New patch to review for coreboot: af24a61 Fix possible deadlock on SMP stop_this_cpu

[Kyösti Mälkki]

Kyösti Mälkki ([e-mail]) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/776

-gerrit

commit af24a610077c3bca7aa2e47bb0a05b4b1035f996
Author: Kyösti Mälkki 
Date:   Sun Mar 4 02:24:36 2012 +0200

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 
---
 src/cpu/x86/lapic/lapic_cpu_init.c |   29 +++++++++++++++++++++++++----
 1 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/cpu/x86/lapic/lapic_cpu_init.c b/src/cpu/x86/lapic/lapic_cpu_init.c
index fc22ea4..2e2bb06 100644
--- 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) {