[PATCH] coredump: optimize ->mm users traversal

zap_threads() iterates over all threads to find those ones which share
current->mm.  All threads in the thread group share the same ->mm, so we can
skip entire thread group if it has another ->mm.

This patch shifts the killing of thread group into the newly added
zap_process() function.  This looks as unnecessary complication, but it is
used in further patches.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 26 insertions, 10 deletions

diff --git a/fs/exec.c b/fs/exec.c
index fffea1eef8dc..80fe7bcfa094 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1368,6 +1368,22 @@ static void format_corename(char *corename, const char *pattern, long signr)
         *out_ptr = 0;
 }
 
+static void zap_process(struct task_struct *start, int *ptraced)
+{
+        struct task_struct *t;
+
+        t = start;
+        do {
+                if (t != current && t->mm) {
+                        t->mm->core_waiters++;
+                        force_sig_specific(SIGKILL, t);
+                        if (unlikely(t->ptrace) &&
+                            unlikely(t->parent->mm == t->mm))
+                                *ptraced = 1;
+                }
+        } while ((t = next_thread(t)) != start);
+}
+
 static void zap_threads (struct mm_struct *mm)
 {
         struct task_struct *g, *p;
@@ -1385,16 +1401,16 @@ static void zap_threads (struct mm_struct *mm)
         }
 
         read_lock(&tasklist_lock);
-        do_each_thread(g,p)
-                if (mm == p->mm && p != tsk) {
-                        force_sig_specific(SIGKILL, p);
-                        mm->core_waiters++;
-                        if (unlikely(p->ptrace) &&
-                            unlikely(p->parent->mm == mm))
-                                traced = 1;
-                }
-        while_each_thread(g,p);
-
+        for_each_process(g) {
+                p = g;
+                do {
+                        if (p->mm) {
+                                if (p->mm == mm)
+                                        zap_process(p, &traced);
+                                break;
+                        }
+                } while ((p = next_thread(p)) != g);
+        }
         read_unlock(&tasklist_lock);
 
         if (unlikely(traced)) {