From 4ac0068f44f192f2de95a7bb36df3e19767a45fb Mon Sep 17 00:00:00 2001 From: Cliff Wickman Date: Thu, 27 Oct 2005 10:29:08 -0500 Subject: [PATCH] [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 Signed-off-by: Tony Luck --- arch/ia64/kernel/ptrace.c | 26 ++++++++++---------------- 1 file changed, 10 insertions(+), 16 deletions(-) diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c index bbb8bc7c055..9a9c1bd01db 100644 --- a/arch/ia64/kernel/ptrace.c +++ b/arch/ia64/kernel/ptrace.c @@ -589,6 +589,7 @@ find_thread_for_addr (struct task_struct *child, unsigned long addr) { 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 @@ find_thread_for_addr (struct task_struct *child, unsigned long addr) 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; -- 2.20.1