linux-kernel - Re: [PATCH] lockdep: Show address of "struct lockdep_map" at print

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Message-ID: <20180326131911.GI5652@dhcp22.suse.cz>
Date:   Mon, 26 Mar 2018 15:19:11 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Borislav Petkov <bp@...e.de>,
        David Rientjes <rientjes@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] lockdep: Show address of "struct lockdep_map" at
 print_lock().

On Mon 26-03-18 19:18:33, Tetsuo Handa wrote:
> Currently, print_lock() is printing hlock->acquire_ip field in both
> "[<%px>]" and "%pS" format. But "[<%px>]" is little useful nowadays, for
> we use scripts/faddr2line which receives "%pS" for finding the location
> in the source code.
> 
> Since "struct lockdep_map" is embedded into lock objects, we can know
> which instance of a lock object is acquired using hlock->instance field.
> This will help finding which threads are causing a lock contention when
> e.g. the OOM reaper failed to acquire an OOM victim's mmap_sem for read.

How? All I can see is that we can match which instances are the same.
This would be an interesting thing to know AFAICS because you can tell
different instances of lock apart. So the patch makes some sense to me,
I am just not sure about changelog.
-- 
Michal Hocko
SUSE Labs