From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D779327B4F7; Sun, 19 Apr 2026 16:10:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776615012; cv=none; b=F6ySKGFv7hXpoTVs+ORS2FEaxqsBvV1IJfKJC1QbMRUEOaahfoX1dCAwd0smhwaGBKGuNgD3sTkEpScSJnoeAZwsUGQ2NCCq26Ph0AhTtYJXiqPtZs46MeKypFRvKK9GQHn8Hl9RnvlF0EBDOqmpcFWPuihq0RiFYbCAxR2f/Fo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776615012; c=relaxed/simple; bh=rIOaDq/KHXQ6SzD1AFFL4LR91YKZhChannZeLdJ236k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mWQoDR12VEDacLUivlLQ5wZj0dPCXU28tnGf2ZZqct8OegENC7QwSS1L2IN0Pse9ZOj8XrjzGQADWIB+zBwiN/7J3XD+/nBMjrEoxaW04ajLVYYmjCiiRYuAVYkYcYgrqK+1MnRjyH9s1UoER8l2Xr3Z3N4ZqzOMHLaanAUXta8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=V/F6L+rD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="V/F6L+rD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 77892C2BCAF; Sun, 19 Apr 2026 16:10:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776615012; bh=rIOaDq/KHXQ6SzD1AFFL4LR91YKZhChannZeLdJ236k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=V/F6L+rDzvl2gUnTte2b1pXCBREgpl8MSm54iG5JOxUR3qhDYp4bkHkWohjIP26Bj gSXNwAalq2hNRlHvoczkAPcqlnAag25yct3Iw6HNGwmO+DCvugOlhNHBJXNyG7mznt EkOEYKjikzKIa8pruVhZ83xlrwezSNFEX6QBMqA58EwheInlFegTK67SZ4hlu1EV6e XlAu5Wy8FR/PfGfp/1FCgtlcuqWuB8UegsnP/htRYLRNg6qu2iurV9pjqyzHBxQ13u gicTsL+a6Eda6RLU2Xe770O28vHYBEj+nDDTt9GiLHXvjfNrM9AX6E1JRy8HXqzYZ1 ZfLPTuCFXFPlQ== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , "# 6 . 17 . x" , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 3/3] mm/damon/stat: detect and use fresh enabled value Date: Sun, 19 Apr 2026 09:10:02 -0700 Message-ID: <20260419161003.79176-4-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260419161003.79176-1-sj@kernel.org> References: <20260419161003.79176-1-sj@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit DAMON_STAT updates 'enabled' parameter value, which represents the running status of its kdamond, when the user explicitly requests start/stop of the kdamond. The kdamond can, however, be stopped even if the user explicitly requested the stop, if ctx->regions_score_histogram allocation failure at beginning of the execution of the kdamond. Hence, if the kdamond is stopped by the allocation failure, the value of the parameter can be stale. Users could show the stale value and be confused. The problem will only rarely happen in real and common setups because the allocation is arguably too small to fail. Also, unlike the similar bugs that are now fixed in DAMON_RECLAIM and DAMON_LRU_SORT, kdamond can be restarted in this case, because DAMON_STAT force-updates the enabled parameter value for user inputs. The bug is a bug, though. The issue stems from the fact that there are multiple events that can change the status, and following all the events is challenging. Dynamically detect and use the fresh status for the parameters when those are requested. The issue was dicovered [1] by Sashiko. [1] https://lore.kernel.org/20260416040602.88665-1-sj@kernel.org Fixes: 369c415e6073 ("mm/damon: introduce DAMON_STAT module") Cc: # 6.17.x Signed-off-by: SeongJae Park --- mm/damon/stat.c | 30 ++++++++++++++++++++---------- 1 file changed, 20 insertions(+), 10 deletions(-) diff --git a/mm/damon/stat.c b/mm/damon/stat.c index 99ba346f9e325..3951b762cbddf 100644 --- a/mm/damon/stat.c +++ b/mm/damon/stat.c @@ -19,14 +19,17 @@ static int damon_stat_enabled_store( const char *val, const struct kernel_param *kp); +static int damon_stat_enabled_load(char *buffer, + const struct kernel_param *kp); + static const struct kernel_param_ops enabled_param_ops = { .set = damon_stat_enabled_store, - .get = param_get_bool, + .get = damon_stat_enabled_load, }; static bool enabled __read_mostly = IS_ENABLED( CONFIG_DAMON_STAT_ENABLED_DEFAULT); -module_param_cb(enabled, &enabled_param_ops, &enabled, 0600); +module_param_cb(enabled, &enabled_param_ops, NULL, 0600); MODULE_PARM_DESC(enabled, "Enable of disable DAMON_STAT"); static unsigned long estimated_memory_bandwidth __read_mostly; @@ -273,17 +276,23 @@ static void damon_stat_stop(void) damon_stat_context = NULL; } +static bool damon_stat_enabled(void) +{ + if (!damon_stat_context) + return false; + return damon_is_running(damon_stat_context); +} + static int damon_stat_enabled_store( const char *val, const struct kernel_param *kp) { - bool is_enabled = enabled; int err; err = kstrtobool(val, &enabled); if (err) return err; - if (is_enabled == enabled) + if (damon_stat_enabled() == enabled) return 0; if (!damon_initialized()) @@ -293,16 +302,17 @@ static int damon_stat_enabled_store( */ return 0; - if (enabled) { - err = damon_stat_start(); - if (err) - enabled = false; - return err; - } + if (enabled) + return damon_stat_start(); damon_stat_stop(); return 0; } +static int damon_stat_enabled_load(char *buffer, const struct kernel_param *kp) +{ + return sprintf(buffer, "%c\n", damon_stat_enabled() ? 'Y' : 'N'); +} + static int __init damon_stat_init(void) { int err = 0; -- 2.47.3