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
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------------------------------------------------------
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
--
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