Make the interrupt handler mp-asfe. Serialize the reception part of
genet_intr() interrupt handler and genet_rxtick() timeout handler with
`sc_mtx' mutex. The transmission part has nothing to do.

Running this on couple RPI4s without issues for a couple of days.

Index: sys/dev/acpi/if_bse_acpi.c
===================================================================
RCS file: /cvs/src/sys/dev/acpi/if_bse_acpi.c,v
diff -u -p -r1.6 if_bse_acpi.c
--- sys/dev/acpi/if_bse_acpi.c	6 Apr 2022 18:59:27 -0000	1.6
+++ sys/dev/acpi/if_bse_acpi.c	13 Feb 2026 17:15:12 -0000
@@ -90,7 +90,7 @@ bse_acpi_attach(struct device *parent, s
 	}
 
 	sc->sc.sc_ih = acpi_intr_establish(aaa->aaa_irq[0],
-	    aaa->aaa_irq_flags[0], IPL_NET, genet_intr,
+	    aaa->aaa_irq_flags[0], IPL_NET | IPL_MPSAFE, genet_intr,
 	    sc, sc->sc.sc_dev.dv_xname);
 	if (sc->sc.sc_ih == NULL) {
 		printf(": can't establish interrupt\n");
Index: sys/dev/fdt/if_bse_fdt.c
===================================================================
RCS file: /cvs/src/sys/dev/fdt/if_bse_fdt.c,v
diff -u -p -r1.2 if_bse_fdt.c
--- sys/dev/fdt/if_bse_fdt.c	6 Apr 2022 18:59:28 -0000	1.2
+++ sys/dev/fdt/if_bse_fdt.c	13 Feb 2026 17:15:12 -0000
@@ -72,7 +72,7 @@ bse_fdt_attach(struct device *parent, st
 		return;
 	}
 
-	sc->sc_ih = fdt_intr_establish(faa->fa_node, IPL_NET,
+	sc->sc_ih = fdt_intr_establish(faa->fa_node, IPL_NET | IPL_MPSAFE,
 	    genet_intr, sc, sc->sc_dev.dv_xname);
 	if (sc->sc_ih == NULL) {
 		printf(": can't establish interrupt\n");
Index: sys/dev/ic/bcmgenet.c
===================================================================
RCS file: /cvs/src/sys/dev/ic/bcmgenet.c,v
diff -u -p -r1.12 bcmgenet.c
--- sys/dev/ic/bcmgenet.c	24 Jan 2026 05:33:11 -0000	1.12
+++ sys/dev/ic/bcmgenet.c	13 Feb 2026 17:15:12 -0000
@@ -345,7 +345,11 @@ genet_fill_rx_ring(struct genet_softc *s
 void
 genet_rxtick(void *arg)
 {
-	genet_fill_rx_ring(arg, GENET_DMA_DEFAULT_QUEUE);
+	struct genet_softc *sc = arg;
+
+	mtx_enter(&sc->sc_mtx);
+	genet_fill_rx_ring(sc, GENET_DMA_DEFAULT_QUEUE);
+	mtx_leave(&sc->sc_mtx);
 }
 
 void
@@ -822,8 +826,11 @@ genet_intr(void *arg)
 	val &= ~RD4(sc, GENET_INTRL2_CPU_STAT_MASK);
 	WR4(sc, GENET_INTRL2_CPU_CLEAR, val);
 
-	if (val & GENET_IRQ_RXDMA_DONE)
+	if (val & GENET_IRQ_RXDMA_DONE) {
+		mtx_enter(&sc->sc_mtx);
 		genet_rxintr(sc, GENET_DMA_DEFAULT_QUEUE);
+		mtx_leave(&sc->sc_mtx);
+	}
 
 	if (val & GENET_IRQ_TXDMA_DONE) {
 		genet_txintr(sc, GENET_DMA_DEFAULT_QUEUE);
@@ -952,6 +959,7 @@ genet_attach(struct genet_softc *sc)
 		return EINVAL;
 	}
 
+	mtx_init(&sc->sc_mtx, IPL_NET);
 	timeout_set(&sc->sc_stat_ch, genet_tick, sc);
 	timeout_set(&sc->sc_rxto, genet_rxtick, sc);
 
Index: sys/dev/ic/bcmgenetvar.h
===================================================================
RCS file: /cvs/src/sys/dev/ic/bcmgenetvar.h,v
diff -u -p -r1.2 bcmgenetvar.h
--- sys/dev/ic/bcmgenetvar.h	15 Jan 2026 03:12:49 -0000	1.2
+++ sys/dev/ic/bcmgenetvar.h	13 Feb 2026 17:15:12 -0000
@@ -74,6 +74,7 @@ struct genet_softc {
 	struct genet_ring	sc_rx;
 	struct if_rxring	sc_rx_ring;
 	struct timeout		sc_rxto;
+	struct mutex		sc_mtx;
 };
 
 int	genet_attach(struct genet_softc *);