Re: [PATCH 1/1] EDAC: fix edac core deadlock when removing a device
From: Harry Ciao
Date: Mon Dec 22 2008 - 22:06:39 EST
Hi Andrew,
Thanks for your response!
I think the change to edac_device_workq_function() is necessary, because
edac_device_workq_teardown()'s call to cancel_delayed_work() won't
ensure that the work won't be running, that's why it has to go on to
call flush_workqueue() when cancel_delayed_work() returns zero, when the
work has been added to edac_workqueue already, so the whole
edac_workqueue has to be flushed to make sure this work completes before
the edac device it belongs to could be safely removed.
I also add a printk to edac_device_workq_function():
static void edac_device_workq_function(struct work_struct *work_req)
{
struct delayed_work *d_work = (struct delayed_work *)work_req;
struct edac_device_ctl_info *edac_dev = to_edac_device_ctl_work(d_work);
mutex_lock(&device_ctls_mutex);
/* If we are being removed, bail out immediately */
if (edac_dev->op_state == OP_OFFLINE) {
printk(KERN_CRIT "+++HARRY+++ edac device is being removed, bail out
from work!\n");
mutex_unlock(&device_ctls_mutex);
return;
}
/* Only poll controllers that are running polled and have a check */
if ((edac_dev->op_state == OP_RUNNING_POLL) &&
(edac_dev->edac_check != NULL)) {
edac_dev->edac_check(edac_dev);
}
mutex_unlock(&device_ctls_mutex);
...
and do a test to run pairs of insmod/rmmod about 10 times, as you could
see from below logs that 2/10 chances that the work is running by
edac_poller worker thread:
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
+++HARRY+++ edac device is being removed, bail out from work!
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
+++HARRY+++ edac device is being removed, bail out from work!
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
root@localhost:/root> insmod mv64x60_edac.ko
root@localhost:/root> rmmod mv64x60_edac.ko
root@localhost:/root>
So edac_device_workq_function() should bail out immediately if the edac
device that current work belongs to is being removed.
Best regards and Merry Chrismas!
Harry
Andrew Morton åé:
On Thu, 18 Dec 2008 13:09:18 +0800
Harry Ciao <qingtao.cao@xxxxxxxxxxxxx> wrote:
To remove an edac device, all pending work must be complete. At that point,
it is safe to remove the edac_dev structure.
If the pending work is not properly cleared and proper care is not taken
when waiting for it's completion, the following stack trace result:
...
--- a/drivers/edac/edac_device.c
+++ b/drivers/edac/edac_device.c
@@ -394,6 +394,12 @@ static void edac_device_workq_function(struct work_struct *work_req)
mutex_lock(&device_ctls_mutex);
+ /* If we are being removed, bail out immediately */
+ if (edac_dev->op_state == OP_OFFLINE) {
+ mutex_unlock(&device_ctls_mutex);
+ return;
+ }
+
/* Only poll controllers that are running polled and have a check */
if ((edac_dev->op_state == OP_RUNNING_POLL) &&
(edac_dev->edac_check != NULL)) {
@@ -585,14 +591,14 @@ struct edac_device_ctl_info *edac_device_del_device(struct device *dev)
/* mark this instance as OFFLINE */
edac_dev->op_state = OP_OFFLINE;
- /* clear workq processing on this instance */
- edac_device_workq_teardown(edac_dev);
-
/* deregister from global list */
del_edac_device_from_global_list(edac_dev);
mutex_unlock(&device_ctls_mutex);
+ /* clear workq processing on this instance */
+ edac_device_workq_teardown(edac_dev);
+
/* Tear down the sysfs entries for this instance */
edac_device_remove_sysfs(edac_dev);
Is the change to edac_device_workq_function() necessary?
edac_device_workq_teardown()'s call to cancel_delayed_work() will
ensure that edac_device_workq_function() isn't running.
Incidentally, edac_device_workq_teardown() is an open-coded
cancel_delayed_work_sync().
--
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