From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 E0663329E49 for ; Wed, 29 Apr 2026 10:46:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777459599; cv=none; b=nMriSRE6JsoVKE/oeVrgvksxoicJhMRef82SbkBwuDm0sS4z52t4rG7dG9mud4t0xan2fJdfs8uR7D+CNRGYpFiygtT7iwfQSTHYYlx2dSYfR1Ws7jRTckxBEd0l8HnnhNkaMteN605/T5XFHA1JDiJKbTXiiDj+sR3qq6fPGno= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777459599; c=relaxed/simple; bh=Zf1epmDk6wj/6TQEaIpJ0yMoljkq//9XCTsczO6fZm0=; h=Date:To:From:Subject:Message-Id; b=beluEfROR1UucE9k+LKgLIoxjnKl4IkzV1NKp2jTPA1Ss+pS+PNM8+v+9Jvw9QUX5+29FX5XRd+ziPCpVPr5By3p75lpHdLiX6dfGjZG0r37cp3GOTT/6wN/SY+W62wRx2tVB2APoAXRH7XjtoRHv6w5rWVi35+SoOcfFBeZl04= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=ccgOpASL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="ccgOpASL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7D35EC19425; Wed, 29 Apr 2026 10:46:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1777459598; bh=Zf1epmDk6wj/6TQEaIpJ0yMoljkq//9XCTsczO6fZm0=; h=Date:To:From:Subject:From; b=ccgOpASLwDvnaepMALDMir7sGXwybHLeyAphiBp9+R8SNTr+2iuekpUUOqtY+7znu ejlQxqu636m+pa/Ca5MPuTtMob5COa2M4KhJdEFXz1qiBeK2eTBSLDk1iSsYdxa44r 06pVH2yK+Yt5c9q47YZpbOnWSXeL1BBJnceh18GA= Date: Wed, 29 Apr 2026 03:46:37 -0700 To: mm-commits@vger.kernel.org,shakeel.butt@linux.dev,roman.gushchin@linux.dev,muchun.song@linux.dev,mhocko@kernel.org,hannes@cmpxchg.org,zhengqi.arch@bytedance.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch added to mm-hotfixes-unstable branch Message-Id: <20260429104638.7D35EC19425@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Qi Zheng Subject: mm: memcontrol: fix rcu unbalance in get_non_dying_memcg_end() Date: Wed, 29 Apr 2026 15:31:05 +0800 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. Link: https://lore.kernel.org/20260429073105.44472-1-qi.zheng@linux.dev Fixes: 8285917d6f38 ("mm: memcontrol: prepare for reparenting non-hierarchical stats") Signed-off-by: Qi Zheng Acked-by: Shakeel Butt Reviewed-by: Muchun Song Cc: Johannes Weiner Cc: Michal Hocko Cc: Qi Zheng Cc: Roman Gushchin Signed-off-by: Andrew Morton --- mm/memcontrol.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) --- a/mm/memcontrol.c~mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end +++ a/mm/memcontrol.c @@ -805,12 +805,17 @@ static long memcg_state_val_in_pages(int * 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 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 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(struc 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); } /** _ Patches currently in -mm which might be from zhengqi.arch@bytedance.com are mm-memcontrol-fix-rcu-unbalance-in-get_non_dying_memcg_end.patch