linux-kernel - Re: [PATCH 3/4] locking/lockdep: Reduce space occupied by stack traces

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Message-ID: <ee1cd751-cc8a-ca03-e30c-34b4cf8a13bf@acm.org>
Date:   Wed, 24 Jul 2019 08:47:00 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Yuyang Du <duyuyang@...il.com>,
        Waiman Long <longman@...hat.com>
Subject: Re: [PATCH 3/4] locking/lockdep: Reduce space occupied by stack
 traces

On 7/23/19 9:56 PM, Eric Biggers wrote:
> Does this also fix any of the other bugs listed at
> https://lore.kernel.org/lkml/20190710055838.GC2152@sol.localdomain/
> ?
> 
> BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> BUG: MAX_LOCKDEP_CHAINS too low!
> BUG: MAX_LOCK_DEPTH too low! (2)
> BUG: MAX_LOCKDEP_ENTRIES too low!

Hi Eric,

I don't think so. This patch only affects the space occupied by stack 
traces and not the space occupied by any of the other lockdep data 
strutures. BTW, in that report I found the following:

Title:              BUG: MAX_LOCKDEP_CHAINS too low!
Last occurred:      5 days ago
Reported:           284 days ago

Title:              BUG: MAX_LOCK_DEPTH too low! (2)
Last occurred:      362 days ago
Reported:           392 days ago

Since these bugs were reported more than 150 days ago these bugs are 
older than my lockdep changes and hence not a regression due to my 
lockdep changes.

My patch series did not increase the number of "list_entries" tracked by 
lockdep so I don't think that the "BUG: MAX_LOCKDEP_ENTRIES too low" 
behavior can be triggered more easily due to my lockdep changes.

The "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!" complaint however may be 
related. I will check whether it is possible to reduce the space 
occupied by held lock chains again to what was needed before my patch 
series.

Bart.