Re: [PATCH v2 1/3] mm, printk: introduce new format string for flags

Steven Rostedt
2015-12-10T03:51:33Z

I should have been Cc'd on this as I'm the maintainer of a few of the files
here that is being modified.

On Fri, Dec 04, 2015 at 04:16:33PM +0100, Vlastimil Babka wrote:
> In mm we use several kinds of flags bitfields that are sometimes printed for
> debugging purposes, or exported to userspace via sysfs. To make them easier to
> interpret independently on kernel version and config, we want to dump also the
> symbolic flag names. So far this has been done with repeated calls to
> pr_cont(), which is unreliable on SMP, and not usable for e.g. sysfs export.
>
> To get a more reliable and universal solution, this patch extends printk()
> format string for pointers to handle the page flags (%pgp), gfp_flags (%pgg)
> and vma flags (%pgv). Existing users of dump_flag_names() are converted and
> simplified.
>
> It would be possible to pass flags by value instead of pointer, but the %p
> format string for pointers already has extensions for various kernel
> structures, so it's a good fit, and the extra indirection in a non-critical
> path is negligible.
>
> [linux@rasmusvillemoes.dk: lots of good implementation suggestions]
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Sasha Levin <sasha.levin@oracle.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Michal Hocko <mhocko@suse.cz>
> ---
> Should hopefully apply to mmots (release mmotm doesn't have the 3 -fix patches yet?)
>
> Documentation/printk-formats.txt | 14 ++++
> include/linux/mmdebug.h | 7 +-
> include/linux/trace_events.h | 10 ---
> include/linux/tracepoint.h | 10 +++
> lib/vsprintf.c | 75 ++++++++++++++++++++++
> mm/debug.c | 135 ++++++++++++++-------------------------
> mm/oom_kill.c | 5 +-
> mm/page_alloc.c | 5 +-
> mm/page_owner.c | 6 +-
> 9 files changed, 160 insertions(+), 107 deletions(-)
>
> diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
> index b784c270105f..8b6ab00fcfc9 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 referenced|uptodate|lru|active|private
> + %pgg GFP_USER|GFP_DMA32|GFP_NOWARN
> + %pgv read|exec|mayread|maywrite|mayexec|denywrite
> +
> + For printing flags bitfields as a collection of symbolic constants that
> + would construct the value. The type of flags is given by the third
> + character. Currently supported are [p]age flags, [g]fp_flags and
> + [v]ma_flags. The flag names and print order depends on the particular
> + type.
> +
> + Passed by reference.
> +
> Network device features:
>
> %pNF 0x000000000000c000
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index 3b77fab7ad28..2c8286cf162e 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -2,15 +2,20 @@
> #define LINUX_MM_DEBUG_H 1
>
> #include <linux/stringify.h>
> +#include <linux/types.h>
> +#include <linux/tracepoint.h>
>
> struct page;
> struct vm_area_struct;
> struct mm_struct;
>
> +extern const struct trace_print_flags pageflag_names[];
> +extern const struct trace_print_flags vmaflag_names[];
> +extern const struct trace_print_flags gfpflag_names[];
> +
> extern void dump_page(struct page *page, const char *reason);
> extern void dump_page_badflags(struct page *page, const char *reason,
> unsigned long badflags);
> -extern void dump_gfpflag_names(unsigned long gfp_flags);
> void dump_vma(const struct vm_area_struct *vma);
> void dump_mm(const struct mm_struct *mm);
>
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 429fdfc3baf5..d91404f89ff2 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -15,16 +15,6 @@ struct tracer;
> struct dentry;
> struct bpf_prog;
>
> -struct trace_print_flags {
> - unsigned long mask;
> - const char *name;
> -};
> -
> -struct trace_print_flags_u64 {
> - unsigned long long mask;
> - const char *name;
> -};
> -

Ingo took some patches from Andi Kleen that creates a tracepoint-defs.h file
If anything, these should be moved there. That code is currently in tip.

-- Steve

> const char *trace_print_flags_seq(struct trace_seq *p, const char *delim,
> unsigned long flags,
> const struct trace_print_flags *flag_array);
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 7834a8a8bf1e..a5d0ab46724d 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -43,6 +43,16 @@ struct trace_enum_map {
> unsigned long enum_value;
> };
>
> +struct trace_print_flags {
> + unsigned long mask;
> + const char *name;
> +};
> +
> +struct trace_print_flags_u64 {
> + unsigned long long mask;
> + const char *name;
> +};
> +
> #define TRACEPOINT_DEFAULT_PRIO 10
>
> extern int
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index f9cee8e1233c..9a0697b14ea3 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -31,6 +31,7 @@
> #include <linux/dcache.h>
> #include <linux/cred.h>
> #include <net/addrconf.h>
> +#include <linux/mmdebug.h>
>
> #include <asm/page.h> /* for PAGE_SIZE */
> #include <asm/sections.h> /* for dereference_function_descriptor() */
> @@ -1361,6 +1362,73 @@ char *clock(char *buf, char *end, struct clk *clk, struct printf_spec spec,
> }
> }
>
> +static
> +char *format_flags(char *buf, char *end, unsigned long flags,
> + const struct trace_print_flags *names)
> +{
> + unsigned long mask;
> + const struct printf_spec strspec = {
> + .field_width = -1,
> + .precision = -1,
> + };
> + const struct printf_spec numspec = {
> + .flags = SPECIAL|SMALL,
> + .field_width = -1,
> + .precision = -1,
> + .base = 16,
> + };
> +
> + for ( ; flags && (names->mask || names->name); names++) {
> + mask = names->mask;
> + if ((flags & mask) != mask)
> + continue;
> +
> + buf = string(buf, end, names->name, strspec);
> +
> + flags &= ~mask;
> + if (flags) {
> + if (buf < end)
> + *buf = '|';
> + buf++;
> + }
> + }
> +
> + if (flags)
> + buf = number(buf, end, flags, numspec);
> +
> + return buf;
> +}
> +
> +static noinline_for_stack
> +char *flags_string(char *buf, char *end, void *flags_ptr,
> + struct printf_spec spec, const char *fmt)
> +{
> + unsigned long flags;
> + const struct trace_print_flags *names;
> +
> + switch (fmt[1]) {
> + case 'p':
> + flags = *(unsigned long *)flags_ptr;
> + /* Remove zone id */
> + flags &= (1UL << NR_PAGEFLAGS) - 1;
> + names = pageflag_names;
> + break;
> + case 'v':
> + flags = *(unsigned long *)flags_ptr;
> + names = vmaflag_names;
> + break;
> + case 'g':
> + flags = *(gfp_t *)flags_ptr;
> + names = gfpflag_names;
> + break;
> + default:
> + WARN_ONCE(1, "Unsupported flags modifier: %c\n", fmt[1]);
> + return buf;
> + }
> +
> + return format_flags(buf, end, flags, names);
> +}
> +
> int kptr_restrict __read_mostly;
>
> /*
> @@ -1448,6 +1516,11 @@ int kptr_restrict __read_mostly;
> * - 'Cn' For a clock, it prints the name (Common Clock Framework) or address
> * (legacy clock framework) of the clock
> * - 'Cr' For a clock, it prints the current rate of the clock
> + * - 'g' For flags to be printed as a collection of symbolic strings that would
> + * construct the specific value. Supported flags given by option:
> + * p page flags (see struct page) given as pointer to unsigned long
> + * g gfp flags (GFP_* and __GFP_*) given as pointer to gfp_t
> + * v vma flags (VM_*) given as pointer to unsigned long
> *
> * ** Please update also Documentation/printk-formats.txt when making changes **
> *
> @@ -1600,6 +1673,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> return dentry_name(buf, end,
> ((const struct file *)ptr)->f_path.dentry,
> spec, fmt);
> + case 'g':
> + return flags_string(buf, end, ptr, spec, fmt);
> }
> spec.flags |= SMALL;
> if (spec.field_width == -1) {
> diff --git a/mm/debug.c b/mm/debug.c
> index 9416524839d8..c42bb4c13c2d 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" },
> @@ -57,86 +57,10 @@ static const struct trace_print_flags pageflag_names[] = {
> {1UL << PG_young, "young" },
> {1UL << PG_idle, "idle" },
> #endif
> + {0, NULL },
> };
>
> -static const struct trace_print_flags gfpflag_names[] = {
> - __def_gfpflag_names
> -};
> -
> -static void dump_flag_names(unsigned long flags,
> - const struct trace_print_flags *names, int count)
> -{
> - const char *delim = "";
> - unsigned long mask;
> - int i;
> -
> - pr_cont("(");
> -
> - for (i = 0; i < count && flags; i++) {
> -
> - mask = names[i].mask;
> - if ((flags & mask) != mask)
> - continue;
> -
> - flags &= ~mask;
> - pr_cont("%s%s", delim, names[i].name);
> - delim = "|";
> - }
> -
> - /* check for left over flags */
> - if (flags)
> - pr_cont("%s%#lx", delim, flags);
> -
> - pr_cont(")\n");
> -}
> -
> -void dump_gfpflag_names(unsigned long gfp_flags)
> -{
> - dump_flag_names(gfp_flags, gfpflag_names, ARRAY_SIZE(gfpflag_names));
> -}
> -
> -void dump_page_badflags(struct page *page, const char *reason,
> - unsigned long badflags)
> -{
> - unsigned long printflags = page->flags;
> -
> - pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx",
> - page, atomic_read(&page->_count), page_mapcount(page),
> - page->mapping, page->index);
> - if (PageCompound(page))
> - pr_cont(" compound_mapcount: %d", compound_mapcount(page));
> - pr_cont("\n");
> - BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS);
> -
> - pr_emerg("flags: %#lx", printflags);
> - /* remove zone id */
> - printflags &= (1UL << NR_PAGEFLAGS) - 1;
> - dump_flag_names(printflags, pageflag_names, ARRAY_SIZE(pageflag_names));
> -
> - if (reason)
> - pr_alert("page dumped because: %s\n", reason);
> - if (page->flags & badflags) {
> - printflags = page->flags & badflags;
> - pr_alert("bad because of flags: %#lx:", printflags);
> - dump_flag_names(printflags, pageflag_names,
> - ARRAY_SIZE(pageflag_names));
> - }
> -#ifdef CONFIG_MEMCG
> - if (page->mem_cgroup)
> - pr_alert("page->mem_cgroup:%p\n", page->mem_cgroup);
> -#endif
> -}
> -
> -void dump_page(struct page *page, const char *reason)
> -{
> - dump_page_badflags(page, reason, 0);
> - dump_page_owner(page);
> -}
> -EXPORT_SYMBOL(dump_page);
> -
> -#ifdef CONFIG_DEBUG_VM
> -
> -static const struct trace_print_flags vmaflags_names[] = {
> +const struct trace_print_flags vmaflag_names[] = {
> {VM_READ, "read" },
> {VM_WRITE, "write" },
> {VM_EXEC, "exec" },
> @@ -177,22 +101,61 @@ static const struct trace_print_flags vmaflags_names[] = {
> {VM_HUGEPAGE, "hugepage" },
> {VM_NOHUGEPAGE, "nohugepage" },
> {VM_MERGEABLE, "mergeable" },
> + {0, NULL },
> +};
> +
> +const struct trace_print_flags gfpflag_names[] = {
> + __def_gfpflag_names,
> + {0, NULL},
> };
>
> +void dump_page_badflags(struct page *page, const char *reason,
> + unsigned long badflags)
> +{
> + unsigned long printflags = page->flags;
> +
> + pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx\n",
> + page, atomic_read(&page->_count), page_mapcount(page),
> + page->mapping, page->index);
> + BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
> +
> + pr_emerg("flags: %#lx(%pgp)\n", printflags, &printflags);
> +
> + if (reason)
> + pr_alert("page dumped because: %s\n", reason);
> + if (page->flags & badflags) {
> + printflags = page->flags & badflags;
> + pr_alert("bad because of flags: %#lx(%pgp)\n", printflags,
> + &printflags);
> + }
> +#ifdef CONFIG_MEMCG
> + if (page->mem_cgroup)
> + pr_alert("page->mem_cgroup:%p\n", page->mem_cgroup);
> +#endif
> +}
> +
> +void dump_page(struct page *page, const char *reason)
> +{
> + dump_page_badflags(page, reason, 0);
> + dump_page_owner(page);
> +}
> +EXPORT_SYMBOL(dump_page);
> +
> +#ifdef CONFIG_DEBUG_VM
> +
> void dump_vma(const struct vm_area_struct *vma)
> {
> pr_emerg("vma %p start %p end %p\n"
> "next %p prev %p mm %p\n"
> "prot %lx anon_vma %p vm_ops %p\n"
> - "pgoff %lx file %p private_data %p\n",
> + "pgoff %lx file %p private_data %p\n"
> + "flags: %#lx(%pgv)\n",
> vma, (void *)vma->vm_start, (void *)vma->vm_end, vma->vm_next,
> vma->vm_prev, vma->vm_mm,
> (unsigned long)pgprot_val(vma->vm_page_prot),
> vma->anon_vma, vma->vm_ops, vma->vm_pgoff,
> - vma->vm_file, vma->vm_private_data);
> - pr_emerg("flags: %#lx", vma->vm_flags);
> - dump_flag_names(vma->vm_flags, vmaflags_names,
> - ARRAY_SIZE(vmaflags_names));
> + vma->vm_file, vma->vm_private_data,
> + vma->vm_flags, &vma->vm_flags);
> }
> EXPORT_SYMBOL(dump_vma);
>
> @@ -263,9 +226,7 @@ void dump_mm(const struct mm_struct *mm)
> "" /* This is here to not have a comma! */
> );
>
> - pr_emerg("def_flags: %#lx", mm->def_flags);
> - dump_flag_names(mm->def_flags, vmaflags_names,
> - ARRAY_SIZE(vmaflags_names));
> + pr_emerg("def_flags: %#lx(%pgv)\n", mm->def_flags, &mm->def_flags);
> }
>
> #endif /* CONFIG_DEBUG_VM */
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 542d56c93209..07bba5a46b47 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -387,10 +387,9 @@ static void dump_header(struct oom_control *oc, struct task_struct *p,
> struct mem_cgroup *memcg)
> {
> pr_warning("%s invoked oom-killer: order=%d, oom_score_adj=%hd, "
> - "gfp_mask=0x%x",
> + "gfp_mask=%#x(%pgg)\n",
> current->comm, oc->order, current->signal->oom_score_adj,
> - oc->gfp_mask);
> - dump_gfpflag_names(oc->gfp_mask);
> + oc->gfp_mask, &oc->gfp_mask);
>
> cpuset_print_current_mems_allowed();
> dump_stack();
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d6d7c97c0b28..bd94c7465dea 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2711,9 +2711,8 @@ void warn_alloc_failed(gfp_t gfp_mask, unsigned int order, const char *fmt, ...)
> va_end(args);
> }
>
> - pr_warn("%s: page allocation failure: order:%u, mode:0x%x",
> - current->comm, order, gfp_mask);
> - dump_gfpflag_names(gfp_mask);
> + pr_warn("%s: page allocation failure: order:%u, mode:%#x(%pgg)\n",
> + current->comm, order, gfp_mask, &gfp_mask);
> dump_stack();
> if (!should_suppress_show_mem())
> show_mem(filter);
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index f4acd2452c35..313251f36d86 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -208,9 +208,9 @@ void __dump_page_owner(struct page *page)
> return;
> }
>
> - pr_alert("page allocated via order %u, migratetype %s, gfp_mask 0x%x",
> - page_ext->order, migratetype_names[mt], gfp_mask);
> - dump_gfpflag_names(gfp_mask);
> + pr_alert("page allocated via order %u, migratetype %s, "
> + "gfp_mask %#x(%pgg)\n", page_ext->order,
> + migratetype_names[mt], gfp_mask, &gfp_mask);
> print_stack_trace(&trace, 0);
>
> if (page_ext->last_migrate_reason != -1)
> --
> 2.6.3
>
> --
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