From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792464007; b=mgklfd6MnApyRJTGmSGELXe4NAYz6OqZtbdFVY7oM521JUt8l6ViM22OgCi7Mc1Nrbtb iiEaSe3UZFc62ZyYwM1IfwOftfxs1JvD27M+Y+0gVfyCgR6ZYFoQHzwj0FtJtsi9R5S55 +JAQe8m0GxNKRBVQ+ZmhIKM2szgnnUCMD2f2X4DPZbF/h2no+uqC2649E8W9OvEhsKM/q 3bfcZ7ErMF5+8xX4F9soilOSG8fY4UqI2wndfWoSN0DO1ZnEmW4cNrSLXblraI5wSBZuF mryCceYh0W2uLtpc/AYv/5FllHRs4Ty4zmRA5RY9EwLQkrGUkD+6sqdi/iftBh8GYYw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792464007; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Transfer-Encoding; bh=60QPBhNMCngRfmcAjrxpcv4Imf6U8Bv5IKWR7KuqOvs=; b=eeAN0awRuJJ6mvSlK9aTCHAtizQSoCyH1ONvc73U9IrX6YWjxmE8otqr4klv7eT7rUSo xqyMJgxk8zjDgLybn6WnjmeOc9g2KuboLnMGu4IRoJh+9OjhPsWxc9YcNcYXANxHAJA8Z Vy7SWI+Sv4LQr1oZ03umTz1Cv9DAsk7tXyxDbLTk9n2QvRQSvw9CZJHmC1wna5JYvBmmj 5uHTkmCQfY3XVUsT6C+sR5oF5hmxZmdyAHK/6X4c7s4qUIBrIZp/hI5GNfl5kRlw75+ZF I6zZ244dTbGc0U1+qxFbFzTdt+VEh38gcisPP3UmCe6EkG7eyo0e1qQO8u33q7W7TGQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Xyqgyjm5; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D84A8606A319; Tue, 20 Oct 2026 02:40:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Xyqgyjm5 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3F9241F000C4; Tue, 20 Oct 2026 02:40:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792464006; bh=60QPBhNMCngRfmcAjrxpcv4Imf6U8Bv5IKWR7KuqOvs=; h=From:To:Cc:Subject:Date; b=Xyqgyjm5aAEUx7O1C9+9sZ9HoyLu1TowKrpLnSkIE2mnYWjuicwO9PecBk4neY/QR qOEt0O820lHWWZw3hrx+f6My1KevhlIB/FNNOapdeq8Uub3voWMxb2nb4Sc5p+QgMB hncjtTQ25QsrGw6AmtFQKsg4WlFMZsuz0ekg82bW9XeertI7dDcyOhKPjRqT0vbvqU eGdfGNIsslgL/v044qhPF79CYZ+XN03Gbjj8gygXSkwtNGkAyAiXvg8GcgzJb4m1yz qyhk3F4OfK1NbUu5zoNOmc2UuwaXjO8xZTM4+7XL7MF6zv+DSxIYaU908k6iF2gqTW 4cycCLMbtUWnw== From: SJ Park To: Andrew Morton Cc: SJ Park , stable@vger.kernel.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] mm/damon/core: remove unreachable damos charge_{target,addr}_from Date: Mon, 19 Oct 2026 19:39:56 -0700 Message-ID: <20261020023958.108276-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 X-Mailing-List: damon@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit damos_quota->charge_{target,addr}_from saves the target and region the scheme's quota limit is reached. damos_skip_charged_region() skips the target and regions before the point. The target that was assigned to charge_target_from could be dynamically removed from the context by the runtime parameters update (aka commit) feature. In this case, damos_skip_charged_region() cannot find if the point is passed or not, so the scheme is effectively disabled. Similarly, the user could also remove all the regions of the target using the runtime parameters update feature. It would be uncommon to do that, but it is a supported feature. Because the skip pointer detection logic (damos_skip_charged_region()) works for each region of targets, this result in the logic is entirely skipped and the scheme is effectively disabled again. The user impact is that the DAMOS scheme could suddenly stop working under certain uses of the runtime parameters update feature. It could surprise users. No crash or leak happens though. Users could also simply work around by re-installing the scheme. Catch the corner cases in damos_adjust_quota() and reset the pointers. Fixes: da87878010e5 ("mm/damon/sysfs: support online inputs update") Cc: # 5.19.x Closes: https://sashiko.dev/#/bug/linux-cd0c55fc-0cc8-45d8-9637-3334811c49b8 Signed-off-by: SJ Park --- Changes from RFC - RFC: https://lore.kernel.org/20261019143713.98610-1-sj@kernel.org - Drop RFC tag. mm/damon/core.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index 479169dc9ac75..eb1fcdabc0075 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -3383,6 +3383,26 @@ static void damos_trace_esz(struct damon_ctx *c, struct damos *s, trace_damos_esz(cidx, sidx, quota->esz); } +static void damos_fix_stale_charge_pointers(struct damon_ctx *c, + struct damos *s) +{ + struct damos_quota *quota; + struct damon_target *t; + + quota = &s->quota; + if (!quota->charge_target_from) + return; + damon_for_each_target(t, c) { + if (t == quota->charge_target_from) { + if (damon_nr_regions(t) > 0) + return; + break; + } + } + quota->charge_target_from = NULL; + quota->charge_addr_from = 0; +} + static void damos_adjust_quota(struct damon_ctx *c, struct damos *s) { struct damos_quota *quota = &s->quota; @@ -3418,6 +3438,8 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s) damos_trace_esz(c, s, quota); } + damos_fix_stale_charge_pointers(c, s); + if (damos_quota_is_full(quota, c->min_region_sz)) return; if (!c->ops.get_scheme_score) base-commit: e558ba2a16a47baf6b8e76bb11e92eb92a491e3a -- 2.47.3