Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755200AbbLBUex (ORCPT ); Wed, 2 Dec 2015 15:34:53 -0500 Received: from mx2.suse.de ([195.135.220.15]:36969 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751775AbbLBUew (ORCPT ); Wed, 2 Dec 2015 15:34:52 -0500 Subject: Re: [PATCH 1/2] mm, printk: introduce new format string for flags To: Rasmus Villemoes References: <20151125143010.GI27283@dhcp22.suse.cz> <1448899821-9671-1-git-send-email-vbabka@suse.cz> <87io4hi06n.fsf@rasmusvillemoes.dk> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Joonsoo Kim , Minchan Kim , Sasha Levin , "Kirill A. Shutemov" , Mel Gorman , Michal Hocko From: Vlastimil Babka X-Enigmail-Draft-Status: N1110 Message-ID: <565F55E6.6080201@suse.cz> Date: Wed, 2 Dec 2015 21:34:46 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <87io4hi06n.fsf@rasmusvillemoes.dk> Content-Type: text/plain; charset=iso-8859-2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6522 Lines: 192 On 12/02/2015 12:01 PM, Rasmus Villemoes wrote: > On Mon, Nov 30 2015, Vlastimil Babka wrote: > > I'd prefer to have the formatting code in vsprintf.c, so that we'd avoid > having to call vsnprintf recursively (and repeatedly - not that this is > going to be used in hot paths, but if the box is going down it might be > nice to get the debug info out a few thousand cycles earlier). That'll > also make it easier to avoid the bugs below. OK, I'll try. >> diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt >> index b784c270105f..4b5156e74b09 100644 >> --- a/Documentation/printk-formats.txt >> +++ b/Documentation/printk-formats.txt >> @@ -292,6 +292,20 @@ Raw pointer value SHOULD be printed with %p. The kernel supports >> >> Passed by reference. >> >> +Flags bitfields such as page flags, gfp_flags: >> + >> + %pgp 0x1fffff8000086c(referenced|uptodate|lru|active|private) >> + %pgg 0x24202c4(GFP_USER|GFP_DMA32|GFP_NOWARN) >> + %pgv 0x875(read|exec|mayread|maywrite|mayexec|denywrite) >> + > > I think it would be better (and more flexible) if %pg* only stood for > printing the | chain of strings. Let people pass the flags twice if they > also want the numeric value; then they're also able to choose 0-padding > and whatnot, can use other kinds of parentheses, etc., etc. So > > pr_emerg("flags: 0x%08lu [%pgp]\n", printflags, &printflags) I had it initially like this, but then thought it was somewhat repetitive and all current users did use the same format. But I agree it's more generic to do it as you say so I'll change it. >> @@ -1361,6 +1362,29 @@ char *clock(char *buf, char *end, struct clk *clk, struct printf_spec spec, >> } >> } >> >> +static noinline_for_stack >> +char *flags_string(char *buf, char *end, void *flags_ptr, >> + struct printf_spec spec, const char *fmt) >> +{ >> + unsigned long flags; >> + gfp_t gfp_flags; >> + >> + switch (fmt[1]) { >> + case 'p': >> + flags = *(unsigned long *)flags_ptr; >> + return format_page_flags(flags, buf, end); >> + case 'v': >> + flags = *(unsigned long *)flags_ptr; >> + return format_vma_flags(flags, buf, end); >> + case 'g': >> + gfp_flags = *(gfp_t *)flags_ptr; >> + return format_gfp_flags(gfp_flags, buf, end); >> + default: >> + WARN_ONCE(1, "Unsupported flags modifier: %c\n", fmt[1]); >> + return 0; >> + } >> +} >> + > > That return 0 aka return NULL will lead to an oops when the next thing > is printed. Did you mean 'return buf;'? Uh, right. >> >> -static void dump_flag_names(unsigned long flags, >> - const struct trace_print_flags *names, int count) >> +static char *format_flag_names(unsigned long flags, unsigned long mask_out, >> + const struct trace_print_flags *names, int count, >> + char *buf, char *end) >> { >> const char *delim = ""; >> unsigned long mask; >> int i; >> >> - pr_cont("("); >> + buf += snprintf(buf, end - buf, "%#lx(", flags); > > Sorry, you can't do it like this. The buf you've been passed from inside > vsnprintf may be beyond end Ah, didn't realize that :/ > , so end-buf is a negative number which will > (get converted to a huge positive size_t and) trigger a WARN_ONCE and > get you a return value of 0. > > >> + flags &= ~mask_out; >> >> for (i = 0; i < count && flags; i++) { >> + if (buf >= end) >> + break; > > Even if you fix the above, this is also wrong. We have to return the > length of the string that would be generated if there was room enough, > so we cannot make an early return like this. As I said above, the > easiest way to do that is to do it inside vsprintf.c, where we have > e.g. string() available. So I'd do something like > > > char *format_flags(char *buf, char *end, unsigned long flags, > const struct trace_print_flags *names) > { > unsigned long mask; > const struct printf_spec strspec = {/* appropriate defaults*/} > const struct printf_spec numspec = {/* appropriate defaults*/} > > for ( ; flags && names->mask; names++) { > mask = names->mask; > if ((flags & mask) != mask) > continue; > flags &= ~mask; > buf = string(buf, end, names->name, strspec); > if (flags) { > if (buf < end) > *buf = '|'; > buf++; > } > } > if (flags) > buf = number(buf, end, flags, numspec); > return buf; > } Thanks a lot for your review and suggestions! > [where I've assumed that the trace_print_flags array is terminated with > an entry with 0 mask. Passing its length is also possible, but maybe a > little awkward if the arrays are defined in mm/ and contents depend on > .config.] > Then flags_string() would call this directly with an appropriate array > for names, and we avoid the individual tiny helper > functions. flags_string() can still do the mask_out thing for page > flags, especially when/if the numeric and string representations are not > done at the same time. > > Rasmus Zero-terminated array is a good idea to get rid of the ARRAY_SIZE with helpers needing to live in the same .c file etc. But if I were to keep the array definitions in mm/debug.c with declarations (which don't know the size yet) in e.g. (which lib/vsnprintf.c would include so that format_flags() can reference them, is there a more elegant way than the one below? --- a/include/linux/mmdebug.h +++ b/include/linux/mmdebug.h @@ -7,6 +7,9 @@ struct page; struct vm_area_struct; struct mm_struct; +struct trace_print_flags; // can't include trace_events.h here + +extern const struct trace_print_flags *pageflag_names; extern void dump_page(struct page *page, const char *reason); extern void dump_page_badflags(struct page *page, const char *reason, diff --git a/mm/debug.c b/mm/debug.c index a092111920e7..1cbc60544b87 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -23,7 +23,7 @@ char *migrate_reason_names[MR_TYPES] = { "cma", }; -static const struct trace_print_flags pageflag_names[] = { +const struct trace_print_flags __pageflag_names[] = { {1UL << PG_locked, "locked" }, {1UL << PG_error, "error" }, {1UL << PG_referenced, "referenced" }, @@ -59,6 +59,8 @@ static const struct trace_print_flags pageflag_names[] = { #endif }; +const struct trace_print_flags *pageflag_names = &__pageflag_names[0]; -- 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/