Re: [RFC PATCH] set TASK_TRACED before arch_ptrace code to fix a race

["Luming Yu" <luming.yu@gmail.com>]

>
> if happens, it should be a bug, right?

It does happen!!

Call Trace:
 [<a000000100011bd0>] show_stack+0x50/0xa0
                                spà00000146bbfbb0 bspà00000146bb0e08
 [<a000000100011c50>] dump_stack+0x30/0x60
                                spà00000146bbfd80 bspà00000146bb0de8
 [<a0000001000979a0>] get_signal_to_deliver+0x60/0x6e0
                                spà00000146bbfd80 bspà00000146bb0d80
 [<a0000001000343d0>] ia64_do_signal+0xb0/0xd00
                                spà00000146bbfd80 bspà00000146bb0cd8
 [<a000000100012650>] do_notify_resume_user+0xf0/0x140
                                spà00000146bbfe20 bspà00000146bb0ca8
 [<a00000010000aac0>] notify_resume_user+0x40/0x60
                                spà00000146bbfe20 bspà00000146bb0c58
 [<a00000010000a9f0>] skip_rbs_switch+0xe0/0x110
                                spà00000146bbfe30 bspà00000146bb0c58
 [<a000000000010740>] __kernel_syscall_via_break+0x0/0x20
                                spà00000146bc0000 bspà00000146bb0c58

>>
> I will try to customize kernel to capture call trace for a precise code path.

I applied the following patch , and got the call trace above..
If apply my RFC patch as antidote,  I don't see "deliver" ...
Is the problem clear now?  I will serve you until every thing is clear to you.

Thanks,
Luming

Signed-off-by: Yu Luming <luming.yu@intel.com>

diff -Bru 1/kernel/signal.c 0/kernel/signal.c
--- 1/kernel/signal.c   2008-05-27 15:18:48.000000000 +0800
+++ 0/kernel/signal.c   2008-05-27 15:08:51.000000000 +0800
@@ -38,6 +38,7 @@
  */

 static struct kmem_cache *sigqueue_cachep;
+unsigned long global_arch_ptrace_stop_flag =0;

 static int __sig_ignored(struct task_struct *t, int sig)
 {
@@ -1501,9 +1502,12 @@
                 * siglock.  That must prevent us from sleeping in TASK_TRACED.
                 * So after regaining the lock, we must check for SIGKILL.
                 */
+               global_arch_ptrace_stop_flag = 1;
                spin_unlock_irq(&current->sighand->siglock);
                arch_ptrace_stop(exit_code, info);
+
                spin_lock_irq(&current->sighand->siglock);
+               global_arch_ptrace_stop_flag = 0;
                killed = sigkill_pending(current);
        }

@@ -1701,6 +1705,8 @@
        struct signal_struct *signal = current->signal;
        int signr;

+       if (global_arch_ptrace_stop_flag)
+               dump_stack();
 relock:
        /*
         * We'll jump back here after any time we were stopped in TASK_STOPPED.