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Tue, 01 Jul 2025 11:52:51 -0700 (PDT) Received: from localhost ([2a03:2880:25ff:5::]) by smtp.gmail.com with ESMTPSA id 00721157ae682-71515c05cc4sm21223347b3.49.2025.07.01.11.52.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Jul 2025 11:52:51 -0700 (PDT) From: Joshua Hahn To: Dan Carpenter Cc: linux-mm@kvack.org, kees@ijzerbout.nl Subject: Re: [bug report] mm/mempolicy: skip extra call to __alloc_pages_bulk in weighted interleave Date: Tue, 1 Jul 2025 11:52:48 -0700 Message-ID: <20250701185249.557716-1-joshua.hahnjy@gmail.com> X-Mailer: git-send-email 2.47.1 In-Reply-To: <22b9509b-3d92-4ecd-91b4-7a08c1da956c@sabinyo.mountain> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: oke4i1dd6nc7ci5taixioprabusxnuiw X-Rspamd-Queue-Id: 2F75412000F X-Rspamd-Server: rspam11 X-Rspam-User: X-HE-Tag: 1751395972-802213 X-HE-Meta: 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 8s/aRncb 9PGvVXzCm3mKDVvWNTdj6dUVwvHyRVvcew3Qo308fXOj3+XhEfELo7uJTPIR2EPA7OBO9A//ku/7YYZwPA48fMhWH3GCQQuYcqUK6gpW5BZCks5gX1XFnFZO4vMem6B9J4jPjE5BuQOj6rqs0cvnX0uWzFfQPYFDqUpJGgOQik/hmVyZZNnBOg2m0cA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: + Cc Kees, who also reported this yesterday! On Tue, 1 Jul 2025 13:07:53 -0500 Dan Carpenter wrote: > Hello Joshua Hahn, > > Commit 72cf498b9e8a ("mm/mempolicy: skip extra call to > __alloc_pages_bulk in weighted interleave") from Jun 26, 2025 > (linux-next), leads to the following Smatch static checker warning: > > mm/mempolicy.c:2641 alloc_pages_bulk_weighted_interleave() > error: uninitialized symbol 'i'. [...snip...] > 2593 /* Continue allocating from most recent node and adjust the nr_pages */ > 2594 node = me->il_prev; > 2595 weight = me->il_weight; > 2596 if (weight && node_isset(node, nodes)) { > 2597 if (rem_pages <= weight) { > 2598 node_pages = rem_pages; > 2599 me->il_weight -= node_pages; > 2600 goto allocate; > > i is not initialized here. > > 2601 } > 2602 carryover = weight; > 2603 } > 2604 /* clear active weight in case of an allocation failure */ > 2605 me->il_weight = 0; > 2606 prev_node = node; > 2607 > 2608 /* create a local copy of node weights to operate on outside rcu */ > 2609 weights = kzalloc(nr_node_ids, GFP_KERNEL); > 2610 if (!weights) > 2611 return 0; > 2612 > 2613 rcu_read_lock(); > 2614 state = rcu_dereference(wi_state); > 2615 if (state) { > 2616 memcpy(weights, state->iw_table, nr_node_ids * sizeof(u8)); > 2617 rcu_read_unlock(); > 2618 } else { > 2619 rcu_read_unlock(); > 2620 for (i = 0; i < nr_node_ids; i++) > 2621 weights[i] = 1; > 2622 } > 2623 > 2624 /* calculate total, detect system default usage */ > 2625 for_each_node_mask(node, nodes) > 2626 weight_total += weights[node]; > 2627 > 2628 /* > 2629 * Calculate rounds/partial rounds to minimize __alloc_pages_bulk calls. > 2630 * Track which node weighted interleave should resume from. > 2631 * Account for carryover. It is always allocated from the first node. > 2632 * > 2633 * if (rounds > 0) and (delta == 0), resume_node will always be > 2634 * the node following prev_node and its weight. > 2635 */ > 2636 rounds = (rem_pages - carryover) / weight_total; > 2637 delta = (rem_pages - carryover) % weight_total; > 2638 resume_node = next_node_in(prev_node, nodes); > 2639 resume_weight = weights[resume_node]; > 2640 node = carryover ? prev_node : next_node_in(prev_node, nodes); > --> 2641 for (i = 0; i < nnodes; i++) { > ^^^^^^^^^^^^^^^ > Uninitialized variable. In production people should use the config to > zero out stack variables but I always encourage developers to use > CONFIG_INIT_STACK_ALL_PATTERN=y in their testing. Hello Dan, Thank you for your feedback! I will look into the config, I am sure it will be very helpful for future patches that I work on. As for this specific uninitialized variable, Kees brought it up in [1], and I'll be revising this in future versions. Sorry for the bad coding style, I think I got a litle too eager to make the code look prettier. I hope you have a great day! Joshua [1] https://lore.kernel.org/all/7c1180f4-923c-4138-b756-618cb5d597ac@ijzerbout.nl/ Sent using hkml (https://github.com/sjp38/hackermail)