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=1792456892; b=xwB5y20nDLUe94XERWtSqrR0gaA2QWS/zmjluppROpJW/bEAmKgNCNRuWMyM07aPpve7 AMdU4iRQHfLsV+nuSW0qlTaCVOcgtxt8JzQ+VyVXno7kDJhdupOEFL2+gr0XkDhaJE1JC SWB0XL+V9Q+6xhDwA0x5/Z8oUQQniSqQHJavLO2KkO/mw5RafFHiKFFvBG/2qAFB0wKKX 5DqBzQD+MagC9FrGi/5LIcSksF3UaRVFUuH2QYpKS3txYh/gXI+lNXeOzfnkYeR6/ES7R MtEbS+BryV33n+xgBOekiTTftMIcS94UlbpSN8ftUZhSTz2GcmR6H1Tzpf20frOKAoA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792456892; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Transfer-Encoding; bh=9m+CklygXiF/Y3wz9sotcxoYMguOY3YvD18SzXdCUOg=; b=CruF0OLkuJFPTcfDjiq9v1RTkNEodoH9+/u9k17KIYj/IEZsJbZS9o8P5HOFHlQ7CJvy 2GLnTZYyQnPzk5V/KmqxiWTzBygJW/aJ8q6pz/rpqyhCKe89Qjk2RbTyI67bDOEy7hKta Ylf0DIY3oMwBoIz00Qbcl8U+33c6pSHi2at1wMkN9NDj2zEvR0Icz6AEVzCTV9SMm8IMo I2SH2j2T/F8SQT19sHj0DIGEnOpTdiUlJ6uY9lc6YKouoPqs1wYL7tFzb+FYMCpiVvNO9 wdqhqsMLPJTuY9umbB9K6VVAN6aapTVwIoyLT9t++wWqPahe1BW2ytRwt6WznGEzrjA== 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=erRlPRNc; 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 8FB43606A319; Tue, 20 Oct 2026 00:41:32 +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=erRlPRNc Received: by smtp.kernel.org (Postfix) with ESMTPSA id E4BEB1F000C4; Tue, 20 Oct 2026 00:41:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792456892; bh=9m+CklygXiF/Y3wz9sotcxoYMguOY3YvD18SzXdCUOg=; h=From:To:Cc:Subject:Date; b=erRlPRNc32l3KGSD/8lf7EP4fmsIbQeF9K5KSK3is6u61gURDZA8QYKz4TsU9Zg71 RvT5ostrfK93nZoxMclI1uGwuNdRGZutakIZ0iitfHzuIZ8X4vGn5RV+VqhzE10h0L Xrw0bmHzKuHR6tzCjP2LRC5Kua86B6qLe5MHiTjfyPCVSS2EFaVtDjSL/ghxtLy62l GJ93bcu22RcBrYZKlxZWi3/xMDNuVAa7AaEJwSWBrJO2A6Zj8dUbqSsVlRPvd8ufSf YvPX0bGWC8btTOVDBW/vMqpXeHiiwclEV4hkJyxbsvmku0JW7/VIxUv4pQPmwCraaL 7Mh3mm8OT4qmw== 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: filter out damos address filter-split failed region Date: Mon, 19 Oct 2026 17:41:18 -0700 Message-ID: <20261020004119.106690-1-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 When an address type DAMOS filter is configured, DAMOS tries to split the region for the filter range, and apply DAMOS action to the filter-in region. The split operation (damon_split_region_at()) could fail from allocation failure under extreme memory pressure. In the case, DAMOS action could be applied more or less than expected, ignoring the address filter. The issue only rarely happens under extreme memory pressure. No crash or leak happens. Occasionally not applying the action to a few regions shouldn't be a real problem. But applying the action to a region that the user has excluded via address filter could be a surprise depending on the use case. It is only theoretical. No such real case is found yet. Filter out the entire region if the split is failed. Update damos_filter_match() signature to receive the error from split. Also update kunit tests for the updated signature. The issue was discovered [1] by sashiko. [1] https://lore.kernel.org/20260801203121.117449-1-sj@kernel.org Fixes: ab9bda001b68 ("mm/damon/core: introduce address range type damos filter") Cc: # 6.6.x Signed-off-by: SJ Park --- Changes from RFC v2 - RFC v2: https://lore.kernel.org/20261019133856.86835-1-sj@kernel.org - Drop RFC tag. Changes from RFC - RFC: https://lore.kernel.org/20261018220253.158238-1-sj@kernel.org - Handle failure in another split operation in damos_filter_match(). mm/damon/core.c | 16 ++++++++++++---- mm/damon/tests/core-kunit.h | 11 ++++++----- 2 files changed, 18 insertions(+), 9 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index b63e60ef89901..479169dc9ac75 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2551,13 +2551,14 @@ static void damos_update_stat(struct damos *s, static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t, struct damon_region *r, struct damos_filter *filter, - unsigned long min_region_sz) + unsigned long min_region_sz, int *err) { bool matched = false; struct damon_target *ti; int target_idx = 0; unsigned long start, end, wsum; + *err = 0; switch (filter->type) { case DAMOS_FILTER_TYPE_TARGET: damon_for_each_target(ti, ctx) { @@ -2583,12 +2584,13 @@ static bool damos_filter_match(struct damon_ctx *ctx, struct damon_target *t, } /* start before the range and overlap */ if (r->ar.start < start) { - damon_split_region_at(t, r, start - r->ar.start); + *err = damon_split_region_at(t, r, + start - r->ar.start); matched = false; break; } /* start inside the range */ - damon_split_region_at(t, r, end - r->ar.start); + *err = damon_split_region_at(t, r, end - r->ar.start); matched = true; break; case DAMOS_FILTER_TYPE_PROBE_HITS_WSUM: @@ -2607,10 +2609,16 @@ static bool damos_core_filter_out(struct damon_ctx *ctx, struct damon_target *t, struct damon_region *r, struct damos *s) { struct damos_filter *filter; + bool matching; + int err; s->core_filters_allowed = false; damos_for_each_core_filter(filter, s) { - if (damos_filter_match(ctx, t, r, filter, ctx->min_region_sz)) { + matching = damos_filter_match(ctx, t, r, filter, + ctx->min_region_sz, &err); + if (err) + return true; + if (matching) { if (filter->allow) s->core_filters_allowed = true; return !filter->allow; diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h index 3fbb4e4e36fac..43e2f950f8ff4 100644 --- a/mm/damon/tests/core-kunit.h +++ b/mm/damon/tests/core-kunit.h @@ -1783,6 +1783,7 @@ static void damos_test_filter_out(struct kunit *test) struct damon_target *t; struct damon_region *r, *r2; struct damos_filter *f; + int err; f = damos_new_filter(DAMOS_FILTER_TYPE_ADDR, true, false); if (!f) @@ -1803,27 +1804,27 @@ static void damos_test_filter_out(struct kunit *test) damon_add_region(r, t); /* region in the range */ - KUNIT_EXPECT_TRUE(test, damos_filter_match(NULL, t, r, f, 1)); + KUNIT_EXPECT_TRUE(test, damos_filter_match(NULL, t, r, f, 1, &err)); KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1); /* region before the range */ r->ar.start = 1; r->ar.end = 2; KUNIT_EXPECT_FALSE(test, - damos_filter_match(NULL, t, r, f, 1)); + damos_filter_match(NULL, t, r, f, 1, &err)); KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1); /* region after the range */ r->ar.start = 6; r->ar.end = 8; KUNIT_EXPECT_FALSE(test, - damos_filter_match(NULL, t, r, f, 1)); + damos_filter_match(NULL, t, r, f, 1, &err)); KUNIT_EXPECT_EQ(test, damon_nr_regions(t), 1); /* region started before the range */ r->ar.start = 1; r->ar.end = 4; - KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f, 1)); + KUNIT_EXPECT_FALSE(test, damos_filter_match(NULL, t, r, f, 1, &err)); /* filter should have split the region */ KUNIT_EXPECT_EQ(test, r->ar.start, 1); KUNIT_EXPECT_EQ(test, r->ar.end, 2); @@ -1839,7 +1840,7 @@ static void damos_test_filter_out(struct kunit *test) r->ar.start = 2; r->ar.end = 8; KUNIT_EXPECT_TRUE(test, - damos_filter_match(NULL, t, r, f, 1)); + damos_filter_match(NULL, t, r, f, 1, &err)); /* filter should have split the region */ KUNIT_EXPECT_EQ(test, r->ar.start, 2); KUNIT_EXPECT_EQ(test, r->ar.end, 6); base-commit: c120c766883129cc62ff62a5c2b531625d1e5d2c -- 2.47.3