[PATCH] PCI: hv: Fix a __local_bh_enable_ip warning in hv_compose_msi_msg()

[Dexuan Cui]

Commit de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in hv_compose_msi_msg()")
uses local_bh_disable()/enable(), because hv_pci_onchannelcallback() can
also run in tasklet context as the channel event callback.

With CONFIG_PROVE_LOCKING=y in the latest mainline, or
old kernels that don't have commit f71b74bca637 ("irq/softirqs: Use lockdep
to assert IRQs are disabled/enabled"), it turns out can we trigger a warning
at the beginning of __local_bh_enable_ip(), because the upper layer
irq code can call hv_compose_msi_msg() with local irqs disabled.

Let's fix the warning by switching to local_irq_save()/restore(). This
is not an issue because hv_pci_onchannelcallback() is not slow, and it
not a hot path.

Fixes: de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in hv_compose_msi_msg()")
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
---

A trimmed version of the warning is:

  IRQs not enabled as expected
  WARNING: CPU: 0 PID: 408 at kernel/softirq.c:162 __local_bh_enable_ip+0xb0/0xe0
  Call Trace:
   hv_compose_msi_msg+0x209/0x462 [pci_hyperv]
   irq_chip_compose_msi_msg+0x41/0x50
   msi_domain_activate+0x1a/0x40
   __irq_domain_activate_irq+0x59/0x90
   irq_domain_activate_irq+0x25/0x40
   __setup_irq+0x3ec/0x730
  request_threaded_irq+0xfa/0x1a0
  mlx4_init_eq_table+0x3c3/0x5f0 [mlx4_core]
  mlx4_setup_hca+0x1db/0x750 [mlx4_core]
  mlx4_load_one+0xad2/0x13b0 [mlx4_core]
  mlx4_init_one+0x578/0x710 [mlx4_core]
  local_pci_probe+0x1e/0x50
  work_for_cpu_fn+0x10/0x20
  process_one_work+0x1d4/0x5a0
  worker_thread+0x1cb/0x3d0
  kthread+0xf5/0x130

 drivers/pci/host/pci-hyperv.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
index 50cdefe..ad6a64d 100644
--- a/drivers/pci/host/pci-hyperv.c
+++ b/drivers/pci/host/pci-hyperv.c
@@ -1051,6 +1051,7 @@ static u32 hv_compose_msi_req_v2(
  */
 static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
 {
+	unsigned long flags;
 	struct irq_cfg *cfg = irqd_cfg(data);
 	struct hv_pcibus_device *hbus;
 	struct hv_pci_dev *hpdev;
@@ -1148,14 +1149,14 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
 		 * the channel callback directly when channel->target_cpu is
 		 * the current CPU. When the higher level interrupt code
 		 * calls us with interrupt enabled, let's add the
-		 * local_bh_disable()/enable() to avoid race.
+		 * local_irq_save()/restore() to avoid race.
 		 */
-		local_bh_disable();
+		local_irq_save(flags);
 
 		if (hbus->hdev->channel->target_cpu == smp_processor_id())
 			hv_pci_onchannelcallback(hbus);
 
-		local_bh_enable();
+		local_irq_restore(flags);
 
 		if (hpdev->state == hv_pcichild_ejecting) {
 			dev_err_once(&hbus->hdev->device,
-- 
2.7.4