From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7A592346E7F for ; Tue, 28 Apr 2026 03:07:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777345645; cv=none; b=u/Ct8HPSsva4Y5LuzmW3uEDCZ328sozzIVIGv467YFNeSFg3lUoZtOj1TLrlKwFeVEWxQyFcAHtYexeobF5pF3Lm7jana6feICfiFfdX6y0CCNdRLOJzaKuhnfKj3dMK35POLhxa/iHXofh3URjMIHrt/0R5HIFBE4kYlu8zquw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777345645; c=relaxed/simple; bh=5nslgPB9Y8X7FRFmFPOskniWXDHRHVAjP7pSlal177o=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Dw/BQ2WZ49WSzeZawnX7i4RBQdQxkCzBNbMPSqUukLOyiSpm2YVNvqVJ6sZ4z2nyUlQVyn2gyz51TT2QhvCBACc/8eiHVoZr+Lh/aFAKmmklAbtsWR1+RzNwicRtnAz++ZtntZ2cRRaOazyGmjLqOaCKUpo+mj3WmZAAilwcRB8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=R5+J33wq; arc=none smtp.client-ip=95.215.58.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="R5+J33wq" 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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