The patch titled
do_wait: fix waiting for the group stop with the dead leader
has been added to the -mm tree. Its filename is
do_wait-fix-waiting-for-the-group-stop-with-the-dead-leader.patch
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------------------------------------------------------
Subject: do_wait: fix waiting for the group stop with the dead leader
From: Oleg Nesterov <oleg@xxxxxxxxxx>
do_wait(WSTOPPED) assumes that p->state must be == TASK_STOPPED, this is
not true if the leader is already dead. Check SIGNAL_STOP_STOPPED instead
and use signal->group_exit_code.
Trivial test-case:
void *tfunc(void *arg)
{
pause();
return NULL;
}
int main(void)
{
pthread_t thr;
pthread_create(&thr, NULL, tfunc, NULL);
pthread_exit(NULL);
return 0;
}
It doesn't react to ^Z (and then to ^C or ^\). The task is stopped, but
bash can't see this.
The bug is very old, and it was reported multiple times. This patch was sent
more than a year ago (http://marc.info/?t=119713920000003) but it was ignored.
This change also fixes other oddities (but not all) in this area. For
example, before this patch:
$ sleep 100
^Z
[1]+ Stopped sleep 100
$ strace -p `pidof sleep`
Process 11442 attached - interrupt to quit
strace hangs in do_wait(), because ->exit_code was already consumed by
bash. After this patch, strace happily proceeds:
--- SIGTSTP (Stopped) @ 0 (0) ---
restart_syscall(<... resuming interrupted call ...>
To me, this looks much more "natural" and correct.
Another example. Let's suppose we have the main thread M and sub-thread
T, the process is stopped, and its parent did wait(WSTOPPED). Now we can
ptrace T but not M. This looks at least strange to me.
Imho, do_wait() should not confuse the per-thread ptrace stops with the
per-process job control stops.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Jan Kratochvil <jan.kratochvil@xxxxxxxxxx>
Cc: Kaz Kylheku <kkylheku@xxxxxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: Ulrich Drepper <drepper@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)
diff -puN kernel/exit.c~do_wait-fix-waiting-for-the-group-stop-with-the-dead-leader kernel/exit.c
--- a/kernel/exit.c~do_wait-fix-waiting-for-the-group-stop-with-the-dead-leader
+++ a/kernel/exit.c
@@ -1427,6 +1427,18 @@ static int wait_task_zombie(struct task_
return retval;
}
+static int *task_stopped_code(struct task_struct *p, bool ptrace)
+{
+ if (ptrace) {
+ if (task_is_stopped_or_traced(p))
+ return &p->exit_code;
+ } else {
+ if (p->signal->flags & SIGNAL_STOP_STOPPED)
+ return &p->signal->group_exit_code;
+ }
+ return NULL;
+}
+
/*
* Handle sys_wait4 work for one task in state TASK_STOPPED. We hold
* read_lock(&tasklist_lock) on entry. If we return zero, we still hold
@@ -1437,7 +1449,7 @@ static int wait_task_stopped(int ptrace,
int options, struct siginfo __user *infop,
int __user *stat_addr, struct rusage __user *ru)
{
- int retval, exit_code, why;
+ int retval, exit_code, *p_code, why;
uid_t uid = 0; /* unneeded, required by compiler */
pid_t pid;
@@ -1447,22 +1459,16 @@ static int wait_task_stopped(int ptrace,
exit_code = 0;
spin_lock_irq(&p->sighand->siglock);
- if (unlikely(!task_is_stopped_or_traced(p)))
- goto unlock_sig;
-
- if (!ptrace && p->signal->group_stop_count > 0)
- /*
- * A group stop is in progress and this is the group leader.
- * We won't report until all threads have stopped.
- */
+ p_code = task_stopped_code(p, ptrace);
+ if (unlikely(!p_code))
goto unlock_sig;
- exit_code = p->exit_code;
+ exit_code = *p_code;
if (!exit_code)
goto unlock_sig;
if (!unlikely(options & WNOWAIT))
- p->exit_code = 0;
+ *p_code = 0;
/* don't need the RCU readlock here as we're holding a spinlock */
uid = __task_cred(p)->uid;
@@ -1618,7 +1624,7 @@ static int wait_consider_task(struct tas
*/
*notask_error = 0;
- if (task_is_stopped_or_traced(p))
+ if (task_stopped_code(p, ptrace))
return wait_task_stopped(ptrace, p, options,
infop, stat_addr, ru);
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
linux-next.patch
pipe_rdwr_fasync-fix-the-error-handling-to-prevent-the-leak-crash.patch
get_mm_hiwater_xxx-trivial-s-define-inline.patch
getrusage-fill-ru_maxrss-value.patch
do_wait-fix-waiting-for-the-group-stop-with-the-dead-leader.patch
ptrace-kill-__ptrace_detach-fix-exit_state-check.patch
ptrace-simplify-ptrace_exit-ignoring_children-path.patch
ptrace-simplify-ptrace_exit-ignoring_children-pathpatch-fix.patch
ptrace-reintroduce-__ptrace_detach-as-a-callee-of-ptrace_exit.patch
ptrace-reintroduce-__ptrace_detach-as-a-callee-of-ptrace_exit-fix.patch
ptrace-fix-possible-zombie-leak-on-ptrace_detach.patch
reparent_thread-dont-call-kill_orphaned_pgrp-if-task_detached.patch
reparent_thread-fix-the-is-it-traced-check.patch
reparent_thread-fix-a-zombie-leak-if-sbin-init-ignores-sigchld.patch
forget_original_parent-split-out-the-un-ptrace-part.patch
forget_original_parent-do-not-abuse-child-ptrace_entry.patch
forget_original_parent-do-not-abuse-child-ptrace_entry-fix.patch
move-exit_ptrace-from-forget_original_parent-to-do_exit.patch
reparent-untrace-do-nothing-if-no-childs-tracees.patch
tracehook_notify_death-use-task_detached-helper.patch
workqueue-avoid-recursion-in-run_workqueue.patch
kthreads-move-sched-realeted-initialization-from-kthreadd-context.patch
kthreads-simplify-the-startup-synchronization.patch
kthreads-rework-kthread_stop.patch
kthreads-simplify-migration_thread-exit-path.patch
pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu.patch
pids-document-task_pgrp-task_session-is-not-safe-without-tasklist-rcu-fix.patch
pids-improve-get_task_pid-to-fix-the-unsafe-sys_wait4-task_pgrp.patch
pids-refactor-vnr-nr_ns-helpers-to-make-them-safe.patch
pids-kill-now-unused-signal_struct-__pgrp-__session-and-friends.patch
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