linux-kernel - Re: [PATCH] libnvdimm: Clarify nd_pfn

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Date:   Tue, 22 Jan 2019 08:23:35 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Wei Yang <richard.weiyang@...il.com>,
        Wei Yang <richardw.yang@...ux.intel.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libnvdimm: Clarify nd_pfn_init() flow

On Mon, Jan 21, 2019 at 02:34:06PM -0800, Dan Williams wrote:
>On Mon, Jan 21, 2019 at 12:57 PM Wei Yang <richard.weiyang@...il.com> wrote:
>>
>> On Mon, Jan 21, 2019 at 10:04:40AM -0800, Dan Williams wrote:
>> >On Sun, Jan 20, 2019 at 11:51 PM Wei Yang <richardw.yang@...ux.intel.com> wrote:
>> >> On Fri, Jan 18, 2019 at 04:47:23PM -0800, Dan Williams wrote:
>> >[..]
>> >> 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;
>> >
>> >Here is an example path for a device-dax instance:
>> >
>> >    /sys/devices/platform/e820_pmem/ndbus0/region0/dax0.1/dax0.0
>> >
>> >In this case the order of events is:
>> >
>> >1/ region0 discovers it contains a pmem namespace and registers namespace0.0
>> >2/ The pmem namespace driver calls nd_dax_probe() to check for the
>> >presence of a device-dax configuration
>> >3/ If present, nd_pfn_validate() returns 0 and nd_dax_probe()
>> >registers the dax0.1 device (this is a libnvdimm 'personality device).
>> >4/ When nd_pmem_probe() sees nd_dax_probe() return 0 it in turn fails
>> >the probe of namespace0.0 with -ENXIO. All devm allocations during the
>> >probe of namespace0.0 are released.
>>
>> I may have another opinion here.
>>
>> The probe return error means the device will not attach to this driver.
>> But the device itself it not released.
>>
>> We allocate devm on one device and those memory will be released when
>> the device is destroyed. If I am correct.
>>
>> This means at this point, pfn_sb's memory still exists in the system.
>> Even finally we will release it, when namespace0.0 is destroyed.
>
>No, that's not the way devm works. Memory allocated by devm is
>released at ->probe() failure, or after ->remove()
>
>See the devres_release_all() call in drivers/base/dd.c::really_probe()

Ah, you are right.

-- 
Wei Yang
Help you, Help me