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Message-ID: <20151105201740.GA15785@redhat.com>
Date: Thu, 5 Nov 2015 21:17:40 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
Dmitry Vyukov <dvyukov@...gle.com>
Cc: Roland McGrath <roland@...k.frob.com>, amanieu@...il.com,
pmoore@...hat.com, Ingo Molnar <mingo@...nel.org>,
vdavydov@...allels.com, qiaowei.ren@...el.com, dave@...olabs.net,
palmer@...belt.com, syzkaller <syzkaller@...glegroups.com>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/3] signal: kill the obsolete SIGNAL_UNKILLABLE check
in complete_signal()
complete_signal() checks SIGNAL_UNKILLABLE before it starts to destroy the
thread group, today this is unnecessary and even not 100% correct.
After the previous change we can rely on sig_task_ignored(); sig_fatal(sig)
&& SIGNAL_UNKILLABLE can only be true if we actually want to kill this task.
And it does not look right. fatal_signal_pending() should always imply that
the whole thread group (except ->group_exit_task if it is not NULL) is killed,
this check breaks the rule.
This explains WARN_ON(!JOBCTL_STOP_PENDING) in task_participate_group_stop()
triggered by the test-case from Dmitry:
int main()
{
int pid = 1;
ptrace(PTRACE_ATTACH, pid, 0, 0);
ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_EXITKILL);
sleep(1);
return 0;
}
do_signal_stop()->signal_group_exit() returns false because SIGNAL_GROUP_EXIT
is not set, but task_set_jobctl_pending() checks fatal_signal_pending() and
does not set JOBCTL_STOP_PENDING.
The test-case above needs root and (correctly) crashes the kernel, but we can
trigger the same warning inside the container or using another test-case:
static int init(void *arg)
{
for (;;)
pause();
}
int main(void)
{
char stack[16 * 1024];
for (;;) {
int pid = clone(init, stack + sizeof(stack)/2,
CLONE_NEWPID | SIGCHLD, NULL);
assert(pid > 0);
assert(ptrace(PTRACE_ATTACH, pid, 0, 0) == 0);
assert(waitpid(-1, NULL, WSTOPPED) == pid);
assert(ptrace(PTRACE_DETACH, pid, 0, SIGSTOP) == 0);
assert(syscall(__NR_tkill, pid, SIGKILL) == 0);
assert(pid == wait(NULL));
}
}
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
kernel/signal.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 87209e5..7e9f6fa 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -914,7 +914,7 @@ static void complete_signal(int sig, struct task_struct *p, int group)
* then start taking the whole group down immediately.
*/
if (sig_fatal(p, sig) &&
- !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) &&
+ !(signal->flags & SIGNAL_GROUP_EXIT) &&
!sigismember(&t->real_blocked, sig) &&
(sig == SIGKILL || !t->ptrace)) {
/*
--
1.5.5.1
--
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