From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (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 C4D5235FF57 for ; Wed, 11 Mar 2026 01:01:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773190876; cv=none; b=WVAlkDaES4oi0s3wSa2YxNdlk8ImWqwQdf0tpm5t/YYDZ0R93pfZM2F8yws13+IMSz/tWmMFnC4IYW9yD/sd965CM3xrHHDtcGQAH3GDa9owJcQ1/G2ME2Eb2nAFLyD2Bao2NNtYIlA5CG0K6Iqnym9EpWlADnI0Fh+lYt1Us2Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773190876; c=relaxed/simple; bh=CeiVAzQ8H3v9HU5U+4twZa9/8jKcb88Q/jIDoZ8McoA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PTEegqa3cqs7U4tASjvR3U1baG8PofmrsSoZrS7hUhhYQtb6SLl1mgVKlghDMPti7izt8sHXuYbm+TOoXud/LE+lBt2tM6CkqOEo8UcdGDvXB+iCCX1/LEBmcRHnxdJ6yDwGzAWfg7bV4kjF92PN2d4uQPvSxu02MVgmHX3lqoY= 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=mENMEn6+; arc=none smtp.client-ip=91.218.175.174 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="mENMEn6+" 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=1773190872; 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=qk+QKL+WWCN38YTC4yYy3ziupLEe6KfdX1avXXt55Pw=; b=mENMEn6+BnsiU6XV1NWHpmL1SS60MUkAa0TYha8EuJ+HcpgFsTh3g3+yZWm2JbmUzTk60x 5ZI+gQXEPI0d31SneW9hVgYfrQqPcyApjeizbDMb/HcJg1y90MgywSWKPH3aOHmYtdIuOp KI7aT5tKCeWCb35clfum+yD1/0FaEio= 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 1/3] cgroup: reduce cgroup_file_kn_lock hold time in cgroup_file_notify() Date: Tue, 10 Mar 2026 18:00:59 -0700 Message-ID: <20260311010101.3306366-2-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 cgroup_file_notify() calls kernfs_notify() while holding the global cgroup_file_kn_lock. kernfs_notify() does non-trivial work including wake_up_interruptible() and acquisition of a second global spinlock (kernfs_notify_lock), inflating the hold time. Take a kernfs_get() reference under the lock and call kernfs_notify() after dropping it, following the pattern from cgroup_file_show(). Reported-by: Jakub Kicinski Signed-off-by: Shakeel Butt --- Changes since v1: - N/A kernel/cgroup/cgroup.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 7e99258e9090..b3fbeadb2b5a 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -4686,6 +4686,7 @@ int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) void cgroup_file_notify(struct cgroup_file *cfile) { unsigned long flags; + struct kernfs_node *kn = NULL; spin_lock_irqsave(&cgroup_file_kn_lock, flags); if (cfile->kn) { @@ -4695,11 +4696,17 @@ void cgroup_file_notify(struct cgroup_file *cfile) if (time_in_range(jiffies, last, next)) { timer_reduce(&cfile->notify_timer, next); } else { - kernfs_notify(cfile->kn); + kn = cfile->kn; + kernfs_get(kn); cfile->notified_at = jiffies; } } spin_unlock_irqrestore(&cgroup_file_kn_lock, flags); + + if (kn) { + kernfs_notify(kn); + kernfs_put(kn); + } } EXPORT_SYMBOL_GPL(cgroup_file_notify); -- 2.52.0