On 02/20/2014 03:44 PM, Tejun Heo wrote:
PREPARE_[DELAYED_]WORK() are being phased out. They have few users
and a nasty surprise in terms of reentrancy guarantee as workqueue
considers work items to be different if they don't have the same work
function.
firewire core-device and sbp2 have been been multiplexing work items
with multiple work functions. Introduce fw_device_workfn() and
sbp2_lu_workfn() which invoke fw_device->workfn and
sbp2_logical_unit->workfn respectively and always use the two
functions as the work functions and update the users to set the
->workfn fields instead of overriding work functions using
PREPARE_DELAYED_WORK().
It would probably be best to route this with other related updates
through the workqueue tree.
Compile tested.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Stefan Richter <stefanr@xxxxxxxxxxxxxxxxx>
Cc: linux1394-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: Chris Boot <bootc@xxxxxxxxx>
Cc: linux-scsi@xxxxxxxxxxxxxxx
Cc: target-devel@xxxxxxxxxxxxxxx
---
drivers/firewire/core-device.c | 22 +++++++++++++++-------
drivers/firewire/sbp2.c | 17 +++++++++++++----
include/linux/firewire.h | 1 +
3 files changed, 29 insertions(+), 11 deletions(-)
diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
index de4aa40..2c6d5e1 100644
--- a/drivers/firewire/core-device.c
+++ b/drivers/firewire/core-device.c
@@ -916,7 +916,7 @@ static int lookup_existing_device(struct device *dev, void *data)
old->config_rom_retries = 0;
fw_notice(card, "rediscovered device %s\n", dev_name(dev));
- PREPARE_DELAYED_WORK(&old->work, fw_device_update);
+ old->workfn = fw_device_update;
fw_schedule_device_work(old, 0);
if (current_node == card->root_node)
@@ -1075,7 +1075,7 @@ static void fw_device_init(struct work_struct *work)
if (atomic_cmpxchg(&device->state,
FW_DEVICE_INITIALIZING,
FW_DEVICE_RUNNING) == FW_DEVICE_GONE) {
- PREPARE_DELAYED_WORK(&device->work, fw_device_shutdown);
+ device->workfn = fw_device_shutdown;
fw_schedule_device_work(device, SHUTDOWN_DELAY);
Implied mb of test_and_set_bit() in queue_work_on() ensures that the
newly assigned work function is visible on all cpus before evaluating
whether or not the work can be queued.
Ok.
} else {
fw_notice(card, "created device %s: GUID %08x%08x, S%d00\n",
@@ -1196,13 +1196,20 @@ static void fw_device_refresh(struct work_struct *work)
dev_name(&device->device), fw_rcode_string(ret));
gone:
atomic_set(&device->state, FW_DEVICE_GONE);
- PREPARE_DELAYED_WORK(&device->work, fw_device_shutdown);
+ device->workfn = fw_device_shutdown;
fw_schedule_device_work(device, SHUTDOWN_DELAY);
out:
if (node_id == card->root_node->node_id)
fw_schedule_bm_work(card, 0);
}
+static void fw_device_workfn(struct work_struct *work)
+{
+ struct fw_device *device = container_of(to_delayed_work(work),
+ struct fw_device, work);
I think this needs an smp_rmb() here.
+ device->workfn(work);
+}
+
Otherwise this cpu could speculatively load workfn before
set_work_pool_and_clear_pending(), which means that the old workfn
could have been loaded but PENDING was still set and caused queue_work_on()
to reject the work as already pending.
Result: the new work function never runs.
But this exposes a more general problem that I believe workqueue should
prevent; speculated loads and stores in the work item function should be
prevented from occurring before clearing PENDING in
set_work_pool_and_clear_pending().
IOW, the beginning of the work function should act like a barrier in
the same way that queue_work_on() (et. al.) already does.
Regards,
Peter Hurley
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