From nobody Mon Feb 9 17:23:05 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 F20431E5708; Thu, 30 Jan 2025 14:02:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738245745; cv=none; b=p7a8foP7+BlaVVw9mQ2pgI14p+CDOkjnX8EsflAZ+sVXVnatfxFVpZxLByVrocr9skq71YXAQDTkX7HkuWjba1TY3sRAK3Wo2X36OGTokfTosK8iIEtHofRXiUU/UVv8IzUsqh1SbScDLQdGAY7RSsIdxjF+9U1jWbWQAZgBGCU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738245745; c=relaxed/simple; bh=tR45VY94czRZPH94WmhYPOQ1mLEIOTHPhxsX88grZxc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=U5Az2P5uvMHz6549XDi2XC8B3zaoDR761QsR/vrx0/WEPRUk7BqqrHyXZlJKrxzozvJjUk3BQsJfgwSAN1qhbE7HGLdX3LZaBWgfXp2GLwCMhJNvFB/mntGBL8fLlT8038jy3blDWWQtKk8qNYSaoWpSgLxLbxBCFA0CliuUmrA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=4zRZPAtI; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ML2h1YCO; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="4zRZPAtI"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ML2h1YCO" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1738245742; 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=jHJX6bEa0XtyQR0u+s3KZKeiU8ZuhShX3XwcYletJb0=; b=4zRZPAtIeO/x9K1DBs5KAd3WjZJpPtk0HIOubjPy8m7LuABXg8vveFTPogzknIrSRlpJSf q4R7le1MIEwlTJ+ETnVlN/YR8AHGeeXQ51guLWYKVz5qkMUnfm9mqIxvLe/JrsBZdT+V9G yt6YwBcMnbC1eMGqNSkGa6C3Q0LhUoGFOnBY/N5YO+zOqW+Plak+qgRs9DdO9kLnLOoW1q ri3HpeRRthLvXN0EXiPZPsKvsqNqbNYJG6YSTlwa2aPj7s16Pm64QJYXiDxHiGdm8QYpWq qWNmvWqyOpOh2OSMIgZY5FIow43fC6/YjzUEaAK65FJTamG9BnB7078NRSakNw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1738245742; 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=jHJX6bEa0XtyQR0u+s3KZKeiU8ZuhShX3XwcYletJb0=; b=ML2h1YCOl7yzvYuj3oEcDEJu6ZGrbjpb+uUyIdWu5CUaxxdYTJf90Edb674sPSL6C4BmLL ZRfym3wHCZHC7OCA== To: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Michal=20Koutn=C3=BD?= , "Paul E. McKenney" , Boqun Feng , Greg Kroah-Hartman , Hillf Danton , Johannes Weiner , Marco Elver , Tejun Heo , tglx@linutronix.de, Sebastian Andrzej Siewior Subject: [PATCH v6 4/6] kernfs: Don't re-lock kernfs_root::kernfs_rwsem in kernfs_fop_readdir(). Date: Thu, 30 Jan 2025 15:02:05 +0100 Message-ID: <20250130140207.1914339-5-bigeasy@linutronix.de> In-Reply-To: <20250130140207.1914339-1-bigeasy@linutronix.de> References: <20250130140207.1914339-1-bigeasy@linutronix.de> 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 Content-Type: text/plain; charset="utf-8" The readdir operation iterates over all entries and invokes dir_emit() for every entry passing kernfs_node::name as argument. Since the name argument can change, and become invalid, the kernfs_root::kernfs_rwsem lock should not be dropped to prevent renames during the operation. The lock drop around dir_emit() has been initially introduced in commit 1e5289c97bba2 ("sysfs: Cache the last sysfs_dirent to improve readdir sc= alability v2") to avoid holding a global lock during a page fault. The lock drop is wrong since the support of renames and not a big burden since the lock is no longer global. Don't re-acquire kernfs_root::kernfs_rwsem while copying the name to the userpace buffer. Acked-by: Tejun Heo Signed-off-by: Sebastian Andrzej Siewior --- fs/kernfs/dir.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 458519e416fe7..5a1fea414996e 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1868,10 +1868,10 @@ static int kernfs_fop_readdir(struct file *file, st= ruct dir_context *ctx) file->private_data =3D pos; kernfs_get(pos); =20 - up_read(&root->kernfs_rwsem); - if (!dir_emit(ctx, name, len, ino, type)) + if (!dir_emit(ctx, name, len, ino, type)) { + up_read(&root->kernfs_rwsem); return 0; - down_read(&root->kernfs_rwsem); + } } up_read(&root->kernfs_rwsem); file->private_data =3D NULL; --=20 2.47.2