From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) (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 1110536F437 for ; Wed, 11 Mar 2026 01:01:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773190882; cv=none; b=B4APd1nI0hcnmlV0QC6jQ3M0cM5uKlQsXADKRpGvjT2k9mkoMbYQsWO69yfodqz2kqyAYDi1Xf0K30PsZy6GUQxfCrVPfPGszNUAbt/C4VV5t/XRN8gb7MRUSnyUlyYB3bRur5iRQ8Rp029Jnput/hMi6IBlxy3M6WNCS/PF+Qc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773190882; c=relaxed/simple; bh=6uaML4bIG5BQHwy/29qZ13YY5ETzZT2ziuriWoIfeTY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=F+Re9Xjfvddypf+oImjdkKptEiivIsCtdpbgW1axQFCJyViE8nLDmDdwvNhCP4vcidY6evuCUyvV4XoF/zvIrR0KABS43akMpO0NBVPS/COEtvkV0G7Wfwcep/7EaPUwVWtpJEYAXjFbgFvBk6/OxhJRFxwYq/ZQvIwH3yTvFU8= 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=TAdFKhz4; arc=none smtp.client-ip=91.218.175.172 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="TAdFKhz4" 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=1773190878; 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=K9HsfOrfS+eqleG7h8cZbUZvSAAorR+E1jNWHkvLrQs=; b=TAdFKhz4AGLvyBz1IQjH0d3LhD1RTXPiZ2TQ7EZzlcgkFQvEF434gIsHRJvYntgR8tsGMw /waxpyhhsTwNuPUNoJhbqy1ptgdIJ350DJKpO8K6NcG2plAibuoiWLvOwomc2307tPzKWU F6v7NInwpaK1M5+TnPFoRUzVIuHdlwo= From: Shakeel Butt To: Tejun Heo Cc: Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Chen Ridong , Jakub Kicinski , Meta kernel team , linux-mm@kvack.org, netdev@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 3/3] cgroup: replace global cgroup_file_kn_lock with per-cgroup_file lock Date: Tue, 10 Mar 2026 18:01:01 -0700 Message-ID: <20260311010101.3306366-4-shakeel.butt@linux.dev> In-Reply-To: <20260311010101.3306366-1-shakeel.butt@linux.dev> References: <20260311010101.3306366-1-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: 8bit X-Migadu-Flow: FLOW_OUT Replace the global cgroup_file_kn_lock with a per-cgroup_file spinlock to eliminate cross-cgroup contention as it is not really protecting data shared between different cgroups. The lock is initialized in cgroup_add_file() alongside timer_setup(). No lock acquisition is needed during initialization since the cgroup directory is being populated under cgroup_mutex and no concurrent accessors exist at that point. Reported-by: Jakub Kicinski Signed-off-by: Shakeel Butt --- Changes since v1: - N/A include/linux/cgroup-defs.h | 1 + kernel/cgroup/cgroup.c | 24 ++++++++---------------- 2 files changed, 9 insertions(+), 16 deletions(-) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index bb92f5c169ca..ba26b5d05ce3 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -167,6 +167,7 @@ struct cgroup_file { struct kernfs_node *kn; unsigned long notified_at; struct timer_list notify_timer; + spinlock_t lock; }; /* diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index b00f4c3242e0..d899bb2aef2f 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -107,12 +107,6 @@ static bool cgroup_debug __read_mostly; */ static DEFINE_SPINLOCK(cgroup_idr_lock); -/* - * Protects cgroup_file->kn for !self csses. It synchronizes notifications - * against file removal/re-creation across css hiding. - */ -static DEFINE_SPINLOCK(cgroup_file_kn_lock); - DEFINE_PERCPU_RWSEM(cgroup_threadgroup_rwsem); #define cgroup_assert_mutex_or_rcu_locked() \ @@ -1748,9 +1742,9 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft) struct cgroup_subsys_state *css = cgroup_css(cgrp, cft->ss); struct cgroup_file *cfile = (void *)css + cft->file_offset; - spin_lock_irq(&cgroup_file_kn_lock); + spin_lock_irq(&cfile->lock); WRITE_ONCE(cfile->kn, NULL); - spin_unlock_irq(&cgroup_file_kn_lock); + spin_unlock_irq(&cfile->lock); timer_delete_sync(&cfile->notify_timer); } @@ -4427,10 +4421,8 @@ static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp, struct cgroup_file *cfile = (void *)css + cft->file_offset; timer_setup(&cfile->notify_timer, cgroup_file_notify_timer, 0); - - spin_lock_irq(&cgroup_file_kn_lock); - WRITE_ONCE(cfile->kn, kn); - spin_unlock_irq(&cgroup_file_kn_lock); + spin_lock_init(&cfile->lock); + cfile->kn = kn; } return 0; @@ -4699,13 +4691,13 @@ void cgroup_file_notify(struct cgroup_file *cfile) return; } - spin_lock_irqsave(&cgroup_file_kn_lock, flags); + spin_lock_irqsave(&cfile->lock, flags); if (cfile->kn) { kn = cfile->kn; kernfs_get(kn); WRITE_ONCE(cfile->notified_at, jiffies); } - spin_unlock_irqrestore(&cgroup_file_kn_lock, flags); + spin_unlock_irqrestore(&cfile->lock, flags); if (kn) { kernfs_notify(kn); @@ -4723,10 +4715,10 @@ void cgroup_file_show(struct cgroup_file *cfile, bool show) { struct kernfs_node *kn; - spin_lock_irq(&cgroup_file_kn_lock); + spin_lock_irq(&cfile->lock); kn = cfile->kn; kernfs_get(kn); - spin_unlock_irq(&cgroup_file_kn_lock); + spin_unlock_irq(&cfile->lock); if (kn) kernfs_show(kn, show); -- 2.52.0