From b5bf9a90bbebffba888c9144c5a8a10317b04064 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 30 Apr 2018 14:51:01 +0200 Subject: sched/core: Introduce set_special_state() Gaurav reported a perceived problem with TASK_PARKED, which turned out to be a broken wait-loop pattern in __kthread_parkme(), but the reported issue can (and does) in fact happen for states that do not do condition based sleeps. When the 'current->state = TASK_RUNNING' store of a previous (concurrent) try_to_wake_up() collides with the setting of a 'special' sleep state, we can loose the sleep state. Normal condition based wait-loops are immune to this problem, but for sleep states that are not condition based are subject to this problem. There already is a fix for TASK_DEAD. Abstract that and also apply it to TASK_STOPPED and TASK_TRACED, both of which are also without condition based wait-loop. Reported-by: Gaurav Kohli Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Oleg Nesterov Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- kernel/signal.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) (limited to 'kernel/signal.c') diff --git a/kernel/signal.c b/kernel/signal.c index d4ccea599692..9c33163a6165 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1961,14 +1961,27 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info) return; } + set_special_state(TASK_TRACED); + /* * We're committing to trapping. TRACED should be visible before * TRAPPING is cleared; otherwise, the tracer might fail do_wait(). * Also, transition to TRACED and updates to ->jobctl should be * atomic with respect to siglock and should be done after the arch * hook as siglock is released and regrabbed across it. + * + * TRACER TRACEE + * + * ptrace_attach() + * [L] wait_on_bit(JOBCTL_TRAPPING) [S] set_special_state(TRACED) + * do_wait() + * set_current_state() smp_wmb(); + * ptrace_do_wait() + * wait_task_stopped() + * task_stopped_code() + * [L] task_is_traced() [S] task_clear_jobctl_trapping(); */ - set_current_state(TASK_TRACED); + smp_wmb(); current->last_siginfo = info; current->exit_code = exit_code; @@ -2176,7 +2189,7 @@ static bool do_signal_stop(int signr) if (task_participate_group_stop(current)) notify = CLD_STOPPED; - __set_current_state(TASK_STOPPED); + set_special_state(TASK_STOPPED); spin_unlock_irq(¤t->sighand->siglock); /* -- cgit v1.2.3