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 X-Spam-Level: X-Spam-Status: No, score=-10.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6CC40C28CFB for ; Tue, 2 Mar 2021 15:57:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4A7FE61494 for ; Tue, 2 Mar 2021 15:57:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1839019AbhCBP4E (ORCPT ); Tue, 2 Mar 2021 10:56:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54572 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351206AbhCBNgn (ORCPT ); Tue, 2 Mar 2021 08:36:43 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18312C061221; Tue, 2 Mar 2021 05:24:54 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1614691254; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=wODTS94r7rT1g5V5X1sVfi31G7C1dx6AeI3koBrFuog=; b=pdbP0RvjlLwhT6MGt3O7gZlZ1Q1Vzt4kvyP2jb11vAJTSkByIgWXRKROCs34fG3dE0AwTY opU3gtVisKtnKDi9H9VaqI9P0bhcuxW+ktoNqViJTmLm/vR+nRGAu3kprbB/6g5+VBDeOZ ISR5jMmEubi9pF4n2AWS1K7EJF6nQqOZ7mmnpB1SEorJMS5eXC6YUniwsW+o9YMWNEx/Xj xPN5r8bZzOsf6A9vVjHdFrwNDVoQDh1yYdiMi7tbkNI3fa/NGcpZ+fYwM9XNXow6mIJwhV c6N2wQQqBhJ0Qe4yqQIr91zIX6QAKM27rCmbJHH1uo6HBm2Z4utmX+gBS6ubiw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1614691254; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=wODTS94r7rT1g5V5X1sVfi31G7C1dx6AeI3koBrFuog=; b=PvCf8UGzPtfD1uoD5xPlqfOPLQKMHyVSQbbcSZy98K9oXrA3licqYHQYy8osgfMblhBHAa hvqSY9FaOO6n64Aw== To: Petr Mladek Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Jeff Dike , Richard Weinberger , Anton Ivanov , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , Miquel Raynal , Vignesh Raghavendra , Kees Cook , Anton Vorontsov , Colin Cross , Tony Luck , Jason Wessel , Daniel Thompson , Douglas Anderson , Pavel Tatashin , Joel Stanley , Christophe Leroy , Jordan Niethe , Alistair Popple , Ravi Bangoria , Nicholas Piggin , Mike Rapoport , Madhavan Srinivasan , Thomas Meyer , Andy Shevchenko , Davidlohr Bueso , Oleg Nesterov , Wei Li , Michael Kelley , linuxppc-dev@lists.ozlabs.org, linux-um@lists.infradead.org, linux-hyperv@vger.kernel.org, linux-mtd@lists.infradead.org, kgdb-bugreport@lists.sourceforge.net Subject: Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator In-Reply-To: References: <20210225202438.28985-1-john.ogness@linutronix.de> <20210225202438.28985-13-john.ogness@linutronix.de> Date: Tue, 02 Mar 2021 14:20:51 +0100 Message-ID: <87lfb5pu8c.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-03-01, Petr Mladek wrote: >> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c >> index 532f22637783..5a64b24a91c2 100644 >> --- a/arch/powerpc/kernel/nvram_64.c >> +++ b/arch/powerpc/kernel/nvram_64.c >> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = { >> NULL >> }; >> >> -static void oops_to_nvram(struct kmsg_dumper *dumper, >> - enum kmsg_dump_reason reason); >> +static void oops_to_nvram(enum kmsg_dump_reason reason); >> >> static struct kmsg_dumper nvram_kmsg_dumper = { >> .dump = oops_to_nvram >> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists) >> * that we think will compress sufficiently to fit in the lnx,oops-log >> * partition. If that's too much, go back and capture uncompressed text. >> */ >> -static void oops_to_nvram(struct kmsg_dumper *dumper, >> - enum kmsg_dump_reason reason) >> +static void oops_to_nvram(enum kmsg_dump_reason reason) >> { >> struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf; >> static unsigned int oops_count = 0; >> + static struct kmsg_dump_iter iter; >> static bool panicking = false; >> static DEFINE_SPINLOCK(lock); >> unsigned long flags; >> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper, >> return; >> >> if (big_oops_buf) { >> - kmsg_dump_get_buffer(dumper, false, >> + kmsg_dump_rewind(&iter); > > It would be nice to get rid of the kmsg_dump_rewind(&iter) calls > in all callers. > > A solution might be to create the following in include/linux/kmsg_dump.h > > #define KMSG_DUMP_ITER_INIT(iter) { \ > .cur_seq = 0, \ > .next_seq = U64_MAX, \ > } > > #define DEFINE_KMSG_DUMP_ITER(iter) \ > struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter) For this caller (arch/powerpc/kernel/nvram_64.c) and for (kernel/debug/kdb/kdb_main.c), kmsg_dump_rewind() is called twice within the dumper. So rewind will still be used there. > Then we could do the following at the beginning of both > kmsg_dump_get_buffer() and kmsg_dump_get_line(): > > u64 clear_seq = latched_seq_read_nolock(&clear_seq); > > if (iter->cur_seq < clear_seq) > cur_seq = clear_seq; I suppose we need to add this part anyway, if we want to enforce that records before @clear_seq are not to be available for dumpers. > I am not completely sure about next_seq: > > + kmsg_dump_get_buffer() will set it for the next call anyway. > It reads the blocks of messages from the newest. > > + kmsg_dump_get_line() wants to read the entire buffer anyway. > But there is a small risk of an infinite loop when new messages > are printed when dumping each line. > > It might be better to avoid the infinite loop. We could do the following: > > static void check_and_set_iter(struct kmsg_dump_iter) > { > if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) { > kmsg_dump_rewind(iter); > } > > and call this at the beginning of both kmsg_dump_get_buffer() > and kmsg_dump_get_line() > > What do you think? On a technical level, it does not make any difference. It is pure cosmetic. Personally, I prefer the rewind directly before the kmsg_dump_get calls because it puts the initializer directly next to the user. As an example to illustrate my view, I prefer: for (i = 0; i < n; i++) ...; instead of: int i = 0; ... for (; i < n; i++) ...; Also, I do not really like the special use of 0/U64_MAX to identify special actions of the kmsg_dump_get functions. > Note that I do not resist on it. But it might make the API easier to > use from my POV. Since you do not resist, I will keep the API the same for v4. But I will add the @clear_seq check to the kmsg_dump_get functions. John Ogness