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authorPeter Zijlstra <peterz@infradead.org>2018-04-30 14:51:01 +0200
committerIngo Molnar <mingo@kernel.org>2018-05-04 07:54:54 +0200
commitb5bf9a90bbebffba888c9144c5a8a10317b04064 (patch)
tree4c059f0785c26ca66df0009544a23b68f7228be3 /kernel/signal.c
parent85f1abe0019fcb3ea10df7029056cf42702283a8 (diff)
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 <gkohli@codeaurora.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c17
1 files changed, 15 insertions, 2 deletions
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(&current->sighand->siglock);
/*