From: Oleg Nesterov __group_complete_signal() sets ->group_stop_count in sig_kernel_coredump() path and marks the target thread as ->group_exit_task. So any thread except group_exit_task will go to handle_group_stop()->finish_stop(). However, when group_exit_task actually starts do_coredump(), it sets SIGNAL_GROUP_EXIT, but does not reset ->group_stop_count while killing other threads. If we have not yet stopped threads in the same thread group, they all will spin in kernel mode until group_exit_task sends them SIGKILL, because ->group_stop_count > 0 means: recalc_sigpending_tsk() never clears TIF_SIGPENDING get_signal_to_deliver() goes to handle_group_stop() handle_group_stop() returns when SIGNAL_GROUP_EXIT set syscall_exit/resume_userspace notice TIF_SIGPENDING, call get_signal_to_deliver() again. So we are wasting cpu cycles, and if one of these threads is rt_task() this may be a serious problem. NOTE: do_coredump() holds ->mmap_sem, so not stopped threads can't escape coredumping after clearing ->group_stop_count. See also this thread: http://marc.theaimsgroup.com/?t=112739139900002 Signed-off-by: Oleg Nesterov Signed-off-by: Andrew Morton --- fs/exec.c | 2 +- 1 files changed, 1 insertion(+), 1 deletion(-) diff -puN fs/exec.c~do_coredump-should-reset-group_stop_count-earlier fs/exec.c --- devel/fs/exec.c~do_coredump-should-reset-group_stop_count-earlier 2005-12-10 21:52:25.000000000 -0800 +++ devel-akpm/fs/exec.c 2005-12-10 21:52:25.000000000 -0800 @@ -1462,6 +1462,7 @@ int do_coredump(long signr, int exit_cod if (!(current->signal->flags & SIGNAL_GROUP_EXIT)) { current->signal->flags = SIGNAL_GROUP_EXIT; current->signal->group_exit_code = exit_code; + current->signal->group_stop_count = 0; retval = 0; } spin_unlock_irq(¤t->sighand->siglock); @@ -1477,7 +1478,6 @@ int do_coredump(long signr, int exit_cod * Clear any false indication of pending signals that might * be seen by the filesystem code called to write the core file. */ - current->signal->group_stop_count = 0; clear_thread_flag(TIF_SIGPENDING); if (current->signal->rlim[RLIMIT_CORE].rlim_cur < binfmt->min_coredump) _