um: Prevent IRQ handler reentrancy
The existing IRQ handler design in UML does not prevent reentrancy
This is mitigated by fd-enable/fd-disable semantics for the IO
portion of the UML subsystem. The timer, however, can and is
re-entered resulting in very deep stack usage and occasional
stack exhaustion.
This patch prevents this by checking if there is a timer
interrupt in-flight before processing any pending timer interrupts.
Signed-off-by: Anton Ivanov <aivanov@brocade.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index c211153..7801666 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -62,6 +62,7 @@
static int signals_enabled;
static unsigned int signals_pending;
+static unsigned int signals_active = 0;
void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
{
@@ -101,7 +102,12 @@
block_signals();
+ signals_active |= SIGALRM_MASK;
+
timer_real_alarm_handler(mc);
+
+ signals_active &= ~SIGALRM_MASK;
+
set_signals(enabled);
}
@@ -286,8 +292,16 @@
if (save_pending & SIGIO_MASK)
sig_handler_common(SIGIO, NULL, NULL);
- if (save_pending & SIGALRM_MASK)
+ /* Do not reenter the handler */
+
+ if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
timer_real_alarm_handler(NULL);
+
+ /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
+
+ if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
+ return;
+
}
}
