From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 375BF3EBF27 for ; Sat, 28 Feb 2026 14:20:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772288451; cv=none; b=DDNTvW75N8WTObwruBVm6C36wi2k7DffWz2gSh/HPCFbkuFfzdhhbutPfs5BVwDRs+0s6G2Bqi4YgN2911W0UNnGta8TlfeYXnxQR94OrCoDq6Zg5uQp97uicHZ//atSAMu93oIKCxEgSQwmamJyovx48eEKdvsohA/7LY3vW4I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772288451; c=relaxed/simple; bh=Nt/BUPJSvd9WEDeocpmWi6aZzL7kRdJmd8JiUYGr7OA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kiY+o4qVOdlg5nlRX/C6k33OWsigIcmn/dn0hNuUJpDl3mCAbzcOdyUKdBb3mUAW6aZVvfM3b/AgqyIof/nzwIXHmUupuVGeDanIQHSfN1YPD7jEPSHjfECJayMkcwNBoTPyeYXbPFEYH31Ggk2mM7/Jvik7ks9IOguOHlqwpgE= 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=JcI/7Imt; arc=none smtp.client-ip=91.218.175.188 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="JcI/7Imt" 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=1772288448; 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=Cngsu4QC/s/LsygBwa0X1EgXCc0toiqGLgWGzEjWZ30=; b=JcI/7ImtJYPNViw4hRAStRxiuwGD/K2BPN2nAe3Qmvd6t5RC1XpXCbi6w+EM62Bo875+l4 5tDwOAflDGo6MkCtOuMzbje/vhPK9w/h+fiw6v7rup3BxR94zCBkD1jBGwdz45EHLE8ITp x150gwG5DGtZHS+kNuAC8Jjzi8/vgj4= From: Shakeel Butt To: Tejun Heo Cc: Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Roman Gushchin , Kuniyuki Iwashima , Daniel Sedlak , Meta kernel team , linux-mm@kvack.org, netdev@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Jakub Kicinski Subject: [PATCH 3/3] cgroup: replace global cgroup_file_kn_lock with per-cgroup_file lock Date: Sat, 28 Feb 2026 06:20:18 -0800 Message-ID: <20260228142018.3178529-4-shakeel.butt@linux.dev> In-Reply-To: <20260228142018.3178529-1-shakeel.butt@linux.dev> References: <20260228142018.3178529-1-shakeel.butt@linux.dev> Precedence: bulk X-Mailing-List: netdev@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. Signed-off-by: Shakeel Butt Reported-by: Jakub Kicinski --- 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 5473ebd0f6c1..b502acad3c5c 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); } @@ -4428,10 +4422,8 @@ 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; @@ -4696,7 +4688,7 @@ void cgroup_file_notify(struct cgroup_file *cfile) if (time_before_eq(jiffies, last + CGROUP_FILE_NOTIFY_MIN_INTV)) return; - spin_lock_irqsave(&cgroup_file_kn_lock, flags); + spin_lock_irqsave(&cfile->lock, flags); if (cfile->kn) { last = cfile->notified_at; next = last + CGROUP_FILE_NOTIFY_MIN_INTV; @@ -4709,7 +4701,7 @@ void cgroup_file_notify(struct cgroup_file *cfile) 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); @@ -4727,10 +4719,10 @@ 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); -- 2.47.3