From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 3E5D1CA40; Tue, 16 Jul 2024 15:38:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721144334; cv=none; b=lfXmAGFdpdLsot+zXqBzMwrtlkipgZNwFRwNTMy49lsQxsoqT1xdf9KoUGDOEpQiEMQknHmMMzx5aIpUYyRdF721HLmOD5DkawMPDFkR/MehqCMez3Q3hMVwAnPRrcGbG9FbslqIcv09NDBsvBkANOlNuQxl6iQAjoKSB+vlpHA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721144334; c=relaxed/simple; bh=qMptx+6qkrahFzaH6aoiD3gCEThxVchg9+m8uGHCr+I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Ywe9NY/S1yzvm44WZ3SOINvuelBxFvgWSTneCjHkGPvItsaAAbHnaOtRhvGOmG+PfIIn+bK11rAp1QI5/YH6uY0f8vRkQjaEPijGW+Ve1PWQvEuquDrnjYIAP7Ttx2k+0/miSC+cXQ+Aaf0f26BwSDowt8slr7tg8cU8oeVFwTE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=NDJ9jRCl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="NDJ9jRCl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 66203C116B1; Tue, 16 Jul 2024 15:38:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1721144333; bh=qMptx+6qkrahFzaH6aoiD3gCEThxVchg9+m8uGHCr+I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NDJ9jRCldj3+hGsT6HdOqtHumfbc5fAHrq0dBc3TSvsKgeL7P+FkgIQ0/QTgfj/gY lMWuZPj/kT6zSSOaLV0G5Vb7dVgDA+4CMAMdHNAgz9W+dgNXHG9gvoYWnHhw5FOSJl /EYxZU5vkQD52YCYMxhaSk3OnpYHFy90usPB1LOs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jan Kara , Zach OKeefe , Andrew Morton Subject: [PATCH 5.4 37/78] Revert "mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again" Date: Tue, 16 Jul 2024 17:31:09 +0200 Message-ID: <20240716152742.073597362@linuxfoundation.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240716152740.626160410@linuxfoundation.org> References: <20240716152740.626160410@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jan Kara commit 30139c702048f1097342a31302cbd3d478f50c63 upstream. Patch series "mm: Avoid possible overflows in dirty throttling". Dirty throttling logic assumes dirty limits in page units fit into 32-bits. This patch series makes sure this is true (see patch 2/2 for more details). This patch (of 2): This reverts commit 9319b647902cbd5cc884ac08a8a6d54ce111fc78. The commit is broken in several ways. Firstly, the removed (u64) cast from the multiplication will introduce a multiplication overflow on 32-bit archs if wb_thresh * bg_thresh >= 1<<32 (which is actually common - the default settings with 4GB of RAM will trigger this). Secondly, the div64_u64() is unnecessarily expensive on 32-bit archs. We have div64_ul() in case we want to be safe & cheap. Thirdly, if dirty thresholds are larger than 1<<32 pages, then dirty balancing is going to blow up in many other spectacular ways anyway so trying to fix one possible overflow is just moot. Link: https://lkml.kernel.org/r/20240621144017.30993-1-jack@suse.cz Link: https://lkml.kernel.org/r/20240621144246.11148-1-jack@suse.cz Fixes: 9319b647902c ("mm/writeback: fix possible divide-by-zero in wb_dirty_limits(), again") Signed-off-by: Jan Kara Reviewed-By: Zach O'Keefe Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/page-writeback.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1530,7 +1530,7 @@ static inline void wb_dirty_limits(struc */ dtc->wb_thresh = __wb_calc_thresh(dtc); dtc->wb_bg_thresh = dtc->thresh ? - div64_u64(dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0; + div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0; /* * In order to avoid the stacked BDI deadlock we need