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authorKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2013-08-13 11:47:21 -0400
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2013-09-09 12:06:16 -0400
commit1fb3a8b2cfb278f139d9ff7ca5fe06a65de64494 (patch)
treeafa04e3edf9b99e621593464dd9d1f027b19e4ff /arch/x86
parent65320fcedaa7affd1736cd7aa51f5e70b5c7e7f2 (diff)
downloadop-kernel-dev-1fb3a8b2cfb278f139d9ff7ca5fe06a65de64494.zip
op-kernel-dev-1fb3a8b2cfb278f139d9ff7ca5fe06a65de64494.tar.gz
xen/spinlock: Fix locking path engaging too soon under PVHVM.
The xen_lock_spinning has a check for the kicker interrupts and if it is not initialized it will spin normally (not enter the slowpath). But for PVHVM case we would initialize the kicker interrupt before the CPU came online. This meant that if the booting CPU used a spinlock and went in the slowpath - it would enter the slowpath and block forever. The forever part because during bootup: the spinlock would be taken _before_ the CPU sets itself to be online (more on this further), and we enter to poll on the event channel forever. The bootup CPU (see commit fc78d343fa74514f6fd117b5ef4cd27e4ac30236 "xen/smp: initialize IPI vectors before marking CPU online" for details) and the CPU that started the bootup consult the cpu_online_mask to determine whether the booting CPU should get an IPI. The booting CPU has to set itself in this mask via: set_cpu_online(smp_processor_id(), true); However, if the spinlock is taken before this (and it is) and it polls on an event channel - it will never be woken up as the kernel will never send an IPI to an offline CPU. Note that the PVHVM logic in sending IPIs is using the HVM path which has numerous checks using the cpu_online_mask and cpu_active_mask. See above mention git commit for details. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/xen/enlighten.c1
-rw-r--r--arch/x86/xen/smp.c9
2 files changed, 9 insertions, 1 deletions
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 15939e8..f091c80 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1692,7 +1692,6 @@ static int xen_hvm_cpu_notify(struct notifier_block *self, unsigned long action,
case CPU_UP_PREPARE:
xen_vcpu_setup(cpu);
if (xen_have_vector_callback) {
- xen_init_lock_cpu(cpu);
if (xen_feature(XENFEAT_hvm_safe_pvclock))
xen_setup_timer(cpu);
}
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 9235842..c21b825 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -709,6 +709,15 @@ static int xen_hvm_cpu_up(unsigned int cpu, struct task_struct *tidle)
WARN_ON(rc);
if (!rc)
rc = native_cpu_up(cpu, tidle);
+
+ /*
+ * We must initialize the slowpath CPU kicker _after_ the native
+ * path has executed. If we initialized it before none of the
+ * unlocker IPI kicks would reach the booting CPU as the booting
+ * CPU had not set itself 'online' in cpu_online_mask. That mask
+ * is checked when IPIs are sent (on HVM at least).
+ */
+ xen_init_lock_cpu(cpu);
return rc;
}
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