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 53834FF8864 for ; Tue, 28 Apr 2026 03:07:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 939AF6B0088; Mon, 27 Apr 2026 23:07:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8C21C6B0092; Mon, 27 Apr 2026 23:07:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 78A166B0093; Mon, 27 Apr 2026 23:07:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 60FD96B0088 for ; Mon, 27 Apr 2026 23:07:15 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id E9C968B82D for ; Tue, 28 Apr 2026 03:07:14 +0000 (UTC) X-FDA: 84706478388.12.D42FB45 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) by imf12.hostedemail.com (Postfix) with ESMTP id 3904C40002 for ; Tue, 28 Apr 2026 03:07:12 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=R5+J33wq; spf=pass (imf12.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.188 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=1777345633; 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=lj79AkiwhWz5e6xPBu5nsEPq2wpNV8VJo+9BmZxFVVE=; b=pzzZWF6G12LKTCljCYqESrVzhWOyXGr1SiD3+vvvsSsQAoQ00eIt4hsh/sbDVL/0xWHI6j Gd99s76qxz7Jf8mKQMR43rtuLAd26+YmR0hBT/3/o4SrYcPpl+PHid/qn7xfNWO5oyo5M/ 0i4xeKg3uHXFYpnqQk8Nk1YUZsx+0pc= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=R5+J33wq; spf=pass (imf12.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.188 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=1777345633; a=rsa-sha256; cv=none; b=i4Qz8XsgXc/HZGil2TKWmRBkHJdXzUbyJFK+zTBTSRcZhU8RhFFGVh+CgVmojcXoV+f0Wm ji5Enk7V37CncVXaGaJEtmarhu01/6nUoYcU+P63cHBenmT8c52VHh6oyXtypZ4jU42UBU LdPqp5Bs1cQlvW1uUL6Fy8ugUYajsCo= 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=1777345631; 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=lj79AkiwhWz5e6xPBu5nsEPq2wpNV8VJo+9BmZxFVVE=; b=R5+J33wqgrfyTP7mprG8tRtRvDSbVvl+WagRmGAVETaKc5A1vuK870hHrRk0d7yCYitD4Q t7cTXJJke6zsYX3ufm93nuVu/aYQ3FdD8nkQxGfTzRRtgoc+gzWg3wEfXsFwWkEzWXnpcu BE7eHp7UYSi+Wfp0+VcFtTWHF2BxzUM= 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] mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end() Date: Tue, 28 Apr 2026 11:06:21 +0800 Message-ID: <20260428030621.94470-1-qi.zheng@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3904C40002 X-Stat-Signature: xg6e5ycppzwarkeckppnjr3k59xiqah3 X-HE-Tag: 1777345632-307838 X-HE-Meta: U2FsdGVkX18Q0J1qTn1r5ZA/BZgYdhirFT+XZJwLvt3YLWTOHh9JzS9FtswSAlmzNarfz41iZhRShINj3jmALg+iJ7/IxGT4AHtOATW3meVdFMMPQKTbZPbSRsEmP+WZo4mlnjK9Keug5mpMxT8kqXkZ1YBhqzjVrBBylwaNtb22lfgz9tQosWvBn500fCQHVtLsTGXT54aHgoPtWbPOVMqg3nWMXO+xR/zATB8k3O6BPOm/Gi95fDx0Ssh3qFNkEGKFNNTbb6zBBV7BYtx5vQ8k/ek36wiG1RWefedlOmf9MZ7WLow+7PsO8i4yB9pvNYI22+Tz/LtGUEGYJTi9THCitsmZ2ee/TH3GPmL82jgHiDCjdBFNNRnhZVcq15A2PtNsdfJn3fkWUFbaZoCxglpze4Kbu+q5YNlPX/YjRdA8/vK98bb3KwiZVGTcv1+kjUc6oky/3Zo9+Pvtnp3zbd9XQzKybQbUzjTzbj0MWmM+MVc6SnibS40TF4LaoSqM2YkNjp3Y6RuPpEguDXJpPa4e9xF4nqb0BYFY99/g2RfwOiI7TZJUV15vHVTsUASTszQSwZeDtCQNeTRwE2z2qisLYUPLhFaK7ZRhUkzmVn2zwQKYVDFA17eBiankyTjXRfuKRQhnlUXIpMP6YcIp7AS7WzYKmmFdswTHChIejUkil3v1vwkSykCjqNee6haY/vptq9otMDq1P8d7fxRMnB9gNM7TfZ9qY2YGNiu5XfFdpCiP8zRtjzvK4G24LX3UdUmRmUo/APJR9Fs+jRJjDmGg9/EmgQw1/LxVFoTn7++uPFQgCeDti9wwexPpfp3oK5jU1trJSrjnoTmdNpcC3Jwgzd8JZNEXGc8OYlxHWY/utcObfGZtwQ+CThQVvuGbd/ZR9PWb38byucjSR9dpDVk3VzvLm3JEZ1zo3hB4z66GPLV/sVf0ScTsiP1edU1UApLaGLN0ZmTwkCocEdw JFh253rP 80rl9dYkmlftEhoOsq/nHE70cHyhZMiN/4wG6ow0GNlMEJ3Yw5o0S97a5WBmFq4lFOYuC+r9FoYi7pGG95nrrYIrqbkjHY2xKkwWxTlZ1MEPU2Jbr6q1O44n79y1+TA1yczXHLVCBukAxmFJ+BQl5jy0PUec+lr5BKpbb7ckIfsKInb5rbrMF10Yv01hfaTcfUzmnFDkutVYohKbTag5PG+VyRFo8cPviFkFsluD13Am0xUbgcBD5xCvxZbUj6Yd86XefW07rlB3J4yng7PfwyGnFCN4aBuwK5UFPy+1KpNHLq+A= 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 --- mm/memcontrol.c | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c3d98ab41f1f1..38f48a45b7ae5 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 +823,23 @@ 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) { + *rcu_locked = false; + 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 +873,14 @@ 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 +943,15 @@ 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