From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Eric W. Biederman" Subject: [PATCH 17/26] exit: Rework the exit states for ptracees Date: Tue, 6 Jun 2017 14:03:29 -0500 Message-ID: <20170606190338.28347-17-ebiederm@xmission.com> References: <877f0pym71.fsf@xmission.com> <20170606190338.28347-1-ebiederm@xmission.com> Return-path: In-Reply-To: <20170606190338.28347-1-ebiederm@xmission.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: linux-api@vger.kernel.org, Linus Torvalds , Oleg Nesterov , Ingo Molnar , Thomas Gleixner , Kees Cook , Roland McGrath , Al Viro , David Howells , "Michael Kerrisk (man-pages)" , "Eric W. Biederman" List-Id: linux-api@vger.kernel.org Create two new exit states EXIT_TRACEE and EXIT_TRACED replacing the two states "(EXIT_ZOMBIE && (!thread_group_leader(p) || !ptrace_reparented)) and EXIT_TRACE. With EXIT_ZOMBIE replacing the state: "(EXIT_ZOMBIE && thread_group_leader(p) && !ptrace_reparented)". Rework the code to take advantage of the certain knowledge of exit state progression: EXIT_TRACEE -> EXIT_TRACED -> EXIT_ZOMBIE -> EXIT_DEAD This makes the code more readable/maintainable by using simple states rather than complicated expressions. The values of both of the new states contain EXIT_ZOMBIE so all of these states appear to userspace as zombies. Signed-off-by: "Eric W. Biederman" --- include/linux/sched.h | 6 +++++- kernel/exit.c | 51 +++++++++++++++++++++++---------------------------- kernel/ptrace.c | 31 +++++++++++++++++-------------- 3 files changed, 45 insertions(+), 43 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 461ecd20731c..f2cec7f27e59 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -73,7 +73,6 @@ struct task_group; /* Used in tsk->exit_state: */ #define EXIT_DEAD 16 #define EXIT_ZOMBIE 32 -#define EXIT_TRACE (EXIT_ZOMBIE | EXIT_DEAD) /* Used in tsk->state again: */ #define TASK_DEAD 64 #define TASK_WAKEKILL 128 @@ -82,6 +81,11 @@ struct task_group; #define TASK_NOLOAD 1024 #define TASK_NEW 2048 #define TASK_STATE_MAX 4096 +/* Used in tsk->exit_state again: */ +#define __EXIT_TRACEE 8192 +#define __EXIT_TRACED 16384 +#define EXIT_TRACEE (EXIT_ZOMBIE | __EXIT_TRACEE) +#define EXIT_TRACED (EXIT_ZOMBIE | __EXIT_TRACED) #define TASK_STATE_TO_CHAR_STR "RSDTtXZxKWPNn" diff --git a/kernel/exit.c b/kernel/exit.c index 72591eb5e361..ff2ed1d60a8c 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -580,8 +580,7 @@ static void reparent_leader(struct task_struct *father, struct task_struct *p, p->exit_signal = SIGCHLD; /* If it has exited notify the new parent about this child's death. */ - if (!p->ptrace && - p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) { + if (p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) { if (do_notify_parent(p, p->exit_signal)) { p->exit_state = EXIT_DEAD; list_add(&p->ptrace_entry, dead); @@ -639,7 +638,7 @@ static void forget_original_parent(struct task_struct *father, */ static void exit_notify(struct task_struct *tsk, int group_dead) { - bool autoreap = true; + int state = EXIT_DEAD; struct task_struct *p, *n; LIST_HEAD(dead); @@ -650,14 +649,18 @@ static void exit_notify(struct task_struct *tsk, int group_dead) kill_orphaned_pgrp(tsk->group_leader, NULL); if (thread_group_leader(tsk) && !ptrace_reparented(tsk)) { - autoreap = thread_group_empty(tsk) && - do_notify_parent(tsk, tsk->exit_signal); + state = EXIT_ZOMBIE; + if (thread_group_empty(tsk) && + do_notify_parent(tsk, tsk->exit_signal)) + state = EXIT_DEAD; } else if (unlikely(tsk->ptrace)) { - autoreap = do_notify_parent(tsk, SIGCHLD); + state = EXIT_TRACEE; + if (do_notify_parent(tsk, SIGCHLD)) + state = EXIT_DEAD; } - tsk->exit_state = autoreap ? EXIT_DEAD : EXIT_ZOMBIE; + tsk->exit_state = state; if (tsk->exit_state == EXIT_DEAD) list_add(&tsk->ptrace_entry, &dead); @@ -1001,7 +1004,7 @@ static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p, * the lock and this task is uninteresting. If we return nonzero, we have * released the lock and the system call should return. */ -static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p) +static int wait_task_zombie(struct wait_opts *wo, int old_state, struct task_struct *p) { int state, retval, status; pid_t pid = task_pid_vnr(p); @@ -1029,11 +1032,11 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p) return wait_noreap_copyout(wo, p, pid, uid, why, status); } /* - * Move the task's state to DEAD/TRACE, only one thread can do this. + * Move the task's state to DEAD/TRACED only one thread can do this. */ - state = (ptrace_reparented(p) && thread_group_leader(p)) ? - EXIT_TRACE : EXIT_DEAD; - if (cmpxchg(&p->exit_state, EXIT_ZOMBIE, state) != EXIT_ZOMBIE) + state = ((old_state == EXIT_TRACEE) && thread_group_leader(p)) ? + EXIT_TRACED : EXIT_DEAD; + if (cmpxchg(&p->exit_state, old_state, state) != old_state) return 0; /* * We own this thread, nobody else can reap it. @@ -1041,10 +1044,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p) read_unlock(&tasklist_lock); sched_annotate_sleep(); - /* - * Check thread_group_leader() to exclude the traced sub-threads. - */ - if (state == EXIT_DEAD && thread_group_leader(p)) { + if (old_state == EXIT_ZOMBIE) { struct signal_struct *sig = p->signal; struct signal_struct *psig = current->signal; unsigned long maxrss; @@ -1132,7 +1132,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p) if (!retval) retval = pid; - if (state == EXIT_TRACE) { + if (state == EXIT_TRACED) { write_lock_irq(&tasklist_lock); /* We dropped tasklist, ptracer could die and untrace */ ptrace_unlink(p); @@ -1335,8 +1335,7 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace, { /* * We can race with wait_task_zombie() from another thread. - * Ensure that EXIT_ZOMBIE -> EXIT_DEAD/EXIT_TRACE transition - * can't confuse the checks below. + * Ensure that exit_state transition can't confuse the checks below. */ int exit_state = ACCESS_ONCE(p->exit_state); int ret; @@ -1349,11 +1348,8 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace, return ret; /* zombie child process? */ - if ((exit_state == EXIT_ZOMBIE) && - !ptrace_reparented(p) && - thread_group_leader(p) && - thread_group_empty(p)) - return wait_task_zombie(wo, p); + if ((exit_state == EXIT_ZOMBIE) && thread_group_empty(p)) + return wait_task_zombie(wo, exit_state, p); /* * A zombie ptracee that is not a child of it's ptracer's @@ -1361,11 +1357,10 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace, * and reaping will be cascaded to the real parent when the * ptracer detaches. */ - if ((exit_state == EXIT_ZOMBIE) && ptrace && - (!thread_group_leader(p) || ptrace_reparented(p))) - return wait_task_zombie(wo, p); + if ((exit_state == EXIT_TRACEE) && ptrace) + return wait_task_zombie(wo, exit_state, p); - if (unlikely(exit_state == EXIT_TRACE)) { + if (unlikely(exit_state == EXIT_TRACED)) { /* * ptrace == 0 means we are the natural parent. In this case * we should clear notask_error, debugger will notify us. diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 490333db9e21..003567a615f9 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -497,27 +497,30 @@ static int ignoring_children(struct sighand_struct *sigh) */ static bool __exit_ptrace(struct task_struct *tracer, struct task_struct *p) { - bool dead; + int state = p->exit_state; __ptrace_unlink(p); - if (p->exit_state != EXIT_ZOMBIE) - return false; - - dead = !thread_group_leader(p); - - if (!dead && thread_group_empty(p)) { - if (!same_thread_group(p->real_parent, tracer)) - dead = do_notify_parent(p, p->exit_signal); - else if (ignoring_children(tracer->sighand)) { + if (state == EXIT_ZOMBIE) { + /* Honor the parents request to autoreap children */ + if (thread_group_empty(p) && + ignoring_children(tracer->sighand)) { + state = EXIT_DEAD; __wake_up_parent(p, tracer); - dead = true; + } + } + else if (state == EXIT_TRACEE) { + state = EXIT_DEAD; + if (thread_group_leader(p)) { + state = EXIT_ZOMBIE; + if (thread_group_empty(p) && + do_notify_parent(p, p->exit_signal)) + state = EXIT_DEAD; } } /* Mark it as in the process of being reaped. */ - if (dead) - p->exit_state = EXIT_DEAD; - return dead; + p->exit_state = state; + return state == EXIT_DEAD; } static int ptrace_detach(struct task_struct *child, unsigned int data) -- 2.10.1