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 03721FF885D for ; Tue, 28 Apr 2026 10:31:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4CDA76B008A; Tue, 28 Apr 2026 06:31:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 47E6A6B008C; Tue, 28 Apr 2026 06:31:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3949E6B0092; Tue, 28 Apr 2026 06:31:36 -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 281F76B008A for ; Tue, 28 Apr 2026 06:31:36 -0400 (EDT) Received: from smtpin11.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id B9652A059D for ; Tue, 28 Apr 2026 10:31:35 +0000 (UTC) X-FDA: 84707598150.11.C12516F Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) by imf17.hostedemail.com (Postfix) with ESMTP id D467240002 for ; Tue, 28 Apr 2026 10:31:33 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=VPcuSwBQ; spf=pass (imf17.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.184 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1777372294; 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=GfD44pvjIJQiloqBwDkzUp2PEMv63WqNX+o/AM5Jdnc=; b=iIlMEE1hJsCM1VNM8+vGhKXtPk9sRoFRzOiscAxjRmrtMvJQgcIhrMUH2Xzqta6gM97MvT obW80kZEF8GvLa+Vmx6/IFebc32LPHElHkPqLpouaBOP16g+Kh+76+eytkWb+CvNMCHeuF K2YbRxFkh6hMbGDnp59VSNncjHK3biA= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=VPcuSwBQ; spf=pass (imf17.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.184 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1777372294; a=rsa-sha256; cv=none; b=thNsIuNcSb/Hg3EqcDiKkzvYVQblrMzk0bZF4E+DHI1SzpUOZ6+Zsep9klW4SuCr7QNJ5q aoJaYCMqowA7aTUENnUncY0E/S0hdUV04Ny24Y4z3F4b8UIPg2Svw/VYwzrrF1xy9ZstuM guEz3Ln1E4pz4qqL7YC6hd1Ia6ZsIyQ= 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=1777372291; 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=GfD44pvjIJQiloqBwDkzUp2PEMv63WqNX+o/AM5Jdnc=; b=VPcuSwBQvNR3K0qe6XdIc2exAZLvcygNpypa8DFTdzkJhnd8Jn1wWbqnSooLVIJwjdvrp3 g+qSW5heuurHzYUsJtRmcPy3OtNwMVL/UitrMBd7lXT40ymkElYnTjqEV/RltQE72mFhak obmj/4CKJzwT4/n/uwgdXo2NebuFA4o= From: Qi Zheng To: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, yosry@kernel.org Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng Subject: [PATCH v2] mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end() Date: Tue, 28 Apr 2026 18:31:08 +0800 Message-ID: <20260428103108.45719-1-qi.zheng@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: ub6rry8ecrouhrqydt7ksrbczh66ptz8 X-Rspamd-Queue-Id: D467240002 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1777372293-20009 X-HE-Meta: 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 z4lMkO59 GV6AU8W3FeMfzBME4nkcC4/4Ht153kXgChSPdgX+dbDPtN18AETVqUiZbZ9fZedQOJcxwrWhTwV9xP7ILgc7U92rk17WZ2+enVtbqB4vg5dRbBYd9094N6To+tcgKunBcaFIN0s08R62fT38wC3DotdYqQEBmWnRbSGrKeNUBYxgZFfn4Ti1Fz/mVtXcz2ds8Hum50zLW5C/9jyIna7Jeqg3iawB5lO/jcDIK+Ta5a+j2zO1bwVGhoQRCekNrFI19oAPJ6SJjYofHPTg+1mhuGDFJIXQ5E3jtZGwdf4lIWhjbndZGcGGJ28p5mA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Qi Zheng Currently, get_non_dying_memcg_start() and get_non_dying_memcg_end() both evaluate cgroup_subsys_on_dfl(memory_cgrp_subsys) independently to determine whether to acquire or release the RCU read lock. However, the result of cgroup_subsys_on_dfl() can change dynamically at runtime due to cgroup hierarchy rebinding (e.g., when the memory controller is moved between cgroup v1 and v2 hierarchies). This can cause the following warning: ===================================== WARNING: bad unlock balance detected! 7.0.0-next-20260420+ #83 Tainted: G W ------------------------------------- memcg-repro/270 is trying to release lock (rcu_read_lock) at: [] rcu_read_unlock+0x17/0x60 but there are no more locks to release! other info that might help us debug this: 1 lock held by memcg-repro/270: #0: ffff888102fa2088 (vm_lock){++++}-{0:0}, at: do_user_addr_fault+0x285/0x880 stack backtrace: CPU: 0 UID: 0 PID: 270 Comm: memcg-repro Tainted: G W 7.0.0-next-20260420+ # Tainted: [W]=WARN Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 Call Trace: ? rcu_read_unlock+0x17/0x60 dump_stack_lvl+0x77/0xb0 print_unlock_imbalance_bug+0xe0/0xf0 ? rcu_read_unlock+0x17/0x60 lock_release+0x21d/0x2a0 rcu_read_unlock+0x1c/0x60 do_pte_missing+0x233/0xb40 __handle_mm_fault+0x80e/0xcd0 handle_mm_fault+0x146/0x310 do_user_addr_fault+0x303/0x880 exc_page_fault+0x9b/0x270 asm_exc_page_fault+0x26/0x30 RIP: 0033:0x5590e4eb41ea Code: 61 cc 66 0f 6f e0 66 0f 61 c2 66 0f db cd 66 0f 69 e2 66 0f 6f d0 66 0f 69 d4 66 0f 61 0 RSP: 002b:00007ffcad25f030 EFLAGS: 00010202 RAX: 00005590e4eb8010 RBX: 00007ffcad260f7d RCX: 00007f73c474d44d RDX: 00005590e4eb80a0 RSI: 00005590e4eb503c RDI: 000000000000000f RBP: 00005590e4eb70a0 R08: 0000000000000000 R09: 00007f73c483a680 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffcad25f180 R14: 00005590e4eb6dd8 R15: 00007f73c4869020 ------------[ cut here ]------------ Fix this by explicitly tracking the RCU lock state, ensuring that rcu_read_unlock() in get_non_dying_memcg_end() is strictly paired with the lock acquisition, regardless of any runtime rebinding events. Fixes: 8285917d6f38 ("mm: memcontrol: prepare for reparenting non-hierarchical stats") Signed-off-by: Qi Zheng Acked-by: Shakeel Butt --- Changes in v2: - remove unnessary rcu_locked setting under !CONFIG_MEMCG_V1 (pointed by Shakeel Butt) - collect Acked-by mm/memcontrol.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c3d98ab41f1f1..eb55bace9f8c3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -805,12 +805,17 @@ static long memcg_state_val_in_pages(int idx, long val) * Used in mod_memcg_state() and mod_memcg_lruvec_state() to avoid race with * reparenting of non-hierarchical state_locals. */ -static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg) +static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg, + bool *rcu_locked) { - if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) + /* Rebinding can cause this value to be changed at runtime */ + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) { + *rcu_locked = false; return memcg; + } rcu_read_lock(); + *rcu_locked = true; while (memcg_is_dying(memcg)) memcg = parent_mem_cgroup(memcg); @@ -818,20 +823,21 @@ static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *me return memcg; } -static inline void get_non_dying_memcg_end(void) +static inline void get_non_dying_memcg_end(bool rcu_locked) { - if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) + if (!rcu_locked) return; rcu_read_unlock(); } #else -static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg) +static inline struct mem_cgroup *get_non_dying_memcg_start(struct mem_cgroup *memcg, + bool *rcu_locked) { return memcg; } -static inline void get_non_dying_memcg_end(void) +static inline void get_non_dying_memcg_end(bool rcu_locked) { } #endif @@ -865,12 +871,14 @@ static void __mod_memcg_state(struct mem_cgroup *memcg, void mod_memcg_state(struct mem_cgroup *memcg, enum memcg_stat_item idx, int val) { + bool rcu_locked; + if (mem_cgroup_disabled()) return; - memcg = get_non_dying_memcg_start(memcg); + memcg = get_non_dying_memcg_start(memcg, &rcu_locked); __mod_memcg_state(memcg, idx, val); - get_non_dying_memcg_end(); + get_non_dying_memcg_end(rcu_locked); } #ifdef CONFIG_MEMCG_V1 @@ -933,14 +941,15 @@ static void mod_memcg_lruvec_state(struct lruvec *lruvec, struct pglist_data *pgdat = lruvec_pgdat(lruvec); struct mem_cgroup_per_node *pn; struct mem_cgroup *memcg; + bool rcu_locked; pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); - memcg = get_non_dying_memcg_start(pn->memcg); + memcg = get_non_dying_memcg_start(pn->memcg, &rcu_locked); pn = memcg->nodeinfo[pgdat->node_id]; __mod_memcg_lruvec_state(pn, idx, val); - get_non_dying_memcg_end(); + get_non_dying_memcg_end(rcu_locked); } /** -- 2.20.1