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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D6C0ACD6E55 for ; Mon, 1 Jun 2026 16:15:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C832F6B0450; Mon, 1 Jun 2026 12:15:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C5AD36B0451; Mon, 1 Jun 2026 12:15:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B98546B0452; Mon, 1 Jun 2026 12:15:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id A89476B0450 for ; Mon, 1 Jun 2026 12:15:47 -0400 (EDT) Received: from smtpin28.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 47070140702 for ; Mon, 1 Jun 2026 16:15:47 +0000 (UTC) X-FDA: 84831844734.28.39B0635 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) by imf05.hostedemail.com (Postfix) with ESMTP id B28C210000D for ; Mon, 1 Jun 2026 16:15:45 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=UHPu02Cw; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf05.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.176 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780330545; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references:dkim-signature; bh=rQzi2gONxiIcDHLm2VrGnw9O4REpeifQom+6RrcJBmg=; b=zXHsswCoYyPBjGL3Yz0Woo1tHvx/JLNTG+5WKPjiu5S2+h2LOcI/o133MyBa7oBMsuGTKI IDesFboiza2KTnTKmBfyHw4HtBrmmM4mSsznhtWOaREy3RjeNKfXI5bygfbxvZqEBhNdqO WPt3hqkDf7BLOzqpwIjKipHQAAZyuFk= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=UHPu02Cw; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf05.hostedemail.com: domain of shakeel.butt@linux.dev designates 95.215.58.176 as permitted sender) smtp.mailfrom=shakeel.butt@linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780330545; b=UnpjGJLp9kNMueFAINQpGW10XE3BRc8pB8t3P/A0SH2LgFQOYwDbvtWK7NtGwOqTmnzpIU FXmqffksjNbPK5zjl2UsLKW0Byy+NBFNkSdXLKtxPkHFF7z83FWgw30fNqvVLAbUWtZUyp k+j2Mva/19WEF9Lg+MPQLMhLQH8QrFY= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780330543; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=rQzi2gONxiIcDHLm2VrGnw9O4REpeifQom+6RrcJBmg=; b=UHPu02CwuMbgjZG0+HMELc4RBe5U3EZ7RKAqtpyPIJnXvVryWYBOOtyJ7bZCGkqOgMiXHC xufUOXPsuX9osPAjao2KYXDh3t8t9BASS6p/vuIulI5fCZ3OLzGDdWQj/ym+QC2kyUbw8Q LtEq5I5DMjlJPvNettYkKG+F0+CQDlk= From: Shakeel Butt To: Andrew Morton Cc: Johannes Weiner , Dave Chinner , Roman Gushchin , Muchun Song , Qi Zheng , Kairui Song , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org Subject: [PATCH v2] mm/list_lru: drain before clearing xarray entry on reparent Date: Mon, 1 Jun 2026 09:15:01 -0700 Message-ID: <20260601161501.1444829-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B28C210000D X-Stat-Signature: iecofu48krptobpdehz8yhduj1196wqp X-Rspam-User: X-HE-Tag: 1780330545-247376 X-HE-Meta: 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 yEqzRNTz kF6a5kRlfIf47wH0NwEEy6Z/JziZdJKhUI2YdjjO9WFN5V52q43rZXaBkonu5SzDZUvvmxqM5neEvRv5wRKk1uaoqmab5lVvjeIPljmeGY7w1qR1mwcdYaB3QB7asTQC9Jq2Mtj0gFA59jjSeiYsy94dhI3hVV4xdMGW/WDRu1mFIXDa+mv3Q2NM2saMv8bPvsaWnY9bimXlWKZwoC2rVcskbcvK5UqMeps1bxQVsNYOawLwTfUYf/hBqYQtWKIHpdjHbipRGDol1y4BtBUpnGgZTs9EgAnaBfDq+ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: memcg_reparent_list_lrus() clears the dying memcg's xarray entry with xas_store(&xas, NULL) before reparenting its per-node lists into the parent. This opens a window where a concurrent list_lru_del() arriving for the dying memcg sees xa_load() == NULL, walks to the parent in lock_list_lru_of_memcg(), takes the parent's per-node lock, and calls list_del_init() on an item still physically linked on the dying memcg's list. If another in-flight thread holds the dying memcg's per-node lock at the same moment (another list_lru_del, or a list_lru_walk_one running an isolate callback), both threads modify ->next/->prev pointers on the same physical list under different locks. Adjacent items can corrupt each other's links. Fix it by reversing the order: reparent each per-node list and mark the child's list lru dead and then clear the xarray entry. Any concurrent list_lru op that finds the still-set xarray entry either takes the dying memcg's per-node lock (synchronizing with the drain) or sees LONG_MIN and walks to the parent, where the items now live. Fixes: fb56fdf8b9a2 ("mm/list_lru: split the lock to per-cgroup scope") Signed-off-by: Shakeel Butt Reported-by: Chris Mason Cc: stable@vger.kernel.org --- Changes since v1: - Use xa_erase_irq() instead of xa_erase() (Sashiko & Claude). - Added comment on CSS_DYING check in memcg_list_lru_alloc avoiding a new mlru allocation. mm/list_lru.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/mm/list_lru.c b/mm/list_lru.c index dd29bcf8eb5f..d454bce9a78e 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -473,26 +473,29 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren mutex_lock(&list_lrus_mutex); list_for_each_entry(lru, &memcg_list_lrus, list) { struct list_lru_memcg *mlru; - XA_STATE(xas, &lru->xa, memcg->kmemcg_id); /* - * Lock the Xarray to ensure no on going list_lru_memcg - * allocation and further allocation will see css_is_dying(). + * css_is_dying() check in memcg_list_lru_alloc() avoids + * allocating a new mlru since CSS_DYING is already set for this + * memcg a rcu grace period ago. */ - xas_lock_irq(&xas); - mlru = xas_store(&xas, NULL); - xas_unlock_irq(&xas); + mlru = xa_load(&lru->xa, memcg->kmemcg_id); if (!mlru) continue; /* - * With Xarray value set to NULL, holding the lru lock below - * prevents list_lru_{add,del,isolate} from touching the lru, - * safe to reparent. + * Reparent each per-node list and mark the child dead + * (LONG_MIN) before clearing xarray entry otherwise a + * concurrent list_lru_del() may corrupt the list if it arrives + * after xarray clear but before reparenting as + * lock_list_lru_of_memcg will acquire parent's lock while the + * item is still on child's list. */ for_each_node(i) memcg_reparent_list_lru_one(lru, i, &mlru->node[i], parent); + xa_erase_irq(&lru->xa, memcg->kmemcg_id); + /* * Here all list_lrus corresponding to the cgroup are guaranteed * to remain empty, we can safely free this lru, any further -- 2.53.0-Meta