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>
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@ -62,6 +62,7 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
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static int signals_enabled;
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static unsigned int signals_pending;
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static unsigned int signals_active = 0;
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void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
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{
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@ -101,7 +102,12 @@ void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
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block_signals();
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signals_active |= SIGALRM_MASK;
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timer_real_alarm_handler(mc);
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signals_active &= ~SIGALRM_MASK;
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set_signals(enabled);
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}
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@ -286,8 +292,16 @@ void unblock_signals(void)
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if (save_pending & SIGIO_MASK)
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sig_handler_common(SIGIO, NULL, NULL);
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if (save_pending & SIGALRM_MASK)
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/* Do not reenter the handler */
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if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
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timer_real_alarm_handler(NULL);
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/* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
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if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
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return;
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}
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}
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