linux-kernel - Re: [RFC 00/12] locking: Separate lock tracepoints from lockdep/lock

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Message-ID: <f8b7760f-16a2-6ada-de88-9e21a7e8fef9@redhat.com>
Date:   Wed, 9 Feb 2022 15:17:38 -0500
From:   Waiman Long <longman@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        rostedt <rostedt@...dmis.org>,
        Byungchul Park <byungchul.park@....com>,
        Radoslaw Burny <rburny@...gle.com>, Tejun Heo <tj@...nel.org>,
        rcu <rcu@...r.kernel.org>, cgroups <cgroups@...r.kernel.org>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        paulmck <paulmck@...nel.org>
Subject: Re: [RFC 00/12] locking: Separate lock tracepoints from
 lockdep/lock_stat (v1)


On 2/9/22 14:45, Namhyung Kim wrote:
> On Wed, Feb 9, 2022 at 11:28 AM Mathieu Desnoyers
> <mathieu.desnoyers@...icios.com> wrote:
>> ----- On Feb 9, 2022, at 2:22 PM, Namhyung Kim namhyung@...nel.org wrote:
>>> I'm also concerning dynamic allocated locks in a data structure.
>>> If we keep the info in a hash table, we should delete it when the
>>> lock is gone.  I'm not sure we have a good place to hook it up all.
>> I was wondering about this use case as well. Can we make it mandatory to
>> declare the lock "class" (including the name) statically, even though the
>> lock per-se is allocated dynamically ? Then the initialization of the lock
>> embedded within the data structure would simply refer to the lock class
>> definition.
> Isn't it still the same if we have static lock classes that the entry needs
> to be deleted from the hash table when it frees the data structure?
> I'm more concerned about free than alloc as there seems to be no
> API to track that in a place.

We may have to invent some new APIs to do that. For example, 
spin_lock_exit() can be the counterpart of spin_lock_init() and so on. 
Of course, existing kernel code have to be modified to designate the 
point after which a lock is no longer being used or is freed.

Cheers,
Longman