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Message-ID: <20131118181440.GA2996@google.com>
Date: Mon, 18 Nov 2013 11:14:40 -0700
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Tejun Heo <tj@...nel.org>
Cc: Hugh Dickins <hughd@...gle.com>,
Steven Rostedt <rostedt@...dmis.org>,
Li Zefan <lizefan@...wei.com>,
Markus Blank-Burian <burian@...nster.de>,
Michal Hocko <mhocko@...e.cz>,
Johannes Weiner <hannes@...xchg.org>,
David Rientjes <rientjes@...gle.com>,
Ying Han <yinghan@...gle.com>,
Greg Thelen <gthelen@...gle.com>,
Michel Lespinasse <walken@...gle.com>, cgroups@...r.kernel.org,
"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
Lai Jiangshan <laijs@...fujitsu.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Rafael J. Wysocki" <rjw@...k.pl>,
Alexander Duyck <alexander.h.duyck@...el.com>,
Yinghai Lu <yinghai@...nel.org>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: Possible regression with cgroups in 3.11
On Sat, Nov 16, 2013 at 01:53:56PM +0900, Tejun Heo wrote:
> Hello, Bjorn.
>
> On Fri, Nov 15, 2013 at 05:28:20PM -0700, Bjorn Helgaas wrote:
> > It would be better to fix PCI so we don't call VF driver .probe() methods
> > from inside a PF driver .probe() method, but that's a bigger project.
>
> Yeah, if pci doesn't need the recursion, we can simply revert restore
> the lockdep annoation on work_on_cpu().
>
> > @@ -293,7 +293,9 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
> > its local memory on the right node without any need to
> > change it. */
> > node = dev_to_node(&dev->dev);
> > - if (node >= 0) {
> > + preempt_disable();
> > +
> > + if (node >= 0 && node != numa_node_id()) {
>
> A bit of comment here would be nice but yeah I think this should work.
> Can you please also queue the revert of c2fda509667b ("workqueue:
> allow work_on_cpu() to be called recursively") after this patch?
> Please feel free to add my acked-by.
OK, below are the two patches (Alex's fix + the revert) I propose to
merge. Unless there are objections, I'll ask Linus to pull these
before v3.13-rc1.
Bjorn
commit 84f23f99b507c2c9247f47d3db0f71a3fd65e3a3
Author: Alexander Duyck <alexander.h.duyck@...el.com>
Date: Mon Nov 18 10:59:59 2013 -0700
PCI: Avoid unnecessary CPU switch when calling driver .probe() method
If we are already on a CPU local to the device, call the driver .probe()
method directly without using work_on_cpu().
This is a workaround for a lockdep warning in the following scenario:
pci_call_probe
work_on_cpu(cpu, local_pci_probe, ...)
driver .probe
pci_enable_sriov
...
pci_bus_add_device
...
pci_call_probe
work_on_cpu(cpu, local_pci_probe, ...)
It would be better to fix PCI so we don't call VF driver .probe() methods
from inside a PF driver .probe() method, but that's a bigger project.
[bhelgaas: disable preemption, open bugzilla, rework comments & changelog]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=65071
Link: http://lkml.kernel.org/r/CAE9FiQXYQEAZ=0sG6+2OdffBqfLS9MpoN1xviRR9aDbxPxcKxQ@mail.gmail.com
Link: http://lkml.kernel.org/r/20130624195942.40795.27292.stgit@ahduyck-cp1.jf.intel.com
Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Acked-by: Tejun Heo <tj@...nel.org>
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 9042fdbd7244..add04e70ac2a 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -288,12 +288,24 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
int error, node;
struct drv_dev_and_id ddi = { drv, dev, id };
- /* Execute driver initialization on node where the device's
- bus is attached to. This way the driver likely allocates
- its local memory on the right node without any need to
- change it. */
+ /*
+ * Execute driver initialization on node where the device is
+ * attached. This way the driver likely allocates its local memory
+ * on the right node.
+ */
node = dev_to_node(&dev->dev);
- if (node >= 0) {
+ preempt_disable();
+
+ /*
+ * On NUMA systems, we are likely to call a PF probe function using
+ * work_on_cpu(). If that probe calls pci_enable_sriov() (which
+ * adds the VF devices via pci_bus_add_device()), we may re-enter
+ * this function to call the VF probe function. Calling
+ * work_on_cpu() again will cause a lockdep warning. Since VFs are
+ * always on the same node as the PF, we can work around this by
+ * avoiding work_on_cpu() when we're already on the correct node.
+ */
+ if (node >= 0 && node != numa_node_id()) {
int cpu;
get_online_cpus();
@@ -305,6 +317,8 @@ static int pci_call_probe(struct pci_driver *drv, struct pci_dev *dev,
put_online_cpus();
} else
error = local_pci_probe(&ddi);
+
+ preempt_enable();
return error;
}
commit 2dde5285d06370b2004613ee4fd253e95622af20
Author: Bjorn Helgaas <bhelgaas@...gle.com>
Date: Mon Nov 18 11:00:29 2013 -0700
Revert "workqueue: allow work_on_cpu() to be called recursively"
This reverts commit c2fda509667b0fda4372a237f5a59ea4570b1627.
c2fda509667b removed lockdep annotation from work_on_cpu() to work around
the PCI path that calls work_on_cpu() from within a work_on_cpu() work item
(PF driver .probe() method -> pci_enable_sriov() -> add VFs -> VF driver
.probe method).
84f23f99b507 ("PCI: Avoid unnecessary CPU switch when calling driver
.probe() method) avoids that recursive work_on_cpu() use in a different
way, so this revert restores the work_on_cpu() lockdep annotation.
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Acked-by: Tejun Heo <tj@...nel.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 987293d03ebc..5690b8eabfbc 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2840,19 +2840,6 @@ already_gone:
return false;
}
-static bool __flush_work(struct work_struct *work)
-{
- struct wq_barrier barr;
-
- if (start_flush_work(work, &barr)) {
- wait_for_completion(&barr.done);
- destroy_work_on_stack(&barr.work);
- return true;
- } else {
- return false;
- }
-}
-
/**
* flush_work - wait for a work to finish executing the last queueing instance
* @work: the work to flush
@@ -2866,10 +2853,18 @@ static bool __flush_work(struct work_struct *work)
*/
bool flush_work(struct work_struct *work)
{
+ struct wq_barrier barr;
+
lock_map_acquire(&work->lockdep_map);
lock_map_release(&work->lockdep_map);
- return __flush_work(work);
+ if (start_flush_work(work, &barr)) {
+ wait_for_completion(&barr.done);
+ destroy_work_on_stack(&barr.work);
+ return true;
+ } else {
+ return false;
+ }
}
EXPORT_SYMBOL_GPL(flush_work);
@@ -4814,14 +4809,7 @@ long work_on_cpu(int cpu, long (*fn)(void *), void *arg)
INIT_WORK_ONSTACK(&wfc.work, work_for_cpu_fn);
schedule_work_on(cpu, &wfc.work);
-
- /*
- * The work item is on-stack and can't lead to deadlock through
- * flushing. Use __flush_work() to avoid spurious lockdep warnings
- * when work_on_cpu()s are nested.
- */
- __flush_work(&wfc.work);
-
+ flush_work(&wfc.work);
return wfc.ret;
}
EXPORT_SYMBOL_GPL(work_on_cpu);
--
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