Re: [PATCH v2] PCI: hv: Disable/enable irq rather than bh in hv_compose_msi_msg()

[Lorenzo Pieralisi]

On Sun, Jul 01, 2018 at 06:22:23PM +0000, Dexuan Cui wrote:
> 
> 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, and here we
> want to avoid the race.
> 
> With CONFIG_PROVE_LOCKING=y in the recent mainline, or old kernels that
> don't have commit f71b74bca637 ("irq/softirqs: Use lockdep to assert IRQs
> are disabled/enabled"), when the upper layer irq code calls
> hv_compose_msi_msg() with local irq DISABLED, we'll see a warning at the
> beginning of __local_bh_enable_ip():
> 
> IRQs not enabled as expected
>   WARNING: CPU: 0 PID: 408 at kernel/softirq.c:162 __local_bh_enable_ip
> 
> The warning exposes an issue in de0aa7b2f97d: local_bh_enable() can
> potentially call do_softirq(), which is not supposed to run when local
> irq is DISABLED. Let's fix this by using local_irq_save()/restore()
> instead.
> 
> Note: hv_pci_onchannelcallback() is not a hot path because it's only
> called when the PCI device is hot added and removed, which is infrequent.
> 
> Fixes: de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in hv_compose_msi_msg()")
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Reviewed-by: Haiyang Zhang <haiyangz@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
> 
> 
> Changes since v1:
> 	Updated the changelog only (fixed typos and some inaccuracy)
> 
> 
>  drivers/pci/controller/pci-hyperv.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)

Applied to pci/controller-fixes, to be tentatively sent for an
upcoming -rc, thanks.

Lorenzo

> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index ba1d4b5..eb20296 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -1073,6 +1073,7 @@ static void hv_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
>  	struct pci_bus *pbus;
>  	struct pci_dev *pdev;
>  	struct cpumask *dest;
> +	unsigned long flags;
>  	struct compose_comp_ctxt comp;
>  	struct tran_int_desc *int_desc;
>  	struct {
> @@ -1164,14 +1165,15 @@ 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:
> +		 * hv_pci_onchannelcallback() can also run in tasklet.
>  		 */
> -		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
>