[PATCH v2 1/2] hyperv: Convert from tasklet to BH workqueue

From: Allen Pais
Date: Wed Apr 03 2024 - 12:56:43 EST

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 drivers/hv/* from tasklet to BH workqueue.

Based on the work done by Tejun Heo <tj@xxxxxxxxxx>
Branch: https://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git for-6.10

Signed-off-by: Allen Pais <allen.lkml@xxxxxxxxx>
---
drivers/hv/channel.c | 8 ++++----
drivers/hv/channel_mgmt.c | 5 ++---
drivers/hv/connection.c | 9 +++++----
drivers/hv/hv.c | 3 +--
drivers/hv/hv_balloon.c | 4 ++--
drivers/hv/hv_fcopy.c | 8 ++++----
drivers/hv/hv_kvp.c | 8 ++++----
drivers/hv/hv_snapshot.c | 8 ++++----
drivers/hv/hyperv_vmbus.h | 9 +++++----
drivers/hv/vmbus_drv.c | 20 +++++++++++---------
include/linux/hyperv.h | 2 +-
11 files changed, 43 insertions(+), 41 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index adbf674355b2..876d78eb4dce 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -859,7 +859,7 @@ void vmbus_reset_channel_cb(struct vmbus_channel *channel)
unsigned long flags;

/*
- * vmbus_on_event(), running in the per-channel tasklet, can race
+ * vmbus_on_event(), running in the per-channel work, can race
* with vmbus_close_internal() in the case of SMP guest, e.g., when
* the former is accessing channel->inbound.ring_buffer, the latter
* could be freeing the ring_buffer pages, so here we must stop it
@@ -871,7 +871,7 @@ void vmbus_reset_channel_cb(struct vmbus_channel *channel)
* and that the channel ring buffer is no longer being accessed, cf.
* the calls to napi_disable() in netvsc_device_remove().
*/
- tasklet_disable(&channel->callback_event);
+ disable_work_sync(&channel->callback_event);

/* See the inline comments in vmbus_chan_sched(). */
spin_lock_irqsave(&channel->sched_lock, flags);
@@ -880,8 +880,8 @@ void vmbus_reset_channel_cb(struct vmbus_channel *channel)

channel->sc_creation_callback = NULL;

- /* Re-enable tasklet for use on re-open */
- tasklet_enable(&channel->callback_event);
+ /* Re-enable work for use on re-open */
+ enable_and_queue_work(system_bh_wq, &channel->callback_event);
}

static int vmbus_close_internal(struct vmbus_channel *channel)
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 2f4d09ce027a..58397071a0de 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -353,8 +353,7 @@ static struct vmbus_channel *alloc_channel(void)

INIT_LIST_HEAD(&channel->sc_list);

- tasklet_init(&channel->callback_event,
- vmbus_on_event, (unsigned long)channel);
+ INIT_WORK(&channel->callback_event, vmbus_on_event);

hv_ringbuffer_pre_init(channel);

@@ -366,7 +365,7 @@ static struct vmbus_channel *alloc_channel(void)
*/
static void free_channel(struct vmbus_channel *channel)
{
- tasklet_kill(&channel->callback_event);
+ cancel_work_sync(&channel->callback_event);
vmbus_remove_channel_attr_group(channel);

kobject_put(&channel->kobj);
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 3cabeeabb1ca..f2a3394a8303 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -372,12 +372,13 @@ struct vmbus_channel *relid2channel(u32 relid)
* 3. Once we return, enable signaling from the host. Once this
* state is set we check to see if additional packets are
* available to read. In this case we repeat the process.
- * If this tasklet has been running for a long time
+ * If this work has been running for a long time
* then reschedule ourselves.
*/
-void vmbus_on_event(unsigned long data)
+void vmbus_on_event(struct work_struct *t)
{
- struct vmbus_channel *channel = (void *) data;
+ struct vmbus_channel *channel = from_work(channel, t,
+ callback_event);
void (*callback_fn)(void *context);

trace_vmbus_on_event(channel);
@@ -401,7 +402,7 @@ void vmbus_on_event(unsigned long data)
return;

hv_begin_read(&channel->inbound);
- tasklet_schedule(&channel->callback_event);
+ queue_work(system_bh_wq, &channel->callback_event);
}

/*
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index a8ad728354cb..2af92f08f9ce 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -119,8 +119,7 @@ int hv_synic_alloc(void)
for_each_present_cpu(cpu) {
hv_cpu = per_cpu_ptr(hv_context.cpu_context, cpu);

- tasklet_init(&hv_cpu->msg_dpc,
- vmbus_on_msg_dpc, (unsigned long) hv_cpu);
+ INIT_WORK(&hv_cpu->msg_dpc, vmbus_on_msg_dpc);

if (ms_hyperv.paravisor_present && hv_isolation_type_tdx()) {
hv_cpu->post_msg_page = (void *)get_zeroed_page(GFP_ATOMIC);
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index e000fa3b9f97..c7efa2ff4cdf 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -2083,7 +2083,7 @@ static int balloon_suspend(struct hv_device *hv_dev)
{
struct hv_dynmem_device *dm = hv_get_drvdata(hv_dev);

- tasklet_disable(&hv_dev->channel->callback_event);
+ disable_work_sync(&hv_dev->channel->callback_event);

cancel_work_sync(&dm->balloon_wrk.wrk);
cancel_work_sync(&dm->ha_wrk.wrk);
@@ -2094,7 +2094,7 @@ static int balloon_suspend(struct hv_device *hv_dev)
vmbus_close(hv_dev->channel);
}

- tasklet_enable(&hv_dev->channel->callback_event);
+ enable_and_queue_work(system_bh_wq, &hv_dev->channel->callback_event);

return 0;

diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
index 922d83eb7ddf..fd6799293c17 100644
--- a/drivers/hv/hv_fcopy.c
+++ b/drivers/hv/hv_fcopy.c
@@ -71,7 +71,7 @@ static void fcopy_poll_wrapper(void *channel)
{
/* Transaction is finished, reset the state here to avoid races. */
fcopy_transaction.state = HVUTIL_READY;
- tasklet_schedule(&((struct vmbus_channel *)channel)->callback_event);
+ queue_work(system_bh_wq, &((struct vmbus_channel *)channel)->callback_event);
}

static void fcopy_timeout_func(struct work_struct *dummy)
@@ -391,7 +391,7 @@ int hv_fcopy_pre_suspend(void)
if (!fcopy_msg)
return -ENOMEM;

- tasklet_disable(&channel->callback_event);
+ disable_work_sync(&channel->callback_event);

fcopy_msg->operation = CANCEL_FCOPY;

@@ -404,7 +404,7 @@ int hv_fcopy_pre_suspend(void)

fcopy_transaction.state = HVUTIL_READY;

- /* tasklet_enable() will be called in hv_fcopy_pre_resume(). */
+ /* enable_and_queue_work(system_bh_wq, ) will be called in hv_fcopy_pre_resume(). */
return 0;
}

@@ -412,7 +412,7 @@ int hv_fcopy_pre_resume(void)
{
struct vmbus_channel *channel = fcopy_transaction.recv_channel;

- tasklet_enable(&channel->callback_event);
+ enable_and_queue_work(system_bh_wq, &channel->callback_event);

return 0;
}
diff --git a/drivers/hv/hv_kvp.c b/drivers/hv/hv_kvp.c
index d35b60c06114..85b8fb4a3d2e 100644
--- a/drivers/hv/hv_kvp.c
+++ b/drivers/hv/hv_kvp.c
@@ -113,7 +113,7 @@ static void kvp_poll_wrapper(void *channel)
{
/* Transaction is finished, reset the state here to avoid races. */
kvp_transaction.state = HVUTIL_READY;
- tasklet_schedule(&((struct vmbus_channel *)channel)->callback_event);
+ queue_work(system_bh_wq, &((struct vmbus_channel *)channel)->callback_event);
}

static void kvp_register_done(void)
@@ -160,7 +160,7 @@ static void kvp_timeout_func(struct work_struct *dummy)

static void kvp_host_handshake_func(struct work_struct *dummy)
{
- tasklet_schedule(&kvp_transaction.recv_channel->callback_event);
+ queue_work(system_bh_wq, &kvp_transaction.recv_channel->callback_event);
}

static int kvp_handle_handshake(struct hv_kvp_msg *msg)
@@ -786,7 +786,7 @@ int hv_kvp_pre_suspend(void)
{
struct vmbus_channel *channel = kvp_transaction.recv_channel;

- tasklet_disable(&channel->callback_event);
+ disable_work_sync(&channel->callback_event);

/*
* If there is a pending transtion, it's unnecessary to tell the host
@@ -809,7 +809,7 @@ int hv_kvp_pre_resume(void)
{
struct vmbus_channel *channel = kvp_transaction.recv_channel;

- tasklet_enable(&channel->callback_event);
+ enable_and_queue_work(system_bh_wq, &channel->callback_event);

return 0;
}
diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index 0d2184be1691..46c2263d2591 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -83,7 +83,7 @@ static void vss_poll_wrapper(void *channel)
{
/* Transaction is finished, reset the state here to avoid races. */
vss_transaction.state = HVUTIL_READY;
- tasklet_schedule(&((struct vmbus_channel *)channel)->callback_event);
+ queue_work(system_bh_wq, &((struct vmbus_channel *)channel)->callback_event);
}

/*
@@ -421,7 +421,7 @@ int hv_vss_pre_suspend(void)
if (!vss_msg)
return -ENOMEM;

- tasklet_disable(&channel->callback_event);
+ disable_work_sync(&channel->callback_event);

vss_msg->vss_hdr.operation = VSS_OP_THAW;

@@ -435,7 +435,7 @@ int hv_vss_pre_suspend(void)

vss_transaction.state = HVUTIL_READY;

- /* tasklet_enable() will be called in hv_vss_pre_resume(). */
+ /* enable_and_queue_work() will be called in hv_vss_pre_resume(). */
return 0;
}

@@ -443,7 +443,7 @@ int hv_vss_pre_resume(void)
{
struct vmbus_channel *channel = vss_transaction.recv_channel;

- tasklet_enable(&channel->callback_event);
+ enable_and_queue_work(system_bh_wq, &channel->callback_event);

return 0;
}
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index f6b1e710f805..95ca570ac7af 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -19,6 +19,7 @@
#include <linux/atomic.h>
#include <linux/hyperv.h>
#include <linux/interrupt.h>
+#include <linux/workqueue.h>

#include "hv_trace.h"

@@ -136,10 +137,10 @@ struct hv_per_cpu_context {

/*
* Starting with win8, we can take channel interrupts on any CPU;
- * we will manage the tasklet that handles events messages on a per CPU
+ * we will manage the work that handles events messages on a per CPU
* basis.
*/
- struct tasklet_struct msg_dpc;
+ struct work_struct msg_dpc;
};

struct hv_context {
@@ -366,8 +367,8 @@ void vmbus_disconnect(void);

int vmbus_post_msg(void *buffer, size_t buflen, bool can_sleep);

-void vmbus_on_event(unsigned long data);
-void vmbus_on_msg_dpc(unsigned long data);
+void vmbus_on_event(struct work_struct *t);
+void vmbus_on_msg_dpc(struct work_struct *t);

int hv_kvp_init(struct hv_util_service *srv);
void hv_kvp_deinit(void);
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 4cb17603a828..28490068cacc 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1025,9 +1025,9 @@ static void vmbus_onmessage_work(struct work_struct *work)
kfree(ctx);
}

-void vmbus_on_msg_dpc(unsigned long data)
+void vmbus_on_msg_dpc(struct work_struct *t)
{
- struct hv_per_cpu_context *hv_cpu = (void *)data;
+ struct hv_per_cpu_context *hv_cpu = from_work(hv_cpu, t, msg_dpc);
void *page_addr = hv_cpu->synic_message_page;
struct hv_message msg_copy, *msg = (struct hv_message *)page_addr +
VMBUS_MESSAGE_SINT;
@@ -1131,7 +1131,7 @@ void vmbus_on_msg_dpc(unsigned long data)
* before sending the rescind message of the same
* channel. These messages are sent to the guest's
* connect CPU; the guest then starts processing them
- * in the tasklet handler on this CPU:
+ * in the work handler on this CPU:
*
* VMBUS_CONNECT_CPU
*
@@ -1276,7 +1276,7 @@ static void vmbus_chan_sched(struct hv_per_cpu_context *hv_cpu)
hv_begin_read(&channel->inbound);
fallthrough;
case HV_CALL_DIRECT:
- tasklet_schedule(&channel->callback_event);
+ queue_work(system_bh_wq, &channel->callback_event);
}

sched_unlock:
@@ -1304,7 +1304,7 @@ static void vmbus_isr(void)
hv_stimer0_isr();
vmbus_signal_eom(msg, HVMSG_TIMER_EXPIRED);
} else
- tasklet_schedule(&hv_cpu->msg_dpc);
+ queue_work(system_bh_wq, &hv_cpu->msg_dpc);
}

add_interrupt_randomness(vmbus_interrupt);
@@ -2371,10 +2371,12 @@ static int vmbus_bus_suspend(struct device *dev)
hv_context.cpu_context, VMBUS_CONNECT_CPU);
struct vmbus_channel *channel, *sc;

- tasklet_disable(&hv_cpu->msg_dpc);
+ disable_work_sync(&hv_cpu->msg_dpc);
vmbus_connection.ignore_any_offer_msg = true;
- /* The tasklet_enable() takes care of providing a memory barrier */
- tasklet_enable(&hv_cpu->msg_dpc);
+ /* The enable_and_queue_work() takes care of
+ * providing a memory barrier
+ */
+ enable_and_queue_work(system_bh_wq, &hv_cpu->msg_dpc);

/* Drain all the workqueues as we are in suspend */
drain_workqueue(vmbus_connection.rescind_work_queue);
@@ -2692,7 +2694,7 @@ static void __exit vmbus_exit(void)
struct hv_per_cpu_context *hv_cpu
= per_cpu_ptr(hv_context.cpu_context, cpu);

- tasklet_kill(&hv_cpu->msg_dpc);
+ cancel_work_sync(&hv_cpu->msg_dpc);
}
hv_debug_rm_all_dir();

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 6ef0557b4bff..db3d85ea5ce6 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -882,7 +882,7 @@ struct vmbus_channel {
bool out_full_flag;

/* Channel callback's invoked in softirq context */
- struct tasklet_struct callback_event;
+ struct work_struct callback_event;
void (*onchannel_callback)(void *context);
void *channel_callback_context;

--
2.17.1