From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DA3AAECAAA1 for ; Thu, 27 Oct 2022 20:34:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235948AbiJ0Uev (ORCPT ); Thu, 27 Oct 2022 16:34:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233652AbiJ0Uer (ORCPT ); Thu, 27 Oct 2022 16:34:47 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 453DA32076; Thu, 27 Oct 2022 13:34:45 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 0160EB827D3; Thu, 27 Oct 2022 20:34:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E7EBAC433D7; Thu, 27 Oct 2022 20:34:39 +0000 (UTC) Date: Thu, 27 Oct 2022 16:34:53 -0400 From: Steven Rostedt To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Stephen Boyd , Guenter Roeck , Jesse Brandeburg , Tony Nguyen , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Mirko Lindner , Stephen Hemminger , Martin KaFai Lau , Alexei Starovoitov , Kuniyuki Iwashima , Pavel Begunkov , Menglong Dong , linux-usb@vger.kernel.org, linux-wireless@vger.kernel.org, bridge@lists.linux-foundation.org, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, lvs-devel@vger.kernel.org, linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org, tipc-discussion@lists.sourceforge.net Subject: Re: [RFC][PATCH v2 19/31] timers: net: Use del_timer_shutdown() before freeing timer Message-ID: <20221027163453.383bbf8e@gandalf.local.home> In-Reply-To: References: <20221027150525.753064657@goodmis.org> <20221027150928.780676863@goodmis.org> <20221027155513.60b211e2@gandalf.local.home> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 27 Oct 2022 13:15:23 -0700 Linus Torvalds wrote: > On Thu, Oct 27, 2022 at 12:55 PM Steven Rostedt wrote: > > > > I think we need to update this code to squeeze in a del_timer_shutdown() to > > make sure that the timers are never restarted. > > So the reason the networking code does this is that it can't just do > the old 'sync()' thing, the timers are deleted in contexts where that > isn't valid. > > Which is also afaik why the networking code does that whole "timer > implies a refcount to the socket" and then does the > > if (del_timer(timer)) > sock_put() > > thing (ie if the del_timer failed - possibly because it was already > running - you leave the refcount alone). OK, so the above is assuming that the timer is always active, and del_timer() returns if it successfully removed it (where it can call sock_put()), but if del_timer() returns 0, that means the timer is currently running (or about to be), so it doesn't call sock_put(). > > So the networking code cannot do the del_timer_shutdown() for the same > reason it cannot do the del_timer_sync(): it can't afford to wait for > the timer to stop running. > > I suspect it needs something like a new "del_timer_shutdown_async()" > that isn't synchronous, but does that > > - acts as del_timer in that it doesn't wait, and returns a success if > it could just remove the pending case > > - does that "mark timer for shutdown" in that success case > > or something similar. > What about del_timer_try_shutdown(), that if it removes the timer, it sets the function to NULL (making it equivalent to a successful shutdown), otherwise it does nothing. Allowing the the timer to be rearmed. I think this would work in this case. -- Steve