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authorAnton Ivanov <aivanov@brocade.com>2015-12-21 11:28:02 +0000
committerRichard Weinberger <richard@nod.at>2016-01-10 21:49:47 +0100
commitd5e3f5cbe5cee7fe6da26566559a978547179b37 (patch)
tree7f40e2da3a070e811a412865ffbf5c317844e257 /arch/um
parent0754fb298f2f2719f0393491d010d46cfb25d043 (diff)
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>
Diffstat (limited to 'arch/um')
-rw-r--r--arch/um/os-Linux/signal.c16
1 files changed, 15 insertions, 1 deletions
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;
+
}
}