um: Prevent IRQ handler reentrancy (d5e3f5cb) · Commits · 戴 / test

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>

arch/um/os-Linux/signal.c

+15 −1

Original line number	Diff line number	Diff line
		@@ -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;

		}
		}

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