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Message-ID: <20200204154236.GE14879@hirez.programming.kicks-ass.net>
Date: Tue, 4 Feb 2020 16:42:36 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Waiman Long <longman@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
linux-kernel@...r.kernel.org, Bart Van Assche <bvanassche@....org>
Subject: Re: [PATCH v5 6/7] locking/lockdep: Reuse freed chain_hlocks entries
On Mon, Feb 03, 2020 at 11:41:46AM -0500, Waiman Long wrote:
> + /*
> + * We require a minimum of 2 (u16) entries to encode a freelist
> + * 'pointer'.
> + */
> + req = max(req, 2);
Would something simple like the below not avoid that whole 1 entry
'chain' nonsense?
It boots and passes the selftests, so it must be perfect :-)
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3163,7 +3163,7 @@ static int validate_chain(struct task_st
* (If lookup_chain_cache_add() return with 1 it acquires
* graph_lock for us)
*/
- if (!hlock->trylock && hlock->check &&
+ if (!chain_head && !hlock->trylock && hlock->check &&
lookup_chain_cache_add(curr, hlock, chain_key)) {
/*
* Check whether last held lock:
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