Patch "xen/qspinlock: Don't kick CPU if IRQ is not initialized" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    xen/qspinlock: Don't kick CPU if IRQ is not initialized

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     xen-qspinlock-don-t-kick-cpu-if-irq-is-not-initialized.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 707e59ba494372a90d245f18b0c78982caa88e48 Mon Sep 17 00:00:00 2001
From: Ross Lagerwall <ross.lagerwall@citrix.com>
Date: Fri, 22 Apr 2016 13:05:31 +0100
Subject: xen/qspinlock: Don't kick CPU if IRQ is not initialized

From: Ross Lagerwall <ross.lagerwall@citrix.com>

commit 707e59ba494372a90d245f18b0c78982caa88e48 upstream.

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:[<ffffffff814c97c9>]  [<ffffffff814c97c9>] xen_send_IPI_one+0x59/0x60
  ...
  Call Trace:
   [<ffffffff8102be9e>] xen_qlock_kick+0xe/0x10
   [<ffffffff810cabc2>] __pv_queued_spin_unlock+0xb2/0xf0
   [<ffffffff810ca6d1>] ? __raw_callee_save___pv_queued_spin_unlock+0x11/0x20
   [<ffffffff81052936>] ? check_tsc_warp+0x76/0x150
   [<ffffffff81052aa6>] check_tsc_sync_source+0x96/0x160
   [<ffffffff81051e28>] native_cpu_up+0x3d8/0x9f0
   [<ffffffff8102b315>] xen_hvm_cpu_up+0x35/0x80
   [<ffffffff8108198c>] _cpu_up+0x13c/0x180
   [<ffffffff81081a4a>] cpu_up+0x7a/0xa0
   [<ffffffff81f80dfc>] smp_init+0x7f/0x81
   [<ffffffff81f5a121>] kernel_init_freeable+0xef/0x212
   [<ffffffff81817f30>] ? rest_init+0x80/0x80
   [<ffffffff81817f3e>] kernel_init+0xe/0xe0
   [<ffffffff8182488f>] ret_from_fork+0x3f/0x70
   [<ffffffff81817f30>] ? 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 <ross.lagerwall@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: xen-devel@lists.xenproject.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/xen/spinlock.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- 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);
 }
 


Patches currently in stable-queue which might be from ross.lagerwall@citrix.com are

queue-4.4/xen-qspinlock-don-t-kick-cpu-if-irq-is-not-initialized.patch