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=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 BBF36C43381 for ; Tue, 19 Feb 2019 23:39:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 771822147A for ; Tue, 19 Feb 2019 23:39:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amarulasolutions.com header.i=@amarulasolutions.com header.b="WreWninV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729876AbfBSXjg (ORCPT ); Tue, 19 Feb 2019 18:39:36 -0500 Received: from mail-wr1-f66.google.com ([209.85.221.66]:45996 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728787AbfBSXjf (ORCPT ); Tue, 19 Feb 2019 18:39:35 -0500 Received: by mail-wr1-f66.google.com with SMTP id w17so23835588wrn.12 for ; Tue, 19 Feb 2019 15:39:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amarulasolutions.com; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=saahwx25cNTC84d6ArNl8JcwQIssCDuZhzTfhHa6Z/c=; b=WreWninVtedI49gXBVI7c4m3pw6FBKaBLJroDRo2yMgjI+xpEDTTBPxaXC4BC8pshn JqSYC9TnU86m+GIj8s+UsfKpmpCV+B8ZegnNEYFdStpH1czIVMaPp1JEag2H/UudlI/d wxuLk4P23AaPDCS8fycX5L7KQjd9GezIC/I8I= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=saahwx25cNTC84d6ArNl8JcwQIssCDuZhzTfhHa6Z/c=; b=gBgz+YPdr/6Zp/Jof8NE70jZJlS4E4ixH6kWh0+OQ0TGqz+omytVCK48Cf/AM14qVm zeH0XmRB8kdxXvJ8AX7TApFgosm9vmarTpw4TBTW5uGm20draCUDJJRtM1couSnG/0Zy 5ub7hz7QJI23kTbobylk/HiN646+C5JdTtmfjKGR8fGjLP46+AlJlQ1fmt1Cd03LZA+c Iz96z8h+AE5uExgMCm3RuUiwcefUuvV/ABd4+NRHyJiRPyaqxc9T0woaTXZ1yT9EVTcE Ft6bm7dhNhdyWHonncEJqnIKxqnbHAveNgvJhjC3mmKEFfA8kjnhNTB99ARe8rrqWBft SNIA== X-Gm-Message-State: AHQUAub8QF048m5qQG9epG9JWDbjKws0mqAKqOjgBSspms+6oaiZew/O TaT/oPmml01fzAS99lbgk4Kl8g== X-Google-Smtp-Source: AHgI3IZH4jvKMeEu3ALoN2V8+wD0ZFY5Rlah7Tr4GGR60A1ybdDHK8NRxqCWWBG2rHKQdq4oXW9PDg== X-Received: by 2002:a5d:6209:: with SMTP id y9mr4896033wru.140.1550619572028; Tue, 19 Feb 2019 15:39:32 -0800 (PST) Received: from andrea ([89.22.71.151]) by smtp.gmail.com with ESMTPSA id h137sm7064072wmg.41.2019.02.19.15.39.30 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 19 Feb 2019 15:39:31 -0800 (PST) Date: Wed, 20 Feb 2019 00:39:25 +0100 From: Andrea Parri To: Petr Mladek Cc: Michael Ellerman , linuxppc-dev@ozlabs.org, akpm@linux-foundation.org, tj@kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, dyoung@redhat.com, sergey.senozhatsky@gmail.com, Steven Rostedt Subject: Re: [PATCH v3 1/7] dump_stack: Support adding to the dump stack arch description Message-ID: <20190219233925.GA5648@andrea> References: <20190207124635.3885-1-mpe@ellerman.id.au> <20190211125035.GA1562@andrea> <20190211143859.dd2lkccxod3f2fwn@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190211143859.dd2lkccxod3f2fwn@pathway.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 11, 2019 at 03:38:59PM +0100, Petr Mladek wrote: > On Mon 2019-02-11 13:50:35, Andrea Parri wrote: > > Hi Michael, > > > > > > On Thu, Feb 07, 2019 at 11:46:29PM +1100, Michael Ellerman wrote: > > > Arch code can set a "dump stack arch description string" which is > > > displayed with oops output to describe the hardware platform. > > > > > > It is useful to initialise this as early as possible, so that an early > > > oops will have the hardware description. > > > > > > However in practice we discover the hardware platform in stages, so it > > > would be useful to be able to incrementally fill in the hardware > > > description as we discover it. > > > > > > This patch adds that ability, by creating dump_stack_add_arch_desc(). > > > > > > If there is no existing string it behaves exactly like > > > dump_stack_set_arch_desc(). However if there is an existing string it > > > appends to it, with a leading space. > > > > > > This makes it easy to call it multiple times from different parts of the > > > code and get a reasonable looking result. > > > > > > Signed-off-by: Michael Ellerman > > > --- > > > include/linux/printk.h | 5 ++++ > > > lib/dump_stack.c | 58 ++++++++++++++++++++++++++++++++++++++++++ > > > 2 files changed, 63 insertions(+) > > > > > > v3: No change, just widened Cc list. > > > > > > v2: Add a smp_wmb() and comment. > > > > > > v1 is here for reference https://lore.kernel.org/lkml/1430824337-15339-1-git-send-email-mpe@ellerman.id.au/ > > > > > > I'll take this series via the powerpc tree if no one minds? > > > > > > > > > diff --git a/include/linux/printk.h b/include/linux/printk.h > > > index 77740a506ebb..d5fb4f960271 100644 > > > --- a/include/linux/printk.h > > > +++ b/include/linux/printk.h > > > @@ -198,6 +198,7 @@ u32 log_buf_len_get(void); > > > void log_buf_vmcoreinfo_setup(void); > > > void __init setup_log_buf(int early); > > > __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...); > > > +__printf(1, 2) void dump_stack_add_arch_desc(const char *fmt, ...); > > > void dump_stack_print_info(const char *log_lvl); > > > void show_regs_print_info(const char *log_lvl); > > > extern asmlinkage void dump_stack(void) __cold; > > > @@ -256,6 +257,10 @@ static inline __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...) > > > { > > > } > > > > > > +static inline __printf(1, 2) void dump_stack_add_arch_desc(const char *fmt, ...) > > > +{ > > > +} > > > + > > > static inline void dump_stack_print_info(const char *log_lvl) > > > { > > > } > > > diff --git a/lib/dump_stack.c b/lib/dump_stack.c > > > index 5cff72f18c4a..69b710ff92b5 100644 > > > --- a/lib/dump_stack.c > > > +++ b/lib/dump_stack.c > > > @@ -35,6 +35,64 @@ void __init dump_stack_set_arch_desc(const char *fmt, ...) > > > va_end(args); > > > } > > > > > > +/** > > > + * dump_stack_add_arch_desc - add arch-specific info to show with task dumps > > > + * @fmt: printf-style format string > > > + * @...: arguments for the format string > > > + * > > > + * See dump_stack_set_arch_desc() for why you'd want to use this. > > > + * > > > + * This version adds to any existing string already created with either > > > + * dump_stack_set_arch_desc() or dump_stack_add_arch_desc(). If there is an > > > + * existing string a space will be prepended to the passed string. > > > + */ > > > +void __init dump_stack_add_arch_desc(const char *fmt, ...) > > > +{ > > > + va_list args; > > > + int pos, len; > > > + char *p; > > > + > > > + /* > > > + * If there's an existing string we snprintf() past the end of it, and > > > + * then turn the terminating NULL of the existing string into a space > > > + * to create one string separated by a space. > > > + * > > > + * If there's no existing string we just snprintf() to the buffer, like > > > + * dump_stack_set_arch_desc(), but without calling it because we'd need > > > + * a varargs version. > > > + */ > > > + len = strnlen(dump_stack_arch_desc_str, sizeof(dump_stack_arch_desc_str)); > > > + pos = len; > > > + > > > + if (len) > > > + pos++; > > > + > > > + if (pos >= sizeof(dump_stack_arch_desc_str)) > > > + return; /* Ran out of space */ > > > + > > > + p = &dump_stack_arch_desc_str[pos]; > > > + > > > + va_start(args, fmt); > > > + vsnprintf(p, sizeof(dump_stack_arch_desc_str) - pos, fmt, args); > > > + va_end(args); > > > + > > > + if (len) { > > > + /* > > > + * Order the stores above in vsnprintf() vs the store of the > > > + * space below which joins the two strings. Note this doesn't > > > + * make the code truly race free because there is no barrier on > > > + * the read side. ie. Another CPU might load the uninitialised > > > + * tail of the buffer first and then the space below (rather > > > + * than the NULL that was there previously), and so print the > > > + * uninitialised tail. But the whole string lives in BSS so in > > > + * practice it should just see NULLs. > > > > The comment doesn't say _why_ we need to order these stores: IOW, what > > will or can go wrong without this order? This isn't clear to me. > > > > Another good practice when adding smp_*-constructs (as discussed, e.g., > > at KS'18) is to indicate the matching construct/synch. mechanism. > > Yes, one barrier without a counter-part is suspicious. As is this silence..., Michael, what happened to this patch? did you submit a new version? > > If the parallel access is really needed then we could define the > current length as atomic_t and use: > > + atomic_cmpxchg() to reserve the space for the string > + %*s to limit the printed length > > In the worst case, we would print an incomplete string. > See below for a sample code. Seems worth exploring, IMO; but I'd like to first hear _clear about the _intended semantics (before digging into alternatives)... +rostedt, who first raised the question about "parallel accesses" http://lkml.kernel.org/r/20190208185515.r6vkrezbd3odhpxt@home.goodmis.org Andrea > > > BTW: There are very few users of dump_stack_set_arch_desc(). > I would use dump_stack_add_arch_desc() everywhere to keep > it simple and have a reasonable semantic. > > > This is what I mean (only compile tested): > > diff --git a/lib/dump_stack.c b/lib/dump_stack.c > index 5cff72f18c4a..311dd20cc6a7 100644 > --- a/lib/dump_stack.c > +++ b/lib/dump_stack.c > @@ -14,9 +14,10 @@ > #include > > static char dump_stack_arch_desc_str[128]; > +static atomic_t arch_desc_str_len; > > /** > - * dump_stack_set_arch_desc - set arch-specific str to show with task dumps > + * dump_stack_set_arch_desc - add arch-specific str to show with task dumps > * @fmt: printf-style format string > * @...: arguments for the format string > * > @@ -25,13 +26,32 @@ static char dump_stack_arch_desc_str[128]; > * arch wants to make use of such an ID string, it should initialize this > * as soon as possible during boot. > */ > -void __init dump_stack_set_arch_desc(const char *fmt, ...) > +void __init dump_stack_add_arch_desc(const char *fmt, ...) > { > - va_list args; > + va_list args, args2; > + int len, cur_len, old_len; > > va_start(args, fmt); > - vsnprintf(dump_stack_arch_desc_str, sizeof(dump_stack_arch_desc_str), > + > + va_copy(args2, args); > + len = vsnprintf(NULL, sizeof(dump_stack_arch_desc_str), > + fmt, args2); > + va_end(args2); > + > +try_again: > + cur_len = atomic_read(&arch_desc_str_len); > + if (cur_len + len > sizeof(dump_stack_arch_desc_str)) > + goto out; > + > + old_len = atomic_cmpxchg(&arch_desc_str_len, > + cur_len, cur_len + len); > + if (old_len != cur_len) > + goto try_again; > + > + vsnprintf(dump_stack_arch_desc_str + old_len, > + sizeof(dump_stack_arch_desc_str) - old_len, > fmt, args); > +out: > va_end(args); > } > > @@ -44,6 +64,8 @@ void __init dump_stack_set_arch_desc(const char *fmt, ...) > */ > void dump_stack_print_info(const char *log_lvl) > { > + int len; > + > printk("%sCPU: %d PID: %d Comm: %.20s %s%s %s %.*s\n", > log_lvl, raw_smp_processor_id(), current->pid, current->comm, > kexec_crash_loaded() ? "Kdump: loaded " : "", > @@ -52,9 +74,11 @@ void dump_stack_print_info(const char *log_lvl) > (int)strcspn(init_utsname()->version, " "), > init_utsname()->version); > > - if (dump_stack_arch_desc_str[0] != '\0') > - printk("%sHardware name: %s\n", > - log_lvl, dump_stack_arch_desc_str); > + len = atomic_read(&arch_desc_str_len); > + if (len) { > + printk("%sHardware name: %*s\n", > + log_lvl, len, dump_stack_arch_desc_str); > + } > > print_worker_info(log_lvl, current); > } > > Best Regards, > Petr