Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit d5e3f5cb authored by Anton Ivanov's avatar Anton Ivanov Committed by Richard Weinberger
Browse files

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: default avatarAnton Ivanov <aivanov@brocade.com>
Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
parent 0754fb29

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;



	}

}