From nobody Thu Dec 18 07:13:15 2025 Received: from out-170.mta1.migadu.com (out-170.mta1.migadu.com [95.215.58.170]) (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 976BD18CBEC for ; Fri, 14 Mar 2025 06:15:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741932948; cv=none; b=BMmhyrmZyf5NkxikUzU59rXIA6ORBZl1lUzUJ6ftn0USkHA3E1aG5AFCRJt+G6iH3XZqKlHgfI8I/PWOD/thqJeIAz01dxuB+U00KLMqypkuQgbpGmwmujlkMa7xZHRWtDATw3XenONuulKUvvvRQrHDiSsaLEtNDVeeSImp614= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741932948; c=relaxed/simple; bh=LloJnKkIR/QdFvsz1WTvP10su9GsOgJ3e0RXRBD9G0s=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tE1LwWZbkfEAqmyJzLo7RdRwrs2yusVGXtRQEiL5PaYXzrk2E2T4oR2ezlOV/QGH1IibTYjVB5Qj36k01M0qMXz1TT78rAjSpf7Nj7PWismyW4/A/cVtiqFHpRlVuYBhaQW6sS5J7Cqr6lkv0Ib0t2ikbpHDH8sGb6vdi4aBDnI= 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=V274faEo; arc=none smtp.client-ip=95.215.58.170 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="V274faEo" 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=1741932944; 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: in-reply-to:in-reply-to:references:references; bh=tHvct7NUO2otKVtcPkikbwH9IxeqmMsC6tyfV+hMsCI=; b=V274faEovU31wH6hmPF8Pl1ql5SCdkECGFNsM9aIg8fqkshlyZQjJkHlOiibZ5eK8EBIaF mzT2xavCrHmwrG2e71ysA2lRB0K2dCx5x92LDIJjzGPXTyyBhrFDUktB4v80nkwy47GVhp OIu/u1LFsSewxNzC4GuEWlmMp1zITI8= From: Shakeel Butt To: Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Vlastimil Babka , Sebastian Andrzej Siewior , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: [RFC PATCH 06/10] memcg: do obj_cgroup_put inside drain_obj_stock Date: Thu, 13 Mar 2025 23:15:07 -0700 Message-ID: <20250314061511.1308152-7-shakeel.butt@linux.dev> In-Reply-To: <20250314061511.1308152-1-shakeel.butt@linux.dev> References: <20250314061511.1308152-1-shakeel.butt@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: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" Previously we could not call obj_cgroup_put() inside the local lock because on the put on the last reference, the release function obj_cgroup_release() may try to re-acquire the local lock. However that chain has been broken. Now simply do obj_cgroup_put() inside drain_obj_stock() instead of returning the old objcg. Signed-off-by: Shakeel Butt --- mm/memcontrol.c | 37 +++++++++++-------------------------- 1 file changed, 11 insertions(+), 26 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 83db180455a1..3c4de384b5a0 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1778,7 +1778,7 @@ static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_s= tock) =3D { }; static DEFINE_MUTEX(percpu_charge_mutex); =20 -static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock); +static void drain_obj_stock(struct memcg_stock_pcp *stock); static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, struct mem_cgroup *root_memcg); =20 @@ -1853,7 +1853,6 @@ static void drain_stock(struct memcg_stock_pcp *stock) static void drain_local_stock(struct work_struct *dummy) { struct memcg_stock_pcp *stock; - struct obj_cgroup *old =3D NULL; unsigned long flags; =20 /* @@ -1864,12 +1863,11 @@ static void drain_local_stock(struct work_struct *d= ummy) localtry_lock_irqsave(&memcg_stock.stock_lock, flags); =20 stock =3D this_cpu_ptr(&memcg_stock); - old =3D drain_obj_stock(stock); + drain_obj_stock(stock); drain_stock(stock); clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); =20 localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags); - obj_cgroup_put(old); } =20 /* Should never be called with root_mem_cgroup. */ @@ -1951,18 +1949,16 @@ void drain_all_stock(struct mem_cgroup *root_memcg) static int memcg_hotplug_cpu_dead(unsigned int cpu) { struct memcg_stock_pcp *stock; - struct obj_cgroup *old; unsigned long flags; =20 stock =3D &per_cpu(memcg_stock, cpu); =20 /* drain_obj_stock requires stock_lock */ localtry_lock_irqsave(&memcg_stock.stock_lock, flags); - old =3D drain_obj_stock(stock); + drain_obj_stock(stock); localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags); =20 drain_stock(stock); - obj_cgroup_put(old); =20 return 0; } @@ -2745,24 +2741,20 @@ void __memcg_kmem_uncharge_page(struct page *page, = int order) } =20 /* Replace the stock objcg with objcg, return the old objcg */ -static struct obj_cgroup *replace_stock_objcg(struct memcg_stock_pcp *stoc= k, - struct obj_cgroup *objcg) +static void replace_stock_objcg(struct memcg_stock_pcp *stock, + struct obj_cgroup *objcg) { - struct obj_cgroup *old =3D NULL; - - old =3D drain_obj_stock(stock); + drain_obj_stock(stock); obj_cgroup_get(objcg); stock->nr_bytes =3D atomic_read(&objcg->nr_charged_bytes) ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; WRITE_ONCE(stock->cached_objcg, objcg); - return old; } =20 static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *= pgdat, enum node_stat_item idx, int nr) { struct memcg_stock_pcp *stock; - struct obj_cgroup *old =3D NULL; unsigned long flags; int *bytes; =20 @@ -2775,7 +2767,7 @@ static void mod_objcg_state(struct obj_cgroup *objcg,= struct pglist_data *pgdat, * changes. */ if (READ_ONCE(stock->cached_objcg) !=3D objcg) { - old =3D replace_stock_objcg(stock, objcg); + replace_stock_objcg(stock, objcg); stock->cached_pgdat =3D pgdat; } else if (stock->cached_pgdat !=3D pgdat) { /* Flush the existing cached vmstat data */ @@ -2816,7 +2808,6 @@ static void mod_objcg_state(struct obj_cgroup *objcg,= struct pglist_data *pgdat, __mod_objcg_mlstate(objcg, pgdat, idx, nr); =20 localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags); - obj_cgroup_put(old); } =20 static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_by= tes) @@ -2838,12 +2829,12 @@ static bool consume_obj_stock(struct obj_cgroup *ob= jcg, unsigned int nr_bytes) return ret; } =20 -static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock) +static void drain_obj_stock(struct memcg_stock_pcp *stock) { struct obj_cgroup *old =3D READ_ONCE(stock->cached_objcg); =20 if (!old) - return NULL; + return; =20 if (stock->nr_bytes) { unsigned int nr_pages =3D stock->nr_bytes >> PAGE_SHIFT; @@ -2896,11 +2887,7 @@ static struct obj_cgroup *drain_obj_stock(struct mem= cg_stock_pcp *stock) } =20 WRITE_ONCE(stock->cached_objcg, NULL); - /* - * The `old' objects needs to be released by the caller via - * obj_cgroup_put() outside of memcg_stock_pcp::stock_lock. - */ - return old; + obj_cgroup_put(old); } =20 static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, @@ -2922,7 +2909,6 @@ static void refill_obj_stock(struct obj_cgroup *objcg= , unsigned int nr_bytes, bool allow_uncharge) { struct memcg_stock_pcp *stock; - struct obj_cgroup *old =3D NULL; unsigned long flags; unsigned int nr_pages =3D 0; =20 @@ -2930,7 +2916,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg= , unsigned int nr_bytes, =20 stock =3D this_cpu_ptr(&memcg_stock); if (READ_ONCE(stock->cached_objcg) !=3D objcg) { /* reset if necessary */ - old =3D replace_stock_objcg(stock, objcg); + replace_stock_objcg(stock, objcg); allow_uncharge =3D true; /* Allow uncharge when objcg changes */ } stock->nr_bytes +=3D nr_bytes; @@ -2941,7 +2927,6 @@ static void refill_obj_stock(struct obj_cgroup *objcg= , unsigned int nr_bytes, } =20 localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags); - obj_cgroup_put(old); =20 if (nr_pages) obj_cgroup_uncharge_pages(objcg, nr_pages); --=20 2.47.1