Messages in this thread | | | Date | Mon, 21 Jan 2019 15:51:02 +0800 | From | Wei Yang <> | Subject | Re: [PATCH] libnvdimm: Clarify nd_pfn_init() flow |
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On Fri, Jan 18, 2019 at 04:47:23PM -0800, Dan Williams wrote: >In recent days, 2 engineers, including the original author of >nd_pfn_init(), overlooked the internal call to nd_pfn_validate() and the >implications to memory allocation. > >Clarify this situation to help anyone that reads through this code in >the future. > >Reported-by: Wei Yang <richardw.yang@linux.intel.com> >Signed-off-by: Dan Williams <dan.j.williams@intel.com> >--- > drivers/nvdimm/btt_devs.c | 5 +++++ > drivers/nvdimm/dax_devs.c | 5 +++++ > drivers/nvdimm/pfn_devs.c | 21 +++++++++++++++++++++ > 3 files changed, 31 insertions(+) > >diff --git a/drivers/nvdimm/btt_devs.c b/drivers/nvdimm/btt_devs.c >index 795ad4ff35ca..e0a6f2491e57 100644 >--- a/drivers/nvdimm/btt_devs.c >+++ b/drivers/nvdimm/btt_devs.c >@@ -354,6 +354,11 @@ int nd_btt_probe(struct device *dev, struct nd_namespace_common *ndns) > put_device(btt_dev); > } > >+ /* >+ * Successful probe indicates to the caller that an nd_btt >+ * personality device has been registered and the caller can >+ * fail the probe of the baseline namespace device. >+ */ > return rc; > } > EXPORT_SYMBOL(nd_btt_probe); >diff --git a/drivers/nvdimm/dax_devs.c b/drivers/nvdimm/dax_devs.c >index 0453f49dc708..65010d955fa7 100644 >--- a/drivers/nvdimm/dax_devs.c >+++ b/drivers/nvdimm/dax_devs.c >@@ -136,6 +136,11 @@ int nd_dax_probe(struct device *dev, struct nd_namespace_common *ndns) > } else > __nd_device_register(dax_dev); > >+ /* >+ * Successful probe indicates to the caller that a device-dax >+ * personality device has been registered and the caller can >+ * fail the probe of the baseline namespace device. >+ */ > return rc; > } > EXPORT_SYMBOL(nd_dax_probe); >diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c >index 6f22272e8d80..a8783b5a76ba 100644 >--- a/drivers/nvdimm/pfn_devs.c >+++ b/drivers/nvdimm/pfn_devs.c >@@ -576,6 +576,11 @@ int nd_pfn_probe(struct device *dev, struct nd_namespace_common *ndns) > } else > __nd_device_register(pfn_dev); > >+ /* >+ * Successful probe indicates to the caller that an nd_pfn >+ * personality device has been registered and the caller can >+ * fail the probe of the baseline namespace device. >+ */ > return rc; > } > EXPORT_SYMBOL(nd_pfn_probe); >@@ -706,6 +711,22 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn) > sig = DAX_SIG; > else > sig = PFN_SIG; >+ >+ /* >+ * Check for an existing 'pfn' superblock before writing a new >+ * one. The intended flow is that on the first probe of an >+ * nd_{pfn,dax} device the superblock is calculated and written >+ * to the namespace. In this case nd_pfn_validate() returns >+ * -ENODEV because no valid superblock exists currently. >+ * >+ * On subsequent probes nd_pfn_validate() will find a valid >+ * superblock and return 0. >+ * >+ * If an assumption of the superblock has been violated, like a >+ * change to the physical alignment of the namespace, >+ * nd_pfn_validate() will return an error other than -ENODEV to >+ * fail probing. >+ */
Let me reply in this thread. Sorry for my poor understand, I don't get it clearly now.
To be honest, the structure is a little bit complicated, if my understanding is not correct, please forgive my poor understand.
Below is a code flow. To simply analysis, I setup kernel parameter memmap to emulate, and configure one namespace to mode devdax. So that we would have the same root for code flow.
Let's start with nd_region_driver:
nd_region_probe nd_region_register_namespaces create_namespaces nd_region->btt_seed = nd_btt_create(nd_region); nd_region->pfn_seed = nd_pfn_create(nd_region); nd_region->dax_seed = nd_dax_create(nd_region);
After this, there are 4 devices created:
namespace0.0, btt0.0, pfn0.0, dax0.0
And there are two drivers related to these devices. The relationship between devices and drivers are:
nd_pmem_driver: namespace0.0, btt0.0, pfn0.0 dax_pmem_driver: dax0.0
Only the probe function on namespace0.0 succeed. Even others get -ENODEV, those devices themself is not released.
Then let's look at the probe on namespace0.0:
nd_pmem_probe nd_btt_probe nd_pfn_probe nd_dax_probe
When namespace is configured as devdax, only nd_dax_probe do some real work.
Then I see some different behavior as your description.
* nd_dax_probe->nd_pfn_validate() return 0 instead of -ENODEV. * so device dax0.1 is created * dax_pmem_probe is called on dax0.1 and nd_pfn_validate() return 0 too
This means pfn_sb is created twice in following functions:
* nd_dax_probe * dax_pmem_probe
Also, I have one confusion about your saying: two probes.
If the two probes are:
* for dax%d.%d: 1. nd_dax_probe 2. dax_pmem_probe * for pfn%d.%d: 1. nd_pfn_probe 2. nd_pmem_probe
Then, if the first probe fails, the device itself would be destroyed. How the second probe do its job?
> rc = nd_pfn_validate(nd_pfn, sig); > if (rc != -ENODEV) > return rc;
-- Wei Yang Help you, Help me
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