The patch titled ptrace: __ptrace_detach: do __wake_up_parent() if we reap the tracee has been added to the -mm tree. Its filename is ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: ptrace: __ptrace_detach: do __wake_up_parent() if we reap the tracee From: Oleg Nesterov <oleg@xxxxxxxxxx> The bug is old, it wasn't cause by recent changes. Test case: static void *tfunc(void *arg) { int pid = (long)arg; assert(ptrace(PTRACE_ATTACH, pid, NULL, NULL) == 0); kill(pid, SIGKILL); sleep(1); return NULL; } int main(void) { pthread_t th; long pid = fork(); if (!pid) pause(); signal(SIGCHLD, SIG_IGN); assert(pthread_create(&th, NULL, tfunc, (void*)pid) == 0); int r = waitpid(-1, NULL, __WNOTHREAD); printf("waitpid: %d %m\n", r); return 0; } Before the patch this program hangs, after this patch waitpid() correctly fails with errno == -ECHILD. The problem is, __ptrace_detach() reaps the EXIT_ZOMBIE tracee if its ->real_parent is our sub-thread and we ignore SIGCHLD. But in this case we should wake up other threads which can sleep in do_wait(). Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Roland McGrath <roland@xxxxxxxxxx> Cc: Vitaly Mayatskikh <vmayatsk@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/sched.h | 1 + kernel/exit.c | 5 +++++ kernel/ptrace.c | 11 +++++++---- kernel/signal.c | 9 --------- 4 files changed, 13 insertions(+), 13 deletions(-) diff -puN include/linux/sched.h~ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee include/linux/sched.h --- a/include/linux/sched.h~ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee +++ a/include/linux/sched.h @@ -1983,6 +1983,7 @@ extern int kill_pgrp(struct pid *pid, in extern int kill_pid(struct pid *pid, int sig, int priv); extern int kill_proc_info(int, struct siginfo *, pid_t); extern int do_notify_parent(struct task_struct *, int); +extern void __wake_up_parent(struct task_struct *p, struct task_struct *parent); extern void force_sig(int, struct task_struct *); extern void force_sig_specific(int, struct task_struct *); extern int send_sig(int, struct task_struct *, int); diff -puN kernel/exit.c~ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee kernel/exit.c --- a/kernel/exit.c~ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee +++ a/kernel/exit.c @@ -1571,6 +1571,11 @@ static int ptrace_do_wait(struct wait_op return 0; } +void __wake_up_parent(struct task_struct *p, struct task_struct *parent) +{ + wake_up_interruptible_sync(&parent->signal->wait_chldexit); +} + static long do_wait(struct wait_opts *wo) { DECLARE_WAITQUEUE(wait, current); diff -puN kernel/ptrace.c~ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee kernel/ptrace.c --- a/kernel/ptrace.c~ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee +++ a/kernel/ptrace.c @@ -266,9 +266,10 @@ static int ignoring_children(struct sigh * or self-reaping. Do notification now if it would have happened earlier. * If it should reap itself, return true. * - * If it's our own child, there is no notification to do. - * But if our normal children self-reap, then this child - * was prevented by ptrace and we must reap it now. + * If it's our own child, there is no notification to do. But if our normal + * children self-reap, then this child was prevented by ptrace and we must + * reap it now, in that case we must also wake up sub-threads sleeping in + * do_wait(). */ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p) { @@ -278,8 +279,10 @@ static bool __ptrace_detach(struct task_ if (!task_detached(p) && thread_group_empty(p)) { if (!same_thread_group(p->real_parent, tracer)) do_notify_parent(p, p->exit_signal); - else if (ignoring_children(tracer->sighand)) + else if (ignoring_children(tracer->sighand)) { + __wake_up_parent(p, tracer); p->exit_signal = -1; + } } if (task_detached(p)) { /* Mark it as in the process of being reaped. */ diff -puN kernel/signal.c~ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee kernel/signal.c --- a/kernel/signal.c~ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee +++ a/kernel/signal.c @@ -1383,15 +1383,6 @@ ret: } /* - * Wake up any threads in the parent blocked in wait* syscalls. - */ -static inline void __wake_up_parent(struct task_struct *p, - struct task_struct *parent) -{ - wake_up_interruptible_sync(&parent->signal->wait_chldexit); -} - -/* * Let a parent know about the death of a child. * For a stopped/continued status change, use do_notify_parent_cldstop instead. * _ Patches currently in -mm which might be from oleg@xxxxxxxxxx are linux-next.patch cred_guard_mutex-do-not-return-eintr-to-user-space.patch rework-fix-is_single_threaded.patch getrusage-fill-ru_maxrss-value.patch getrusage-fill-ru_maxrss-value-update.patch ptrace-__ptrace_detach-do-__wake_up_parent-if-we-reap-the-tracee.patch signals-tracehook_notify_jctl-change.patch utrace-core.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html