From d5e3f5cbe5cee7fe6da26566559a978547179b37 Mon Sep 17 00:00:00 2001 From: Anton Ivanov Date: Mon, 21 Dec 2015 11:28:02 +0000 Subject: [PATCH] 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 Signed-off-by: Richard Weinberger --- arch/um/os-Linux/signal.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c index c211153ca69a..7801666514ed 100644 --- a/arch/um/os-Linux/signal.c +++ b/arch/um/os-Linux/signal.c @@ -62,6 +62,7 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc) 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 @@ void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc) block_signals(); + signals_active |= SIGALRM_MASK; + timer_real_alarm_handler(mc); + + signals_active &= ~SIGALRM_MASK; + set_signals(enabled); } @@ -286,8 +292,16 @@ void unblock_signals(void) 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; + } }