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 02142FF8864 for ; Wed, 29 Apr 2026 07:31:32 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 63F996B008C; Wed, 29 Apr 2026 03:31:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 616F06B0092; Wed, 29 Apr 2026 03:31:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 554616B0093; Wed, 29 Apr 2026 03:31:32 -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 45E0E6B008C for ; Wed, 29 Apr 2026 03:31:32 -0400 (EDT) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id D86941A02DB for ; Wed, 29 Apr 2026 07:31:31 +0000 (UTC) X-FDA: 84710773182.01.AFC208C Received: from out-189.mta0.migadu.com (out-189.mta0.migadu.com [91.218.175.189]) by imf03.hostedemail.com (Postfix) with ESMTP id 10ACC20006 for ; Wed, 29 Apr 2026 07:31:29 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=P0oDga2E; spf=pass (imf03.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.189 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=1777447890; 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=ba1LXb+IR29BnqyJkHs6D8UuBSkwHRvSb38v34WKljk=; b=BIDpgr1FZSaysftSfoFFgzkmnuWb3XwPp+qXjUSZQ4Sb65y5uKLKMt1TFh/5OhaVhESL0w wKkfAQMHmoeG1taLKnOhy4n0zqNaq/gaXIVLZvMQjeByzrEjufEzpD9mTEFmjAG9AkkuA/ 54AZ4zvmu2Dkq8PJUUvhywEHme40HuA= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=P0oDga2E; spf=pass (imf03.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.189 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=1777447890; a=rsa-sha256; cv=none; b=XQ+0Lij9HumWhqb4ixO2VuNgP5ySfJgpyc/jsXzBYXCLX2q4LEeKVGmqa+XpbkFPTZ/8IS QEVCtsZv1cH53cCWPIIVtOvNLKSITF+KWeXFOwdUIr8+ZPDVdbrVuoKiLVvWx86vx8Z5JA 1/8/i69RixdXJt0KQxv+Fm0q84jpsP0= 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=1777447887; 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=ba1LXb+IR29BnqyJkHs6D8UuBSkwHRvSb38v34WKljk=; b=P0oDga2EeBVjBCpvBe1o82imEYp5QLXUHXJZic1IoN2Eh6SeNpSzcrcVW16/okCxYCWw17 Wt5/+k7+K5PbfkfsbZfjV9y5qLUy5+YLYNVSlfILmMTu9JoejlARkoF8a2YIdK7B98NldS 5DeHAI+clLgNOUHojxRkOyESm8PLEhs= 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 v3] mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end() Date: Wed, 29 Apr 2026 15:31:05 +0800 Message-ID: <20260429073105.44472-1-qi.zheng@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: uzmawroeko7rgwkxaj6qfd5i7bkipxdo X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 10ACC20006 X-Rspam-User: X-HE-Tag: 1777447889-448804 X-HE-Meta: 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 lKbxQgPg n9+usfK9hCSEcK4gZwM7Ly7+Zwa/kpLjnA49G/rPj+dXqePrs/NVs+bOOi6lA2QxEKUGT/etbDpvH3SPO7HYEFb51rzZA7hUcgKyn0e9Gia+hfDDj/g/yxAOiuPMIldvIxhu1/sFVChXcCWn9soTV2KnC0uLaes/Y0e8ka9QauRF4Y58PNtdlYSV8Bm/LUk+adX9McVRsyirb3cA7c6igF0Vy98+fPthM1/wIAJDAskU4Hew3e2nsJE7vLc1UuP+U7PvqPK7UGZP18zrMmd7fkGayjR5l/+f9JMlfesc0N6hVloP2QTm+bzvNAA== 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 Reviewed-by: Muchun Song --- Changes in v3: - fix -Werror=uninitialized (pointed by Sashiko) - collect Reviewed-by 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..c03d4787d4668 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 = false; + 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 = false; 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