linux-kernel - Re: [PATCH] ASoC: rt5682: Use a maple tree based register cache

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Date:   Tue, 23 May 2023 20:41:29 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     Oder Chiou <oder_chiou@...ltek.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ASoC: rt5682: Use a maple tree based register cache

On Tue, May 23, 2023 at 02:24:53PM -0500, Pierre-Louis Bossart wrote:

> I don't see any other changes to this codec driver and the first problem
> detected seemed to happen when we did an upstream merge last week.
> Unfortunately the last merge was on April 24 (sof-dev-rebase-20230424)
> which is just the day before this commit was added...

Try this:

From 5953e9de359674ff2d95fe4c241bc7880d6d0d82 Mon Sep 17 00:00:00 2001
From: Mark Brown <broonie@...nel.org>
Date: Tue, 23 May 2023 20:40:22 +0100
Subject: [PATCH] regmap: maple: Drop the RCU read lock while syncing registers

Unfortunately the maple tree requires us to explicitly lock it so we need
to take the RCU read lock while iterating. When syncing this means that we
end up trying to write out register values while holding the RCU read lock
which triggers lockdep issues since that is an atomic context but most
buses can't be used in atomic context. Pause the iteration and drop the
lock for each register we check to avoid this.

Reported-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 drivers/base/regmap/regcache-maple.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/base/regmap/regcache-maple.c b/drivers/base/regmap/regcache-maple.c
index 2d2d5d7ee447..14f6f49af097 100644
--- a/drivers/base/regmap/regcache-maple.c
+++ b/drivers/base/regmap/regcache-maple.c
@@ -203,15 +203,18 @@ static int regcache_maple_sync(struct regmap *map, unsigned int min,
 
 	mas_for_each(&mas, entry, max) {
 		for (r = max(mas.index, lmin); r <= min(mas.last, lmax); r++) {
+			mas_pause(&mas);
+			rcu_read_unlock();
 			ret = regcache_sync_val(map, r, entry[r - mas.index]);
 			if (ret != 0)
 				goto out;
+			rcu_read_lock();
 		}
 	}
 
-out:
 	rcu_read_unlock();
 
+out:
 	map->cache_bypass = false;
 
 	return ret;
-- 
2.30.2


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