mm, printk: introduce new format string for flags

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>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 75 insertions, 0 deletions

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index f44e178e6ede..525c8e19bda2 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -35,6 +35,8 @@
 #include <linux/blkdev.h>
 #endif
 
+#include "../mm/internal.h"	/* For the trace_print_flags arrays */
+
 #include <asm/page.h>		/* for PAGE_SIZE */
 #include <asm/sections.h>	/* for dereference_function_descriptor() */
 #include <asm/byteorder.h>	/* cpu_to_le16 */
@@ -1407,6 +1409,72 @@ 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->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, 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;
 
 /*
@@ -1495,6 +1563,11 @@ 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 **
  *
@@ -1648,6 +1721,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 		return bdev_name(buf, end, ptr, spec, fmt);
 #endif
 
+	case 'G':
+		return flags_string(buf, end, ptr, fmt);
 	}
 	spec.flags |= SMALL;
 	if (spec.field_width == -1) {