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authorTejun Heo <tj@kernel.org>2011-03-23 10:37:01 +0100
committerTejun Heo <tj@kernel.org>2011-03-23 10:37:01 +0100
commitceb6bd67f9b9db765e1c29405f26e8460391badd (patch)
treed4db6cfe58bf2d84bf6af8f1079619050f6c8adc /kernel/signal.c
parent62bcf9d992ecc19ea4f37ff57ee0b3333e3e843e (diff)
downloadlwn-ceb6bd67f9b9db765e1c29405f26e8460391badd.tar.gz
lwn-ceb6bd67f9b9db765e1c29405f26e8460391badd.zip
job control: Notify the real parent of job control events regardless of ptrace
With recent changes, job control and ptrace stopped states are properly separated and accessible to the real parent and the ptracer respectively; however, notifications of job control stopped/continued events to the real parent while ptraced are still missing. A ptracee participates in group stop in ptrace_stop() but the completion isn't notified. If participation results in completion of group stop, notify the real parent of the event. The ptrace and group stops are separate and can be handled as such. However, when the real parent and the ptracer are in the same thread group, only the ptrace stop event is visible through wait(2) and the duplicate notifications are different from the current behavior and are confusing. Suppress group stop notification in such cases. The continued state is shared between the real parent and the ptracer but is only meaningful to the real parent. Always notify the real parent and notify the ptracer too for backward compatibility. Similar to stop notification, if the real parent is the ptracer, suppress a duplicate notification. Test case follows. #include <stdio.h> #include <unistd.h> #include <time.h> #include <errno.h> #include <sys/types.h> #include <sys/ptrace.h> #include <sys/wait.h> int main(void) { const struct timespec ts100ms = { .tv_nsec = 100000000 }; pid_t tracee, tracer; siginfo_t si; int i; tracee = fork(); if (tracee == 0) { while (1) { printf("tracee: SIGSTOP\n"); raise(SIGSTOP); nanosleep(&ts100ms, NULL); printf("tracee: SIGCONT\n"); raise(SIGCONT); nanosleep(&ts100ms, NULL); } } waitid(P_PID, tracee, &si, WSTOPPED | WNOHANG | WNOWAIT); tracer = fork(); if (tracer == 0) { nanosleep(&ts100ms, NULL); ptrace(PTRACE_ATTACH, tracee, NULL, NULL); for (i = 0; i < 11; i++) { si.si_pid = 0; waitid(P_PID, tracee, &si, WSTOPPED); if (si.si_pid && si.si_code == CLD_TRAPPED) ptrace(PTRACE_CONT, tracee, NULL, (void *)(long)si.si_status); } printf("tracer: EXITING\n"); return 0; } while (1) { si.si_pid = 0; waitid(P_PID, tracee, &si, WSTOPPED | WCONTINUED | WEXITED); if (si.si_pid) printf("mommy : WAIT status=%02d code=%02d\n", si.si_status, si.si_code); } return 0; } Before this patch, while ptraced, the real parent doesn't get notifications for job control events, so although it can access those events, the later waitid(2) call never wakes up. tracee: SIGSTOP mommy : WAIT status=19 code=05 tracee: SIGCONT tracee: SIGSTOP tracee: SIGCONT tracee: SIGSTOP tracee: SIGCONT tracee: SIGSTOP tracer: EXITING mommy : WAIT status=19 code=05 ^C After this patch, it works as expected. tracee: SIGSTOP mommy : WAIT status=19 code=05 tracee: SIGCONT mommy : WAIT status=18 code=06 tracee: SIGSTOP mommy : WAIT status=19 code=05 tracee: SIGCONT mommy : WAIT status=18 code=06 tracee: SIGSTOP mommy : WAIT status=19 code=05 tracee: SIGCONT mommy : WAIT status=18 code=06 tracee: SIGSTOP tracer: EXITING mommy : WAIT status=19 code=05 ^C -v2: Oleg pointed out that * Group stop notification to the real parent should also happen when ptracer detach races with ptrace_stop(). * real_parent_is_ptracer() should be testing thread group equality not the task itself as wait(2) and stop/cont notifications are normally thread-group wide. Both issues are fixed accordingly. -v3: real_parent_is_ptracer() updated to test child->real_parent instead of child->group_leader->real_parent per Oleg's suggestion. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Oleg Nesterov <oleg@redhat.com>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c53
1 files changed, 50 insertions, 3 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index 9f10b246fd46..f65403da4101 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1694,6 +1694,15 @@ static int sigkill_pending(struct task_struct *tsk)
}
/*
+ * Test whether the target task of the usual cldstop notification - the
+ * real_parent of @child - is in the same group as the ptracer.
+ */
+static bool real_parent_is_ptracer(struct task_struct *child)
+{
+ return same_thread_group(child->parent, child->real_parent);
+}
+
+/*
* This must be called with current->sighand->siglock held.
*
* This should be the path for all ptrace stops.
@@ -1708,6 +1717,8 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
__releases(&current->sighand->siglock)
__acquires(&current->sighand->siglock)
{
+ bool gstop_done = false;
+
if (arch_ptrace_stop_needed(exit_code, info)) {
/*
* The arch code has something special to do before a
@@ -1735,7 +1746,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
* is entered - ignore it.
*/
if (why == CLD_STOPPED && (current->group_stop & GROUP_STOP_PENDING))
- task_participate_group_stop(current);
+ gstop_done = task_participate_group_stop(current);
current->last_siginfo = info;
current->exit_code = exit_code;
@@ -1757,7 +1768,20 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
spin_unlock_irq(&current->sighand->siglock);
read_lock(&tasklist_lock);
if (may_ptrace_stop()) {
- do_notify_parent_cldstop(current, task_ptrace(current), why);
+ /*
+ * Notify parents of the stop.
+ *
+ * While ptraced, there are two parents - the ptracer and
+ * the real_parent of the group_leader. The ptracer should
+ * know about every stop while the real parent is only
+ * interested in the completion of group stop. The states
+ * for the two don't interact with each other. Notify
+ * separately unless they're gonna be duplicates.
+ */
+ do_notify_parent_cldstop(current, true, why);
+ if (gstop_done && !real_parent_is_ptracer(current))
+ do_notify_parent_cldstop(current, false, why);
+
/*
* Don't want to allow preemption here, because
* sys_ptrace() needs this task to be inactive.
@@ -1772,7 +1796,16 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
/*
* By the time we got the lock, our tracer went away.
* Don't drop the lock yet, another tracer may come.
+ *
+ * If @gstop_done, the ptracer went away between group stop
+ * completion and here. During detach, it would have set
+ * GROUP_STOP_PENDING on us and we'll re-enter TASK_STOPPED
+ * in do_signal_stop() on return, so notifying the real
+ * parent of the group stop completion is enough.
*/
+ if (gstop_done)
+ do_notify_parent_cldstop(current, false, why);
+
__set_current_state(TASK_RUNNING);
if (clear_code)
current->exit_code = 0;
@@ -2017,10 +2050,24 @@ relock:
spin_unlock_irq(&sighand->siglock);
+ /*
+ * Notify the parent that we're continuing. This event is
+ * always per-process and doesn't make whole lot of sense
+ * for ptracers, who shouldn't consume the state via
+ * wait(2) either, but, for backward compatibility, notify
+ * the ptracer of the group leader too unless it's gonna be
+ * a duplicate.
+ */
read_lock(&tasklist_lock);
+
+ do_notify_parent_cldstop(current, false, why);
+
leader = current->group_leader;
- do_notify_parent_cldstop(leader, task_ptrace(leader), why);
+ if (task_ptrace(leader) && !real_parent_is_ptracer(leader))
+ do_notify_parent_cldstop(leader, true, why);
+
read_unlock(&tasklist_lock);
+
goto relock;
}