[IA64] ptrace - find memory sharers on children list
In arch/ia64/kernel/ptrace.c there is a test for a peek or poke of a
register image (in register backing storage).
The test can be unnecessarily long (and occurs while holding the tasklist_lock).
Especially long on a large system with thousands of active tasks.
The ptrace caller (presumably a debugger) specifies the pid of
its target and an address to peek or poke. But the debugger could be
attached to several tasks.
The idea of find_thread_for_addr() is to find whether the target address
is in the RBS for any of those tasks.
Currently it searches the thread-list of the target pid. If that search
does not find a match, and the shared mm-struct's user count indicates
that there are other tasks sharing this address space (a rare occurrence),
a search is made of all the tasks in the system.
Another approach can drastically shorten this procedure.
It depends upon the fact that in order to peek or poke from/to any task,
the debugger must first attach to that task. And when it does, the
attached task is made a child of the debugger (is chained to its children list).
Therefore we can search just the debugger's children list.
Signed-off-by: Cliff Wickman <cpw@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c
index bbb8bc7..9a9c1bd 100644
--- a/arch/ia64/kernel/ptrace.c
+++ b/arch/ia64/kernel/ptrace.c
@@ -589,6 +589,7 @@
{
struct task_struct *g, *p;
struct mm_struct *mm;
+ struct list_head *this, *next;
int mm_users;
if (!(mm = get_task_mm(child)))
@@ -600,28 +601,21 @@
goto out; /* not multi-threaded */
/*
- * First, traverse the child's thread-list. Good for scalability with
- * NPTL-threads.
+ * Traverse the current process' children list. Every task that
+ * one attaches to becomes a child. And it is only attached children
+ * of the debugger that are of interest (ptrace_check_attach checks
+ * for this).
*/
- p = child;
- do {
- if (thread_matches(p, addr)) {
- child = p;
- goto out;
- }
- if (mm_users-- <= 1)
- goto out;
- } while ((p = next_thread(p)) != child);
-
- do_each_thread(g, p) {
- if (child->mm != mm)
+ list_for_each_safe(this, next, ¤t->children) {
+ p = list_entry(this, struct task_struct, sibling);
+ if (p->mm != mm)
continue;
-
if (thread_matches(p, addr)) {
child = p;
goto out;
}
- } while_each_thread(g, p);
+ }
+
out:
mmput(mm);
return child;