* [PATCH] docs: kref: Clarify the use of two kref_put() in example code
@ 2020-02-13 12:53 Manivannan Sadhasivam
2020-02-19 10:58 ` Jonathan Corbet
0 siblings, 1 reply; 4+ messages in thread
From: Manivannan Sadhasivam @ 2020-02-13 12:53 UTC (permalink / raw)
To: corbet; +Cc: linux-doc, linux-kernel, Manivannan Sadhasivam
Eventhough the current documentation explains that the reference count
gets incremented by both kref_init() and kref_get(), it is often
misunderstood that only one instance of kref_put() is needed in the
example code. So let's clarify that a bit.
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
Documentation/kref.txt | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/Documentation/kref.txt b/Documentation/kref.txt
index 3af384156d7e..c61eea6f1bf2 100644
--- a/Documentation/kref.txt
+++ b/Documentation/kref.txt
@@ -128,6 +128,10 @@ since we already have a valid pointer that we own a refcount for. The
put needs no lock because nothing tries to get the data without
already holding a pointer.
+In the above example, kref_put() will be called 2 times in both success
+and error paths. This is necessary because the reference count got
+incremented 2 times by kref_init() and kref_get().
+
Note that the "before" in rule 1 is very important. You should never
do something like::
--
2.17.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] docs: kref: Clarify the use of two kref_put() in example code
2020-02-13 12:53 [PATCH] docs: kref: Clarify the use of two kref_put() in example code Manivannan Sadhasivam
@ 2020-02-19 10:58 ` Jonathan Corbet
2020-02-19 11:10 ` Manivannan Sadhasivam
0 siblings, 1 reply; 4+ messages in thread
From: Jonathan Corbet @ 2020-02-19 10:58 UTC (permalink / raw)
To: Manivannan Sadhasivam; +Cc: linux-doc, linux-kernel
On Thu, 13 Feb 2020 18:23:11 +0530
Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> wrote:
> Eventhough the current documentation explains that the reference count
> gets incremented by both kref_init() and kref_get(), it is often
> misunderstood that only one instance of kref_put() is needed in the
> example code. So let's clarify that a bit.
>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
> Documentation/kref.txt | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/Documentation/kref.txt b/Documentation/kref.txt
> index 3af384156d7e..c61eea6f1bf2 100644
> --- a/Documentation/kref.txt
> +++ b/Documentation/kref.txt
> @@ -128,6 +128,10 @@ since we already have a valid pointer that we own a refcount for. The
> put needs no lock because nothing tries to get the data without
> already holding a pointer.
>
> +In the above example, kref_put() will be called 2 times in both success
> +and error paths. This is necessary because the reference count got
> +incremented 2 times by kref_init() and kref_get().
Out of curiosity, where have you seen this misunderstanding happening?
I'm not really opposed to this change, but I don't understand why it's
really needed.
Thanks,
jon
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] docs: kref: Clarify the use of two kref_put() in example code
2020-02-19 10:58 ` Jonathan Corbet
@ 2020-02-19 11:10 ` Manivannan Sadhasivam
2020-02-25 10:39 ` Jonathan Corbet
0 siblings, 1 reply; 4+ messages in thread
From: Manivannan Sadhasivam @ 2020-02-19 11:10 UTC (permalink / raw)
To: Jonathan Corbet; +Cc: linux-doc, linux-kernel
Hi Jon,
On Wed, Feb 19, 2020 at 03:58:18AM -0700, Jonathan Corbet wrote:
> On Thu, 13 Feb 2020 18:23:11 +0530
> Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> wrote:
>
> > Eventhough the current documentation explains that the reference count
> > gets incremented by both kref_init() and kref_get(), it is often
> > misunderstood that only one instance of kref_put() is needed in the
> > example code. So let's clarify that a bit.
> >
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > ---
> > Documentation/kref.txt | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/Documentation/kref.txt b/Documentation/kref.txt
> > index 3af384156d7e..c61eea6f1bf2 100644
> > --- a/Documentation/kref.txt
> > +++ b/Documentation/kref.txt
> > @@ -128,6 +128,10 @@ since we already have a valid pointer that we own a refcount for. The
> > put needs no lock because nothing tries to get the data without
> > already holding a pointer.
> >
> > +In the above example, kref_put() will be called 2 times in both success
> > +and error paths. This is necessary because the reference count got
> > +incremented 2 times by kref_init() and kref_get().
>
> Out of curiosity, where have you seen this misunderstanding happening?
> I'm not really opposed to this change, but I don't understand why it's
> really needed.
>
Jakub mistakenly spotted one refcounting issue in one of my patchset:
https://lkml.org/lkml/2020/2/3/926
Then I tried to show him the kernel doc for kref and that's where I got this
example code slightly confusing. And while looking into the log, I noticed that
someone deleted the kref_put in error path mistakenly and that commit got
reverted after that. This issue was even discussed in stack overflow.
http://stackoverflow.com/questions/20093127/why-kref-doc-of-linux-kernel-omits-kref-put-when-kthread-run-fail
So I thought about making it more clear of why the kref_put is needed in error
path.
Thanks,
Mani
> Thanks,
>
> jon
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] docs: kref: Clarify the use of two kref_put() in example code
2020-02-19 11:10 ` Manivannan Sadhasivam
@ 2020-02-25 10:39 ` Jonathan Corbet
0 siblings, 0 replies; 4+ messages in thread
From: Jonathan Corbet @ 2020-02-25 10:39 UTC (permalink / raw)
To: Manivannan Sadhasivam; +Cc: linux-doc, linux-kernel
On Wed, 19 Feb 2020 16:40:55 +0530
Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> wrote:
> Jakub mistakenly spotted one refcounting issue in one of my patchset:
> https://lkml.org/lkml/2020/2/3/926
>
> Then I tried to show him the kernel doc for kref and that's where I got this
> example code slightly confusing. And while looking into the log, I noticed that
> someone deleted the kref_put in error path mistakenly and that commit got
> reverted after that. This issue was even discussed in stack overflow.
>
> http://stackoverflow.com/questions/20093127/why-kref-doc-of-linux-kernel-omits-kref-put-when-kthread-run-fail
>
> So I thought about making it more clear of why the kref_put is needed in error
> path.
OK, I've applied it, thanks.
jon
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-02-13 12:53 [PATCH] docs: kref: Clarify the use of two kref_put() in example code Manivannan Sadhasivam
2020-02-19 10:58 ` Jonathan Corbet
2020-02-19 11:10 ` Manivannan Sadhasivam
2020-02-25 10:39 ` Jonathan Corbet
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