linux-kernel - RE: [PATCH 14/15] kernel: convert futex_pi_state.refcount from atomic_t to refcount

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Date:   Mon, 17 Jul 2017 16:51:22 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-audit@...hat.com" <linux-audit@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "tj@...nel.org" <tj@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "lizefan@...wei.com" <lizefan@...wei.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
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        "luto@...nel.org" <luto@...nel.org>,
        "keescook@...omium.org" <keescook@...omium.org>
Subject: RE: [PATCH 14/15] kernel: convert futex_pi_state.refcount from
 atomic_t to refcount_t

> On Mon, 17 Jul 2017, Elena Reshetova wrote:
> 
> > Subject: kernel: convert futex_pi_state.refcount from atomic_t to refcount_t
> 
> Several people including myself told you already, that subjects consist of
> 
> SUBSYSTEMPREFIX: Concise description
> 
> It's easy enough to figure the prefix out by looking at the output of 'git
> log path/of/changed/file'.

Ok, I will try this from now on. I didn't think of it, but was trying to figure it
based on general location and meaning (obviously wrong).

> 
> Concise descriptions are not lengthy sentences with implementation
> details. They should merily describe the problem/concept of change. The
> details go into the changelog. IOW, something like:
> 
> 	"PROPERPREFIX: Convert to refcount API"
> 
> would be sufficient.

OK, will fix. 

> 
> > refcount_t type and corresponding API should be
> > used instead of atomic_t when the variable is used as
> > a reference counter. This allows to avoid accidental
> > refcounter overflows that might lead to use-after-free
> > situations.
> 
> Copying the same sentence over and over avoids thinking about a proper
> changelog, right? You fail to explain, how you come to the conclusion that
> futex_pi_state.refcount is a pure reference counter (aside of the name) and
> therefor can be safely converted to refcount_t.

OK, this is not very useful for many cases. Yes, I am using automated log on
these patches, because I used to have 240 of them and writing manual logs for them
would be fun. Moreover, in many cases, writing manual logs don't bring any value since
I would have to repeat the same things all over again: xyz conversions was found by using *.cocci
pattern first, then looked at manually and it looked like a standard reference counter that
frees the things after calling refcount_dec_and_test() (or its variation with lock which is rare).
Other things also looked correct, like I didn't see increments from zero, counter starts at 1 etc.
I would really have to repeat the same thing in each changelog. Does it really bring value?

Best Regards,
Elena.
> 
> Other than that, the patch itself is fine.
> 
> Thanks,
> 
> 	tglx