From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8962AEB64DD for ; Wed, 2 Aug 2023 02:56:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231827AbjHBC4h (ORCPT ); Tue, 1 Aug 2023 22:56:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231706AbjHBC4e (ORCPT ); Tue, 1 Aug 2023 22:56:34 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C9F72722 for ; Tue, 1 Aug 2023 19:56:21 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id 3f1490d57ef6-c647150c254so860889276.1 for ; Tue, 01 Aug 2023 19:56:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1690944980; x=1691549780; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=J6cxPzKelBRogs1RcqlDIpKMeY4RfiCOB4MpGgBN/Dg=; b=Jrr8nzKXxGfH9rZ05coei/Z5XkXPQKYffsRvq0JJPMkpPWKSPML6OO06eZDIof3ZxE FqR3adURv8HbiY0CSWCrzORDmomvxAk0WLRY9cf18uCIkdSyJjl/VvbdCY4q9Wy7Oc4w +pskRXdmBEFfcC42q/5pqN3PxM0TzWr4gK4sE9xc5wu50UZc34qQkFTahmwhRGZJVytQ iQt96NsYT5jF6oFb+S9xqxKcAjWxbIwls+nZQCaZUiFG50rjkxYUVoWP/KSzWH+XfZJr RVj4ctwi+migEpHkjEJI3k5GUHjwOtKhv4c0gSFmtgVSST9QuZmYcyIVrwx+qWlaHlyG UnUQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690944980; x=1691549780; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=J6cxPzKelBRogs1RcqlDIpKMeY4RfiCOB4MpGgBN/Dg=; b=j/KJZ08S87CF+Dv2lgQEYpr+HMV+cNmAv/rvlp6o1j2v75ssqlBWRXwPYbQrJfmzZM yIVWOcPPBbhfqHCyTX1qayu2NYVL8e69bSMqzL2Lxt/svAvlPcMWlOVnpE5X0lH+Ujps nKjYlE+Xan7r2En5HUkiHB+1PJtz5o+eLdXqpeHPE/1JNrzr+u5d3l9OQDIilS1vphwp 6nCMnaaouUvkQRf6/tiqqbzv2pNBNhqZGeGzN/Lqpza1iLfTSt3dY8uS4vF7HDw0gFK/ ZK5aDCjSLbxOeuzlPjkLOcfgaABJZ3uADuMLxfpX4vbRR2Bji5zEH5Ih6/SwyEFrugpU vWuA== X-Gm-Message-State: ABy/qLZINZXh4okmW1tXYkmTxGalIe27BzBI7+FIwNMBCPN5kyYfRYg5 JocX0pzp74XJ7lyM7Mfxw1hp4NwCVuOB7PYV5Q== X-Google-Smtp-Source: APBJJlHvG4mc4jsYVOJYfZ7h42Tv/EwdyD/HOeVXUVvtcmr8y48s75g7rEDYvVAnOWGuPl5UYIq68sSDD86PJyMPYA== X-Received: from kalesh.mtv.corp.google.com ([2620:15c:211:201:aa5f:ff75:318:255]) (user=kaleshsingh job=sendgmr) by 2002:a25:b084:0:b0:bd5:dc2d:9d7f with SMTP id f4-20020a25b084000000b00bd5dc2d9d7fmr167401ybj.4.1690944980290; Tue, 01 Aug 2023 19:56:20 -0700 (PDT) Date: Tue, 1 Aug 2023 19:56:03 -0700 In-Reply-To: <20230802025606.346758-1-kaleshsingh@google.com> Mime-Version: 1.0 References: <20230802025606.346758-1-kaleshsingh@google.com> X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog Message-ID: <20230802025606.346758-2-kaleshsingh@google.com> Subject: [PATCH v2 2/3] mm-unstable: Multi-gen LRU: Avoid race in inc_min_seq() From: Kalesh Singh To: yuzhao@google.com, akpm@linux-foundation.org Cc: surenb@google.com, android-mm@google.com, kernel-team@android.com, Kalesh Singh , stable@vger.kernel.org, Aneesh Kumar K V , Matthias Brugger , AngeloGioacchino Del Regno , "Jan Alexander Steffens (heftig)" , Oleksandr Natalenko , Brian Geffon , Steven Barrett , Suleiman Souhlal , Qi Zheng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org inc_max_seq() will try to inc_min_seq() if nr_gens == MAX_NR_GENS. This is because the generations are reused (the last oldest now empty generation will become the next youngest generation). inc_min_seq() is retried until successful, dropping the lru_lock and yielding the CPU on each failure, and retaking the lock before trying again: while (!inc_min_seq(lruvec, type, can_swap)) { spin_unlock_irq(&lruvec->lru_lock); cond_resched(); spin_lock_irq(&lruvec->lru_lock); } However, the initial condition that required incrementing the min_seq (nr_gens == MAX_NR_GENS) is not retested. This can change by another call to inc_max_seq() from run_aging() with force_scan=true from the debugfs interface. Since the eviction stalls when the nr_gens == MIN_NR_GENS, avoid unnecessarily incrementing the min_seq by rechecking the number of generations before each attempt. This issue was uncovered in previous discussion on the list by Yu Zhao and Aneesh Kumar [1]. [1] https://lore.kernel.org/linux-mm/CAOUHufbO7CaVm=xjEb1avDhHVvnC8pJmGyKcFf2iY_dpf+zR3w@mail.gmail.com/ Fixes: d6c3af7d8a2b ("mm: multi-gen LRU: debugfs interface") Cc: stable@vger.kernel.org Cc: Yu Zhao Cc: Aneesh Kumar K V Cc: Andrew Morton Signed-off-by: Kalesh Singh --- Changes in v2: - Add Fixes tag and cc stable mm/vmscan.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 489a4fc7d9b1..6eecd291756c 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4439,7 +4439,7 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan) int prev, next; int type, zone; struct lru_gen_folio *lrugen = &lruvec->lrugen; - +restart: spin_lock_irq(&lruvec->lru_lock); VM_WARN_ON_ONCE(!seq_is_valid(lruvec)); @@ -4450,11 +4450,12 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan) VM_WARN_ON_ONCE(!force_scan && (type == LRU_GEN_FILE || can_swap)); - while (!inc_min_seq(lruvec, type, can_swap)) { - spin_unlock_irq(&lruvec->lru_lock); - cond_resched(); - spin_lock_irq(&lruvec->lru_lock); - } + if (inc_min_seq(lruvec, type, can_swap)) + continue; + + spin_unlock_irq(&lruvec->lru_lock); + cond_resched(); + goto restart; } /* -- 2.41.0.255.g8b1d071c50-goog