Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755685AbZD2Cjc (ORCPT ); Tue, 28 Apr 2009 22:39:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752036AbZD2CjX (ORCPT ); Tue, 28 Apr 2009 22:39:23 -0400 Received: from mga03.intel.com ([143.182.124.21]:34735 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750733AbZD2CjW (ORCPT ); Tue, 28 Apr 2009 22:39:22 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.40,264,1239001200"; d="scan'208";a="137066185" Date: Wed, 29 Apr 2009 10:38:42 +0800 From: Wu Fengguang To: Andrew Morton Cc: "linux-kernel@vger.kernel.org" , "kosaki.motohiro@jp.fujitsu.com" , "andi@firstfloor.org" , "mpm@selenic.com" , "adobriyan@gmail.com" , "linux-mm@kvack.org" , Stephen Rothwell , Chandra Seetharaman , Nathan Lynch , Olof Johansson , Helge Deller Subject: Re: [PATCH 5/5] proc: export more page flags in /proc/kpageflags Message-ID: <20090429023842.GA10266@localhost> References: <20090428010907.912554629@intel.com> <20090428014920.769723618@intel.com> <20090428143244.4e424d36.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090428143244.4e424d36.akpm@linux-foundation.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7415 Lines: 191 On Wed, Apr 29, 2009 at 05:32:44AM +0800, Andrew Morton wrote: > On Tue, 28 Apr 2009 09:09:12 +0800 > Wu Fengguang wrote: > > > +/* > > + * Kernel flags are exported faithfully to Linus and his fellow hackers. > > + * Otherwise some details are masked to avoid confusing the end user: > > + * - some kernel flags are completely invisible > > + * - some kernel flags are conditionally invisible on their odd usages > > + */ > > +#ifdef CONFIG_DEBUG_KERNEL > > +static inline int genuine_linus(void) { return 1; } > > Although he's a fine chap, the use of the "_linus" tag isn't terribly > clear (to me). I think what you're saying here is that this enables > kernel-developer-only features, yes? Yes. > If so, perhaps we could come up with an identifier which expresses that > more clearly. > > But I'd expect that everyone and all distros enable CONFIG_DEBUG_KERNEL > for _some_ reason, so what's the point? Good point! I can confirm my debian has CONFIG_DEBUG_KERNEL=Y! > It is preferable that we always implement the same interface for all > Kconfig settings. If this exposes information which is confusing or > not useful to end-users then so be it - we should be able to cover that > in supporting documentation. My original patch takes that straightforward manner - and I still like it. I would be very glad to move the filtering code from kernel to user space. The use of more obscure flags could be discouraged by _not_ documenting them. A really curious user is encouraged to refer to the code for the exact meaning (and perhaps become a kernel developer ;-) > Also, as mentioned in the other email, it would be good if we were to > publish a little userspace app which people can use to access this raw > data. We could give that application an `--i-am-a-kernel-developer' > option! OK. I'll include page-types.c in the next take. > > +#else > > +static inline int genuine_linus(void) { return 0; } > > +#endif > > This isn't an appropriate use of CONFIG_DEBUG_KERNEL. > > DEBUG_KERNEL is a Kconfig-only construct which is use to enable _other_ > debugging features. The way you've used it here, if the person who is > configuring the kernel wants to enable any other completely-unrelated > debug feature, they have to enable DEBUG_KERNEL first. But when they > do that, they unexpectedly alter the behaviour of pagemap! > > There are two other places where CONFIG_DEBUG_KERNEL affects code > generation in .c files: arch/parisc/mm/init.c and > arch/powerpc/kernel/sysfs.c. These are both wrong, and need slapping ;) (add cc to related maintainers) CONFIG_DEBUG_KERNEL being enabled in distro kernels effectively means #ifdef CONFIG_DEBUG_KERNEL == #if 1 as the following patch demos. Now it becomes obviously silly. diff --git a/arch/parisc/mm/init.c b/arch/parisc/mm/init.c index 4356ceb..59fb910 100644 --- a/arch/parisc/mm/init.c +++ b/arch/parisc/mm/init.c @@ -368,19 +368,19 @@ static void __init setup_bootmem(void) request_resource(&sysram_resources[0], &pdcdata_resource); } void free_initmem(void) { unsigned long addr, init_begin, init_end; printk(KERN_INFO "Freeing unused kernel memory: "); -#ifdef CONFIG_DEBUG_KERNEL +#if 1 /* Attempt to catch anyone trying to execute code here * by filling the page with BRK insns. * * If we disable interrupts for all CPUs, then IPI stops working. * Kinda breaks the global cache flushing. */ local_irq_disable(); memset(__init_begin, 0x00, @@ -519,19 +519,19 @@ void __init mem_init(void) printk(KERN_INFO "Memory: %luk/%luk available (%dk kernel code, %dk reserved, %dk data, %dk init)\n", (unsigned long)nr_free_pages() << (PAGE_SHIFT-10), num_physpages << (PAGE_SHIFT-10), codesize >> 10, reservedpages << (PAGE_SHIFT-10), datasize >> 10, initsize >> 10 ); -#ifdef CONFIG_DEBUG_KERNEL /* double-sanity-check paranoia */ +#if 1 /* double-sanity-check paranoia */ printk("virtual kernel memory layout:\n" " vmalloc : 0x%p - 0x%p (%4ld MB)\n" " memory : 0x%p - 0x%p (%4ld MB)\n" " .init : 0x%p - 0x%p (%4ld kB)\n" " .data : 0x%p - 0x%p (%4ld kB)\n" " .text : 0x%p - 0x%p (%4ld kB)\n", (void*)VMALLOC_START, (void*)VMALLOC_END, (VMALLOC_END - VMALLOC_START) >> 20, diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c index f41aec8..0d54c6b 100644 --- a/arch/powerpc/kernel/sysfs.c +++ b/arch/powerpc/kernel/sysfs.c @@ -212,19 +212,19 @@ static SYSDEV_ATTR(purr, 0600, show_purr, store_purr); #endif /* CONFIG_PPC64 */ #ifdef HAS_PPC_PMC_PA6T SYSFS_PMCSETUP(pa6t_pmc0, SPRN_PA6T_PMC0); SYSFS_PMCSETUP(pa6t_pmc1, SPRN_PA6T_PMC1); SYSFS_PMCSETUP(pa6t_pmc2, SPRN_PA6T_PMC2); SYSFS_PMCSETUP(pa6t_pmc3, SPRN_PA6T_PMC3); SYSFS_PMCSETUP(pa6t_pmc4, SPRN_PA6T_PMC4); SYSFS_PMCSETUP(pa6t_pmc5, SPRN_PA6T_PMC5); -#ifdef CONFIG_DEBUG_KERNEL +#if 1 SYSFS_PMCSETUP(hid0, SPRN_HID0); SYSFS_PMCSETUP(hid1, SPRN_HID1); SYSFS_PMCSETUP(hid4, SPRN_HID4); SYSFS_PMCSETUP(hid5, SPRN_HID5); SYSFS_PMCSETUP(ima0, SPRN_PA6T_IMA0); SYSFS_PMCSETUP(ima1, SPRN_PA6T_IMA1); SYSFS_PMCSETUP(ima2, SPRN_PA6T_IMA2); SYSFS_PMCSETUP(ima3, SPRN_PA6T_IMA3); SYSFS_PMCSETUP(ima4, SPRN_PA6T_IMA4); @@ -282,19 +282,19 @@ static struct sysdev_attribute classic_pmc_attrs[] = { static struct sysdev_attribute pa6t_attrs[] = { _SYSDEV_ATTR(mmcr0, 0600, show_mmcr0, store_mmcr0), _SYSDEV_ATTR(mmcr1, 0600, show_mmcr1, store_mmcr1), _SYSDEV_ATTR(pmc0, 0600, show_pa6t_pmc0, store_pa6t_pmc0), _SYSDEV_ATTR(pmc1, 0600, show_pa6t_pmc1, store_pa6t_pmc1), _SYSDEV_ATTR(pmc2, 0600, show_pa6t_pmc2, store_pa6t_pmc2), _SYSDEV_ATTR(pmc3, 0600, show_pa6t_pmc3, store_pa6t_pmc3), _SYSDEV_ATTR(pmc4, 0600, show_pa6t_pmc4, store_pa6t_pmc4), _SYSDEV_ATTR(pmc5, 0600, show_pa6t_pmc5, store_pa6t_pmc5), -#ifdef CONFIG_DEBUG_KERNEL +#if 1 _SYSDEV_ATTR(hid0, 0600, show_hid0, store_hid0), _SYSDEV_ATTR(hid1, 0600, show_hid1, store_hid1), _SYSDEV_ATTR(hid4, 0600, show_hid4, store_hid4), _SYSDEV_ATTR(hid5, 0600, show_hid5, store_hid5), _SYSDEV_ATTR(ima0, 0600, show_ima0, store_ima0), _SYSDEV_ATTR(ima1, 0600, show_ima1, store_ima1), _SYSDEV_ATTR(ima2, 0600, show_ima2, store_ima2), _SYSDEV_ATTR(ima3, 0600, show_ima3, store_ima3), _SYSDEV_ATTR(ima4, 0600, show_ima4, store_ima4), > > +#define kpf_copy_bit(uflags, kflags, visible, ubit, kbit) \ > > + do { \ > > + if (visible || genuine_linus()) \ > > + uflags |= ((kflags >> kbit) & 1) << ubit; \ > > + } while (0); > > Did this have to be implemented as a macro? > > It's bad, because it might or might not reference its argument, so if > someone passes it an expression-with-side-effects, the end result is > unpredictable. A C function is almost always preferable if possible. Just tried inline function, the code size is increased slightly: text data bss dec hex filename macro 1804 128 0 1932 78c fs/proc/page.o inline 1828 128 0 1956 7a4 fs/proc/page.o So I'll keep the macro, but add brackets to make it a bit safer. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/