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Fri, 03 Apr 2026 01:31:26 -0700 (PDT) Received: from celestia.taila51cc2.ts.net ([2402:1980:898b:301c:d085:a35:99e7:ffec]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b27472d280sm54193015ad.17.2026.04.03.01.31.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Apr 2026 01:31:25 -0700 (PDT) From: Liew Rui Yan To: aethernet65535@gmail.com Cc: damon@lists.linux.dev, linux-mm@kvack.org, sj@kernel.org, stable@vger.kernel.org, yanquanmin1@huawei.com Subject: Re: (sashiko review) [PATCH v3 1/2] mm/damon/lru_sort: validate min_region_size to be power of 2 Date: Fri, 3 Apr 2026 16:31:25 +0800 Message-ID: <20260403083125.5654-1-aethernet65535@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260403052837.58063-2-aethernet65535@gmail.com> References: <20260403052837.58063-2-aethernet65535@gmail.com> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Forwarding Sashiko review for doing discussions via mails. # review url: https://sashiko.dev/#/patchset/20260403052837.58063-2-aethernet65535@gmail.com # start of sashiko.dev inline review commit 525a0116b6d91612e679b30ae84e489a7540edbf Author: Liew Rui Yan mm/damon/lru_sort: validate min_region_size to be power of 2 This commit adds an early check in damon_lru_sort_apply_parameters() to ensure min_region_sz is a power of 2. This prevents kdamond from unexpectedly terminating when given an invalid addr_unit. > diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c > index 554559d729760..3fd176ef9d9c1 100644 > --- a/mm/damon/lru_sort.c > +++ b/mm/damon/lru_sort.c > @@ -294,6 +294,11 @@ static int damon_lru_sort_apply_parameters(void) > param_ctx->addr_unit = addr_unit; > param_ctx->min_region_sz = max(DAMON_MIN_REGION_SZ / addr_unit, 1); > > + if (!is_power_of_2(param_ctx->min_region_sz)) { > + err = -EINVAL; > + goto out; > + } > + Instead of adding this early check here, could this be resolved by fixing the stateless validation in damon_commit_ctx() directly? Looking at damon_commit_ctx(), it currently sets dst->maybe_corrupted = true before checking if src->min_region_sz is a power of 2: int damon_commit_ctx(struct damon_ctx *dst, struct damon_ctx *src) { int err; dst->maybe_corrupted = true; if (!is_power_of_2(src->min_region_sz)) return -EINVAL; ... } When this validation fails, it leaves the active context marked as corrupted without making any state changes, which causes the kdamond thread to terminate permanently. Moving the stateless is_power_of_2() check above dst->maybe_corrupted = true would resolve the regression for all current and future callers without requiring duplicated validation logic at every call site. Does this missing validation also affect mm/damon/sysfs.c? When a user starts DAMON via state_store() -> damon_sysfs_turn_damon_on(), the code calls damon_sysfs_build_ctx(). This calculates min_region_sz and then directly calls damon_start(), bypassing damon_commit_ctx() entirely. Because this bypasses the is_power_of_2() checks, kdamond can actively run with a non-power-of-2 min_region_sz. Core DAMON operations like damon_set_regions() use ALIGN() and ALIGN_DOWN() with min_region_sz, which perform bitwise masking that requires the alignment parameter to be a power of 2. Could this allow userspace to trigger incorrect address boundaries, massive unsigned underflows, or infinite loops during region splitting? > if (!damon_lru_sort_mon_attrs.sample_interval) { > err = -EINVAL; > goto out; # end of sashiko.dev inline review # review url: https://sashiko.dev/#/patchset/20260403052837.58063-2-aethernet65535@gmail.com # # hkml [1] generated a draft of this mail. It can be regenerated # using below command: # # hkml patch sashiko_dev --for_forwarding \ # 20260403052837.58063-2-aethernet65535@gmail.com # # [1] https://github.com/sjp38/hackermail