From 707e59ba494372a90d245f18b0c78982caa88e48 Mon Sep 17 00:00:00 2001 From: Ross Lagerwall Date: Fri, 22 Apr 2016 13:05:31 +0100 Subject: [PATCH] xen/qspinlock: Don't kick CPU if IRQ is not initialized The following commit: 1fb3a8b2cfb2 ("xen/spinlock: Fix locking path engaging too soon under PVHVM.") ... moved the initalization of the kicker interrupt until after native_cpu_up() is called. However, when using qspinlocks, a CPU may try to kick another CPU that is spinning (because it has not yet initialized its kicker interrupt), resulting in the following crash during boot: kernel BUG at /build/linux-Ay7j_C/linux-4.4.0/drivers/xen/events/events_base.c:1210! invalid opcode: 0000 [#1] SMP ... RIP: 0010:[] [] xen_send_IPI_one+0x59/0x60 ... Call Trace: [] xen_qlock_kick+0xe/0x10 [] __pv_queued_spin_unlock+0xb2/0xf0 [] ? __raw_callee_save___pv_queued_spin_unlock+0x11/0x20 [] ? check_tsc_warp+0x76/0x150 [] check_tsc_sync_source+0x96/0x160 [] native_cpu_up+0x3d8/0x9f0 [] xen_hvm_cpu_up+0x35/0x80 [] _cpu_up+0x13c/0x180 [] cpu_up+0x7a/0xa0 [] smp_init+0x7f/0x81 [] kernel_init_freeable+0xef/0x212 [] ? rest_init+0x80/0x80 [] kernel_init+0xe/0xe0 [] ret_from_fork+0x3f/0x70 [] ? rest_init+0x80/0x80 To fix this, only send the kick if the target CPU's interrupt has been initialized. This check isn't racy, because the target is waiting for the spinlock, so it won't have initialized the interrupt in the meantime. Signed-off-by: Ross Lagerwall Reviewed-by: Boris Ostrovsky Cc: David Vrabel Cc: Juergen Gross Cc: Konrad Rzeszutek Wilk Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Cc: xen-devel@lists.xenproject.org Signed-off-by: Ingo Molnar --- arch/x86/xen/spinlock.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index 9e2ba5c..f42e78d 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -27,6 +27,12 @@ static bool xen_pvspin = true; static void xen_qlock_kick(int cpu) { + int irq = per_cpu(lock_kicker_irq, cpu); + + /* Don't kick if the target's kicker interrupt is not initialized. */ + if (irq == -1) + return; + xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR); } -- 2.7.4