kernel/pid.c: improve flow of a loop inside alloc_pidmap.

find_next_offset() searches for an available "cleaned bit" in the
respective pid bitmap (page), so returns the offset if found, otherwise
it returns a value equals to BITS_PER_PAGE.

For example, suppose find_next_offset didn't find any available bit, so
there's no purpose to call mk_pid (Wasteful Cpu Cycles).

Therefore, I found it could be better to call mk_pid after the checking
(offset < BITS_PER_PAGE) returned sucessfully! Another point: If (offset
< BITS_PER_PAGE) results in a "failure", then mk_pid would be called
again afterwards.

[akpm@linux-foundation.org: simplify code]
Signed-off-by: Raphael S. Carvalho <raphael.scarv@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/kernel/pid.c b/kernel/pid.c
index 047dc6264638..8147bdf22f36 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -183,15 +183,19 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
                                 break;
                 }
                 if (likely(atomic_read(&map->nr_free))) {
-                        do {
+                        for ( ; ; ) {
                                 if (!test_and_set_bit(offset, map->page)) {
                                         atomic_dec(&map->nr_free);
                                         set_last_pid(pid_ns, last, pid);
                                         return pid;
                                 }
                                 offset = find_next_offset(map, offset);
+                                if (offset >= BITS_PER_PAGE)
+                                        break;
                                 pid = mk_pid(pid_ns, map, offset);
-                        } while (offset < BITS_PER_PAGE && pid < pid_max);
+                                if (pid >= pid_max)
+                                        break;
+                        }
                 }
                 if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
                         ++map;