commit 52cdbdd49853 ("driver core: correct device's shutdown order")
places an assumption of supplier<-consumer order on the process of probe.
But it turns out to break down the parent <- child order in some scene.
E.g in pci, a bridge is enabled by pci core, and behind it, the devices
have been probed. Then comes the bridge's module, which enables extra
feature(such as hotplug) on this bridge. This will break the
parent<-children order and cause failure when "kexec -e" in some scenario.
The detailed description of the scenario:
An IBM Power9 machine on which, two drivers portdrv_pci and shpchp(a mod)
match the PCI_CLASS_BRIDGE_PCI, but neither of them success to probe due
to some issue. For this case, the bridge is moved after its children in
devices_kset. Then, when "kexec -e", a ata-disk behind the bridge can not
write back buffer in flight due to the former shutdown of the bridge which
clears the BusMaster bit.
To fix this issue, only reordering a device and all of its children
if it is a consumer.
Note, the bridge involved:
0004:00:00.0 PCI bridge: IBM Device 04c1 (prog-if 00 [Normal decode])
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx-
Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 0
NUMA node: 0
Bus: primary=00, secondary=01, subordinate=12, sec-latency=0
I/O behind bridge: 00000000-00000fff
Memory behind bridge: 80000000-ffefffff
Prefetchable memory behind bridge: 0006024000000000-0006027f7fffffff
Secondary status: 66MHz- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- <SERR- <PERR-
BridgeCtl: Parity- SERR+ NoISA- VGA- MAbort- >Reset- FastB2B-
PriDiscTmr- SecDiscTmr- DiscTmrStat- DiscTmrSERREn-
Capabilities: [40] Power Management version 3
Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA PME(D0+,D1-,D2-,D3hot+,D3cold+)
Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
Capabilities: [48] Express (v2) Root Port (Slot-), MSI 00
DevCap: MaxPayload 512 bytes, PhantFunc 0
ExtTag- RBE+
DevCtl: Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop-
MaxPayload 256 bytes, MaxReadReq 128 bytes
DevSta: CorrErr- UncorrErr- FatalErr- UnsuppReq- AuxPwr- TransPend-
LnkCap: Port #0, Speed 8GT/s, Width x8, ASPM not supported, Exit Latency L0s <64ns, L1 <1us
ClockPM- Surprise- LLActRep+ BwNot+ ASPMOptComp-
LnkCtl: ASPM Disabled; RCB 128 bytes Disabled- CommClk-
ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
LnkSta: Speed 8GT/s, Width x4, TrErr- Train- SlotClk- DLActive+ BWMgmt- ABWMgmt+
RootCtl: ErrCorrectable- ErrNon-Fatal- ErrFatal- PMEIntEna- CRSVisible-
RootCap: CRSVisible-
RootSta: PME ReqID 0000, PMEStatus- PMEPending-
DevCap2: Completion Timeout: Range ABCD, TimeoutDis+, LTR-, OBFF Not Supported ARIFwd+
DevCtl2: Completion Timeout: 16ms to 55ms, TimeoutDis+, LTR-, OBFF Disabled ARIFwd+
LnkCtl2: Target Link Speed: 8GT/s, EnterCompliance- SpeedDis-
Transmit Margin: Normal Operating Range, EnterModifiedCompliance- ComplianceSOS-
Compliance De-emphasis: -6dB
LnkSta2: Current De-emphasis Level: -3.5dB, EqualizationComplete+, EqualizationPhase1+
EqualizationPhase2+, EqualizationPhase3+, LinkEqualizationRequest-
Capabilities: [100 v1] Advanced Error Reporting
UESta: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq- ACSViol-
UEMsk: DLP- SDES- TLP+ FCP- CmpltTO+ CmpltAbrt+ UnxCmplt- RxOF- MalfTLP- ECRC+ UnsupReq- ACSViol-
UESvrt: DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq- ACSViol-
CESta: RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr-
CEMsk: RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr-
AERCap: First Error Pointer: 00, GenCap+ CGenEn+ ChkCap+ ChkEn+
Capabilities: [148 v1] #19
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Cc: Dave Young <redacted>
Cc: linux-pci@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Pingfan Liu <redacted>
---
note: this patch points out the code where the bug is introduced.
and I hope it sketches out the scene. Will fold the series in one.
---
drivers/base/base.h | 1 +
drivers/base/core.c | 9 +++++++++
drivers/base/dd.c | 9 ++-------
3 files changed, 12 insertions(+), 7 deletions(-)
diff --git a/drivers/base/base.h b/drivers/base/base.h
index a75c302..37f86ca 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -135,6 +135,7 @@ extern void device_unblock_probing(void);
/* /sys/devices directory */
extern struct kset *devices_kset;
+extern int device_reorder_consumer(struct device *dev);
extern void devices_kset_move_last(struct device *dev);
#if defined(CONFIG_MODULES) && defined(CONFIG_SYSFS)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 36622b5..66f06ff 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -123,6 +123,15 @@ static int device_is_dependent(struct device *dev, void *target)
return ret;
}
+/* a temporary place holder to mark out the root cause of the bug.
+ * The proposal algorithm will come in next patch
+ */
+int device_reorder_consumer(struct device *dev)
+{
+ devices_kset_move_last(dev);
+ return 0;
+}
+
static int device_reorder_to_tail(struct device *dev, void *not_used)
{
struct device_link *link;diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 1435d72..c74f23c 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -434,13 +434,8 @@ static int really_probe(struct device *dev, struct device_driver *drv)
goto probe_failed;
}
- /*
- * Ensure devices are listed in devices_kset in correct order
- * It's important to move Dev to the end of devices_kset before
- * calling .probe, because it could be recursive and parent Dev
- * should always go first
- */
- devices_kset_move_last(dev);
+ /* only reoder consumer and its children after suppliers.*/
+ device_reorder_consumer(dev);
if (dev->bus->probe) {
ret = dev->bus->probe(dev);--
2.7.4
On Mon, Jun 25, 2018 at 03:47:39PM +0800, Pingfan Liu wrote:
commit 52cdbdd49853 ("driver core: correct device's shutdown order")
introduces supplier<-consumer order in devices_kset. The commit tries
to cleverly maintain both parent<-child and supplier<-consumer order by
reordering a device when probing. This method makes things simple and
clean, but unfortunately, breaks parent<-child order in some case,
which is described in next patch in this series.
There is no "next patch in this series" :(
Here this patch tries to resolve supplier<-consumer by only reordering a
device when it has suppliers, and takes care of the following scenario:
[consumer, children] [ ... potential ... ] supplier
^ ^
After moving the consumer and its children after the supplier, the
potentail section may contain consumers whose supplier is inside
children, and this poses the requirement to dry out all consumpers in
the section recursively.
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Cc: Dave Young <redacted>
Cc: linux-pci@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Pingfan Liu <redacted>
---
note: there is lock issue in this patch, should be fixed in next version
Please send patches that you know are correct, why would I want to
review this if you know it is not correct?
And if the original commit is causing problems for you, why not just
revert that instead of adding this much-increased complexity?
quoted hunk
---
drivers/base/core.c | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 129 insertions(+), 3 deletions(-)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 66f06ff..db30e86 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -123,12 +123,138 @@ static int device_is_dependent(struct device *dev, void *target)
return ret;
}
-/* a temporary place holder to mark out the root cause of the bug.
- * The proposal algorithm will come in next patch
+struct pos_info {
+ struct device *pos;
+ struct device *tail;
+};
+
+/* caller takes the devices_kset->list_lock */
+static int descendants_reorder_after_pos(struct device *dev,
+ void *data)
Why are you wrapping lines that do not need to be wrapped?
What does this function do?
+{
+ struct device *pos;
+ struct pos_info *p = data;
+
+ pos = p->pos;
+ pr_debug("devices_kset: Moving %s after %s\n",
+ dev_name(dev), dev_name(pos));
You have a device, use it for debugging, i.e. dev_dbg().
+ device_for_each_child(dev, p, descendants_reorder_after_pos);
Recursive?
+ /* children at the tail */
+ list_move(&dev->kobj.entry, &pos->kobj.entry);
+ /* record the right boundary of the section */
+ if (p->tail == NULL)
+ p->tail = dev;
+ return 0;
+}
I really do not understand what the above code is supposed to be doing :(
+
+/* iterate over an open section */
+#define list_opensect_for_each_reverse(cur, left, right) \
+ for (cur = right->prev; cur == left; cur = cur->prev)
+
+static bool is_consumer(struct device *query, struct device *supplier)
+{
+ struct device_link *link;
+ /* todo, lock protection */
Always run checkpatch.pl on patches so you do not get grumpy maintainers
telling you to run checkpatch.pl :(
+ list_for_each_entry(link, &supplier->links.consumers, s_node)
+ if (link->consumer == query)
+ return true;
+ return false;
+}
+
+/* recursively move the potential consumers in open section (left, right)
+ * after the barrier
What barrier?
I'm stopping here as I have no idea what is going on, and this needs a
lot more work at the basic level of "it handles locking correctly"...
If you are working on this for power9, I'm guessing you work for IBM?
If so, please run this through your internal patch review process before
sending it out again...
thanks,
greg k-h
On Mon, Jun 25, 2018 at 6:45 PM Greg Kroah-Hartman
[off-list ref] wrote:
On Mon, Jun 25, 2018 at 03:47:39PM +0800, Pingfan Liu wrote:
quoted
commit 52cdbdd49853 ("driver core: correct device's shutdown order")
introduces supplier<-consumer order in devices_kset. The commit tries
to cleverly maintain both parent<-child and supplier<-consumer order by
reordering a device when probing. This method makes things simple and
clean, but unfortunately, breaks parent<-child order in some case,
which is described in next patch in this series.
There is no "next patch in this series" :(
Oh, re-arrange the patches, and forget the comment in log
quoted
Here this patch tries to resolve supplier<-consumer by only reordering a
device when it has suppliers, and takes care of the following scenario:
[consumer, children] [ ... potential ... ] supplier
^ ^
After moving the consumer and its children after the supplier, the
potentail section may contain consumers whose supplier is inside
children, and this poses the requirement to dry out all consumpers in
the section recursively.
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Cc: Dave Young <redacted>
Cc: linux-pci@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Pingfan Liu <redacted>
---
note: there is lock issue in this patch, should be fixed in next version
Please send patches that you know are correct, why would I want to
review this if you know it is not correct?
And if the original commit is causing problems for you, why not just
revert that instead of adding this much-increased complexity?
Revert the original commit, then it will expose the error order
"consumer <- supplier" again.
This patch tries to resolve the error and fix the following scenario:
step0: before the consumer device's probing, (note child_a is a
supplier of consumer_a, etc)
[ consumer-X, child_a, ...., child_z] [.... consumer_a, ...,
consumer_z, ....] supplier-X
^^^
affected range during moving^^^
step1: When probing, moving consumer-X after supplier-X
[ child_a, ...., child_z] [.... consumer_a, ..., consumer_z,
....] supplier-X, consumer-X
But it breaks "parent <-child" seq now, and should be fixed like:
step2:
[.... consumer_a, ..., consumer_z, ....] supplier-X [
consumer-X, child_a, ...., child_z] <---
descendants_reorder_after_pos() does it.
Again, the seq "consumer_a <- child_a" breaks the "supplier<-consumer"
order, should be fixed like:
step3:
[.... consumer_z, .....] supplier-X [ consumer-X, child_a,
consumer_a ...., child_z] <--- __device_reorder_consumer() does it.
^^ affected range^^
The moving of consumer_a brings us to face the same scenario of step1,
hence we need an external recursion.
Each round of step3, __device_reorder_consumer() resolves its "local
affected range", which is a fraction of the "whole affected range".
Hence finally, we have all potential consumers in affected range resolved.
(Maybe I can split patch at step2 and step3 to ease the review for the
next version)
Since __device_reorder_consumer() has already hold devices_kset's spin
lock, and need to get srcu lock on devices->links.consumers.
This needs a breakage of spin lock, and will incur much effort. If the
above algorithm is fine, I can do it.
quoted
---
drivers/base/core.c | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 129 insertions(+), 3 deletions(-)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 66f06ff..db30e86 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -123,12 +123,138 @@ static int device_is_dependent(struct device *dev, void *target)
return ret;
}
-/* a temporary place holder to mark out the root cause of the bug.
- * The proposal algorithm will come in next patch
+struct pos_info {
+ struct device *pos;
+ struct device *tail;
+};
+
+/* caller takes the devices_kset->list_lock */
+static int descendants_reorder_after_pos(struct device *dev,
+ void *data)
Why are you wrapping lines that do not need to be wrapped?
OK, will fix.
What does this function do?
As the name implies, reordering dev and its children after a position.
When moving a consumer after a supplier, we break down the order
of "parent <-child" order of consumer and its children in devices_kset.
Hence we should move the children too.
The param "data" contains the position info, and its name is not
illuminated :(,
since the func proto is required by device_for_each_child(), may be better to
name it as postion_info
quoted
+{
+ struct device *pos;
+ struct pos_info *p = data;
+
+ pos = p->pos;
+ pr_debug("devices_kset: Moving %s after %s\n",
+ dev_name(dev), dev_name(pos));
You have a device, use it for debugging, i.e. dev_dbg().
But here we have two devices.
quoted
+ device_for_each_child(dev, p, descendants_reorder_after_pos);
Recursive?
Yes, in order to move all children of the consumer.
quoted
+ /* children at the tail */
+ list_move(&dev->kobj.entry, &pos->kobj.entry);
+ /* record the right boundary of the section */
+ if (p->tail == NULL)
+ p->tail = dev;
+ return 0;
+}
I really do not understand what the above code is supposed to be doing :(
The moved consumer's children may be suppliers of devices,
[.... consumer_a, ..., consumer_z, ....] supplier-X [
consumer-X, child_a, ............, child_z]
^^^ potential consumers ^^^^^^
^^potential suppliers^^
Now, consumer_a and its supplier child_a violate the order
"supplier<-consumer".
To pick out such violation, we need to check the potential suppliers
against potential
consumers. And p->tail helps to record the new moved position of child_z.
quoted
+
+/* iterate over an open section */
+#define list_opensect_for_each_reverse(cur, left, right) \
+ for (cur = right->prev; cur == left; cur = cur->prev)
+
+static bool is_consumer(struct device *query, struct device *supplier)
+{
+ struct device_link *link;
+ /* todo, lock protection */
Always run checkpatch.pl on patches so you do not get grumpy maintainers
telling you to run checkpatch.pl :(
Yes, I had run it, and only got a warning:
WARNING: Avoid crashing the kernel - try using WARN_ON & recovery code
rather than BUG() or BUG_ON()
#167: FILE: drivers/base/core.c:245:
+ BUG_ON(!ret);
total: 0 errors, 1 warnings, 141 lines checked
quoted
+ list_for_each_entry(link, &supplier->links.consumers, s_node)
+ if (link->consumer == query)
+ return true;
+ return false;
+}
+
+/* recursively move the potential consumers in open section (left, right)
+ * after the barrier
What barrier?
A position that moved devices can not cross before.
I'm stopping here as I have no idea what is going on, and this needs a
lot more work at the basic level of "it handles locking correctly"...
If you are working on this for power9, I'm guessing you work for IBM?
No. I just hit this bug.
If so, please run this through your internal patch review process before
sending it out again...
I will try my best to find some guys to review. But is the assumption
of step0 and
the following algorithm worth to try?
Thanks and regards,
Pingfan
On Tue, Jun 26, 2018 at 11:29:48AM +0800, Pingfan Liu wrote:
On Mon, Jun 25, 2018 at 6:45 PM Greg Kroah-Hartman
[off-list ref] wrote:
quoted
On Mon, Jun 25, 2018 at 03:47:39PM +0800, Pingfan Liu wrote:
quoted
commit 52cdbdd49853 ("driver core: correct device's shutdown order")
introduces supplier<-consumer order in devices_kset. The commit tries
to cleverly maintain both parent<-child and supplier<-consumer order by
reordering a device when probing. This method makes things simple and
clean, but unfortunately, breaks parent<-child order in some case,
which is described in next patch in this series.
There is no "next patch in this series" :(
Oh, re-arrange the patches, and forget the comment in log
quoted
quoted
Here this patch tries to resolve supplier<-consumer by only reordering a
device when it has suppliers, and takes care of the following scenario:
[consumer, children] [ ... potential ... ] supplier
^ ^
After moving the consumer and its children after the supplier, the
potentail section may contain consumers whose supplier is inside
children, and this poses the requirement to dry out all consumpers in
the section recursively.
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Cc: Dave Young <redacted>
Cc: linux-pci@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Pingfan Liu <redacted>
---
note: there is lock issue in this patch, should be fixed in next version
Please send patches that you know are correct, why would I want to
review this if you know it is not correct?
And if the original commit is causing problems for you, why not just
revert that instead of adding this much-increased complexity?
Revert the original commit, then it will expose the error order
"consumer <- supplier" again.
This patch tries to resolve the error and fix the following scenario:
step0: before the consumer device's probing, (note child_a is a
supplier of consumer_a, etc)
[ consumer-X, child_a, ...., child_z] [.... consumer_a, ...,
consumer_z, ....] supplier-X
^^^
affected range during moving^^^
step1: When probing, moving consumer-X after supplier-X
[ child_a, ...., child_z] [.... consumer_a, ..., consumer_z,
....] supplier-X, consumer-X
But it breaks "parent <-child" seq now, and should be fixed like:
step2:
[.... consumer_a, ..., consumer_z, ....] supplier-X [
consumer-X, child_a, ...., child_z] <---
descendants_reorder_after_pos() does it.
Again, the seq "consumer_a <- child_a" breaks the "supplier<-consumer"
order, should be fixed like:
step3:
[.... consumer_z, .....] supplier-X [ consumer-X, child_a,
consumer_a ...., child_z] <--- __device_reorder_consumer() does it.
^^ affected range^^
The moving of consumer_a brings us to face the same scenario of step1,
hence we need an external recursion.
Something really got messed up here, and this all does not make any
sense :(
Can you try again?
Also, please cc: Rafael on all of this, as he wrote all of this
consumer/supplier logic and I am not that familiar with it at all.
thanks,
greg k-h