !!

Quoted 1 line · Santosh Shilimkar

ping !!

ping on a "RFC" after only 5 days in the middle of the merge window? That's bold...

Personally, I rarely respond to RFC patches as obviously the submitter doesn't think they solve the issue at hand :)