From: Oleg Nesterov Date: Sun, 8 Jan 2006 09:03:13 +0000 (-0800) Subject: [PATCH] do_coredump() should reset group_stop_count earlier X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=bb6f6dbaa48c53525a7a4f9d4df719c3b0b582af;p=GitHub%2FLineageOS%2Fandroid_kernel_samsung_universal7580.git [PATCH] do_coredump() should reset group_stop_count earlier __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 Signed-off-by: Linus Torvalds --- diff --git a/fs/exec.c b/fs/exec.c index 2075b674d85..fd02ea4a81e 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1462,6 +1462,7 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs) 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_code, struct pt_regs * regs) * 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)