From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 531E353D0DB for ; Tue, 8 Sep 2026 12:57:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788872223; cv=none; b=R5mvE8YC/2krasAw6jKbeuvioKMO1hFY1zX/to8hODZ0esaeNz1Rxt9geE8E5kIIYorp8b8zhxyjFLhA1QSJBUYBUUgxkK3cdkZgddNnrLdvYaO43+Am525sDfDG2LZnjCFxj5CI+/6GbCuV9kxCR1JB5wNiCc5ODiEt6AsCMXg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788872223; c=relaxed/simple; bh=G6fdwumSMBTKMDa40QKyMs2As/ghv/M2isTr58pgmfs=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=Wvwbgw0ELKgzG0SJVCQpkkJGXOBHUSDM6mJzlOM0vFjXMeS9HBJtcOJyQ298xKlbPP7p9s/Xd3wb3yjXJR2ToE5krz5zcXTkuWnIbe+9trVwglMieYpSXLy3yo4JEJP3xi4SoLN8fr4se6IDmQMQFiP3SgybQc79AXXrNlpkYAU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=owhMtco4; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="owhMtco4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AAF4D1F00A3D; Tue, 8 Sep 2026 12:57:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788872221; bh=dKkcG6PdXGXdfPRelxu+Mb2S4p8i9BtKHvVo3xUPQpM=; h=Subject:To:Cc:From:Date; b=owhMtco4Yp2LUo2ErI2jdznBk1LBsGSDkx4d7fys5qJfq6W3zqWvl+/q4sQcyaeOR qF5raelI+bVS8cSk7SAJ1+TzEVeu3qqoFcVm7lyhRslCj27NbzvzuCuPdufv7VnJFH o2Mg0T7qFWz9QnwkmytI+mxMxkfRDIsBw2kQ+rNo= Subject: FAILED: patch "[PATCH] mm/damon/core: avoid infinite kdamond_merge_regions()" failed to apply to 6.18-stable tree To: sj@kernel.org,akpm@linux-foundation.org,stable@vger.kernel.org Cc: From: Date: Tue, 08 Sep 2026 14:52:31 +0200 Message-ID: <2026090831-drinkable-maybe-5e01@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y git checkout FETCH_HEAD git cherry-pick -x 123e4619ab6c8ab1c4cb1d7a58311a2af13929cd # git commit -s git send-email --to '' --in-reply-to '2026090831-drinkable-maybe-5e01@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 123e4619ab6c8ab1c4cb1d7a58311a2af13929cd Mon Sep 17 00:00:00 2001 From: SJ Park Date: Tue, 14 Jul 2026 20:09:56 -0700 Subject: [PATCH] mm/damon/core: avoid infinite kdamond_merge_regions() internal loop Patch series "mm/damon: unurgent fixes for infinite loop, NULL de-ref and races", v1.1. Sashiko found a few issues in DAMON that could cause infinite loop, NULL dereference and monitoring results degradation. The first two sounds scary but the infinite loop happens only under unreasonable user setup. The NULL dereference is only in a unit test. Monitoring results degradation is trivial since it is only best-effort, and those happens from only unlikely races. Still those are bugs that better to fix if possible. Fix those. This patch (of 6): Due to online parameter update like events, the number of DAMON regions could be higher than the user-set upper limit. kdamond_merge_regions() repeats merge regions until the number meets the limit, while doubling the merge threshold up to the theoretical maximum threshold. It is tried only up to the theoretical maximum threshold because even the aggressive merging can fail from reducing the number of regions under the user-defined upper limit. For example, there could be many user-defined non-contiguous regions that cannot be merged. The threshold based loop break condition is evaluated by comparing the threshold for the next merging try against the theoretical maximum threshold. If max_thres is larger than UINT_MAX / 2, doubling the threshold could make it overflow, and bypass the loop break condition. In the case, if the number of regions cannot be reduced under the upper limit like explained above, the loop will run infinitely. Prevent the case by doing the break condition check before doubling the threshold. Also, prevent the threshold exceeding the maximum threshold, as it could overflow and apply the wrong merge threshold. This issue is unlikely to occur in real world, since having the max_thres higher than UINT_MAX / 2 require unrealistically large aggregation intervals compared to the sampling interval. Also, it requires an unrealistically large number of uncontiguous regions setup. Nonetheless, the consequence is bad and the fix is simple. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260715031002.108504-1-sj@kernel.org Link: https://lore.kernel.org/20260715031002.108504-2-sj@kernel.org Link: https://lore.kernel.org/20260709145425.96247-1-sj@kernel.org [1] Fixes: 310d6c15e910 ("mm/damon/core: merge regions aggressively when max_nr_regions is unmet") Signed-off-by: SJ Park Cc: # 6.10.x Signed-off-by: Andrew Morton diff --git a/mm/damon/core.c b/mm/damon/core.c index 6c4215cc809e..603b102ff80f 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -3372,7 +3372,7 @@ static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold, max_thres = c->attrs.aggr_interval / (c->attrs.sample_interval ? c->attrs.sample_interval : 1); - do { + while (true) { nr_regions = 0; damon_for_each_target(t, c) { damon_merge_regions_of(t, threshold, sz_limit, c, @@ -3380,9 +3380,14 @@ static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold, nr_regions += damon_nr_regions(t); } count_age = false; - threshold = max(1, threshold * 2); - } while (nr_regions > c->attrs.max_nr_regions && - threshold / 2 < max_thres); + if (nr_regions <= c->attrs.max_nr_regions || + max_thres <= threshold) + break; + if (threshold < max_thres / 2) + threshold = max(1, threshold * 2); + else + threshold = max_thres; + } } #ifdef CONFIG_DAMON_DEBUG_SANITY