Fix possible deadlock on SMP stop_this_cpu

Do not use printk on the running thread after it has been sent
the INIT IPI, execution may halt with console spinlock held.

Change-Id: I64608935ea740fb827fa0307442f3fb102de7a08
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/776
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Rudolf Marek <r.marek@assembler.cz>

diff --git a/src/cpu/x86/lapic/lapic_cpu_init.c b/src/cpu/x86/lapic/lapic_cpu_init.c
index fc22ea4adf9a9e7fd5b8996475f485b518a283b6..2e2bb0632c3883fbea87315964089aa96d047bbc 100644 (file)
--- a/src/cpu/x86/lapic/lapic_cpu_init.c
+++ b/src/cpu/x86/lapic/lapic_cpu_init.c
@@ -277,6 +277,19 @@ int start_cpu(device_t cpu)
 }
 
 #if CONFIG_AP_IN_SIPI_WAIT == 1
+
+/**
+ * Sending INIT IPI to self is equivalent of asserting #INIT with a bit of delay.
+ * An undefined number of instruction cycles will complete. All global locks
+ * must be released before INIT IPI and no printk is allowed after this.
+ * De-asserting INIT IPI is a no-op on later Intel CPUs.
+ *
+ * If you set DEBUG_HALT_SELF to 1, printk's after INIT IPI are enabled
+ * but running thread may halt without releasing the lock and effectively
+ * deadlock other CPUs.
+ */
+#define DEBUG_HALT_SELF 0
+
 /**
  * Normally this function is defined in lapic.h as an always inline function
  * that just keeps the CPU in a hlt() loop. This does not work on all CPUs.
@@ -298,38 +311,46 @@ void stop_this_cpu(void)
        lapic_write_around(LAPIC_ICR, LAPIC_INT_LEVELTRIG | LAPIC_INT_ASSERT | LAPIC_DM_INIT);
 
        /* wait for the ipi send to finish */
-#if 0
-       // When these two printk(BIOS_SPEW, ...) calls are not removed, the
-       // machine will hang when log level is SPEW. Why?
+#if DEBUG_HALT_SELF
        printk(BIOS_SPEW, "Waiting for send to finish...\n");
 #endif
        timeout = 0;
        do {
-#if 0
+#if DEBUG_HALT_SELF
                printk(BIOS_SPEW, "+");
 #endif
                udelay(100);
                send_status = lapic_read(LAPIC_ICR) & LAPIC_ICR_BUSY;
        } while (send_status && (timeout++ < 1000));
        if (timeout >= 1000) {
+#if DEBUG_HALT_SELF
                printk(BIOS_ERR, "timed out\n");
+#endif
        }
        mdelay(10);
 
+#if DEBUG_HALT_SELF
        printk(BIOS_SPEW, "Deasserting INIT.\n");
+#endif
        /* Deassert the LAPIC INIT */
        lapic_write_around(LAPIC_ICR2, SET_LAPIC_DEST_FIELD(id));
        lapic_write_around(LAPIC_ICR, LAPIC_INT_LEVELTRIG | LAPIC_DM_INIT);
 
+#if DEBUG_HALT_SELF
        printk(BIOS_SPEW, "Waiting for send to finish...\n");
+#endif
        timeout = 0;
        do {
+#if DEBUG_HALT_SELF
                printk(BIOS_SPEW, "+");
+#endif
                udelay(100);
                send_status = lapic_read(LAPIC_ICR) & LAPIC_ICR_BUSY;
        } while (send_status && (timeout++ < 1000));
        if (timeout >= 1000) {
+#if DEBUG_HALT_SELF
                printk(BIOS_ERR, "timed out\n");
+#endif
        }
 
        while(1) {