coredump: cn_vprintf() has no reason to call vsnprintf() twice

cn_vprintf() looks really overcomplicated and sub-optimal.  We do not need
vsnprintf(NULL) to calculate the size we need, we can simply try to print
into the current buffer and expand/retry only if necessary.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Colin Walters <walters@verbum.org>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Lennart Poettering <mzxreary@0pointer.de>
Cc: Lucas De Marchi <lucas.de.marchi@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 18 deletions

diff --git a/fs/coredump.c b/fs/coredump.c
index c10a43aae220..2b1d1f54e630 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -71,26 +71,20 @@ static int expand_corename(struct core_name *cn)
 
 static int cn_vprintf(struct core_name *cn, const char *fmt, va_list arg)
 {
-        char *cur;
-        int need;
-        int ret;
-
-        need = vsnprintf(NULL, 0, fmt, arg);
-        if (likely(need < cn->size - cn->used - 1))
-                goto out_printf;
-
-        ret = expand_corename(cn);
-        if (ret)
-                goto expand_fail;
+        int free, need;
+
+again:
+        free = cn->size - cn->used;
+        need = vsnprintf(cn->corename + cn->used, free, fmt, arg);
+        if (need < free) {
+                cn->used += need;
+                return 0;
+        }
 
-out_printf:
-        cur = cn->corename + cn->used;
-        vsnprintf(cur, need + 1, fmt, arg);
-        cn->used += need;
-        return 0;
+        if (!expand_corename(cn))
+                goto again;
 
-expand_fail:
-        return ret;
+        return -ENOMEM;
 }
 
 static int cn_printf(struct core_name *cn, const char *fmt, ...)