um: time-travel/signals: fix ndelay() in interrupt

We should be able to ndelay() from any context, even from an
interrupt context! However, this is broken (not functionally,
but locking-wise) in time-travel because we'll get into the
time-travel code and enable interrupts to handle messages on
other time-travel aware subsystems (only virtio for now).

Luckily, I've already reworked the time-travel aware signal
(interrupt) delivery for suspend/resume to have a time travel
handler, which runs directly in the context of the signal and
not from the Linux interrupt.

In order to fix this time-travel issue then, we need to do a
few things:

 1) rework the signal handling code to call time-travel handlers
    (only) if interrupts are disabled but signals aren't blocked,
    instead of marking it only pending there. This is needed to
    not deadlock other communication.
 2) rework time-travel to not enable interrupts while it's
    waiting for a message;
 3) rework time-travel to not (just) disable interrupts but
    rather block signals at a lower level while it needs them
    disabled for communicating with the controller.

Finally, since now we can actually spend even virtual time
in interrupts-disabled sections, the delay warning when we
deliver a time-travel delayed interrupt is no longer valid,
things can (and should) now get delayed.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 51 insertions, 4 deletions

diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 8c9d162e6c51..1d501acb22ee 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -18,6 +18,7 @@
 #include <sysdep/mcontext.h>
 #include <um_malloc.h>
 #include <sys/ucontext.h>
+#include <timetravel.h>
 
 void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
 	[SIGTRAP]	= relay_signal,
@@ -63,16 +64,29 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
 #define SIGALRM_MASK (1 << SIGALRM_BIT)
 
 int signals_enabled;
+#ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT
+static int signals_blocked;
+#else
+#define signals_blocked false
+#endif
 static unsigned int signals_pending;
 static unsigned int signals_active = 0;
 
 void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
 {
-	int enabled;
+	int enabled = signals_enabled;
 
-	enabled = signals_enabled;
-	if (!enabled && (sig == SIGIO)) {
-		signals_pending |= SIGIO_MASK;
+	if ((signals_blocked || !enabled) && (sig == SIGIO)) {
+		/*
+		 * In TT_MODE_EXTERNAL, need to still call time-travel
+		 * handlers unless signals are also blocked for the
+		 * external time message processing. This will mark
+		 * signals_pending by itself (only if necessary.)
+		 */
+		if (!signals_blocked && time_travel_mode == TT_MODE_EXTERNAL)
+			sigio_run_timetravel_handlers();
+		else
+			signals_pending |= SIGIO_MASK;
 		return;
 	}
 
@@ -363,6 +377,39 @@ int set_signals_trace(int enable)
 	return ret;
 }
 
+#ifdef UML_CONFIG_UML_TIME_TRAVEL_SUPPORT
+void mark_sigio_pending(void)
+{
+	signals_pending |= SIGIO_MASK;
+}
+
+void block_signals_hard(void)
+{
+	if (signals_blocked)
+		return;
+	signals_blocked = 1;
+	barrier();
+}
+
+void unblock_signals_hard(void)
+{
+	if (!signals_blocked)
+		return;
+	/* Must be set to 0 before we check the pending bits etc. */
+	signals_blocked = 0;
+	barrier();
+
+	if (signals_pending && signals_enabled) {
+		/* this is a bit inefficient, but that's not really important */
+		block_signals();
+		unblock_signals();
+	} else if (signals_pending & SIGIO_MASK) {
+		/* we need to run time-travel handlers even if not enabled */
+		sigio_run_timetravel_handlers();
+	}
+}
+#endif
+
 int os_is_signal_stack(void)
 {
 	stack_t ss;