Commit 1d044ca0 authored by Guilherme G. Piccoli's avatar Guilherme G. Piccoli Committed by Wei Liu
Browse files

video: hyperv_fb: Avoid taking busy spinlock on panic path 



The Hyper-V framebuffer code registers a panic notifier in order
to try updating its fbdev if the kernel crashed. The notifier
callback is straightforward, but it calls the vmbus_sendpacket()
routine eventually, and such function takes a spinlock for the
ring buffer operations.

Panic path runs in atomic context, with local interrupts and
preemption disabled, and all secondary CPUs shutdown. That said,
taking a spinlock might cause a lockup if a secondary CPU was
disabled with such lock taken. Fix it here by checking if the
ring buffer spinlock is busy on Hyper-V framebuffer panic notifier;
if so, bail-out avoiding the potential lockup scenario.

Cc: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Michael Kelley <mikelley@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Tested-by: default avatarFabio A M Martins <fabiomirmar@gmail.com>
Signed-off-by: default avatarGuilherme G. Piccoli <gpiccoli@igalia.com>
Reviewed-by: default avatarMichael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20220819221731.480795-10-gpiccoli@igalia.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
parent dc60f2db

drivers/hv/ring_buffer.c

+13 −0
Original line number Diff line number Diff line
@@ -280,6 +280,19 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info) 
	ring_info->pkt_buffer_size = 0;

}



/*

 * Check if the ring buffer spinlock is available to take or not; used on

 * atomic contexts, like panic path (see the Hyper-V framebuffer driver).

 */



bool hv_ringbuffer_spinlock_busy(struct vmbus_channel *channel)

{

	struct hv_ring_buffer_info *rinfo = &channel->outbound;



	return spin_is_locked(&rinfo->ring_lock);

}

EXPORT_SYMBOL_GPL(hv_ringbuffer_spinlock_busy);



/* Write to the ring buffer. */

int hv_ringbuffer_write(struct vmbus_channel *channel,

			const struct kvec *kv_list, u32 kv_count,

drivers/video/fbdev/hyperv_fb.c

+7 −1
Original line number Diff line number Diff line
@@ -780,12 +780,18 @@ static void hvfb_ondemand_refresh_throttle(struct hvfb_par *par, 
static int hvfb_on_panic(struct notifier_block *nb,

			 unsigned long e, void *p)

{

	struct hv_device *hdev;

	struct hvfb_par *par;

	struct fb_info *info;



	par = container_of(nb, struct hvfb_par, hvfb_panic_nb);

	par->synchronous_fb = true;

	info = par->info;

	hdev = device_to_hv_device(info->device);



	if (hv_ringbuffer_spinlock_busy(hdev->channel))

		return NOTIFY_DONE;



	par->synchronous_fb = true;

	if (par->need_docopy)

		hvfb_docopy(par, 0, dio_fb_size);

	synthvid_update(info, 0, 0, INT_MAX, INT_MAX);

include/linux/hyperv.h

+2 −0
Original line number Diff line number Diff line
@@ -1341,6 +1341,8 @@ struct hv_ring_buffer_debug_info { 
int hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,

				struct hv_ring_buffer_debug_info *debug_info);



bool hv_ringbuffer_spinlock_busy(struct vmbus_channel *channel);



/* Vmbus interface */

#define vmbus_driver_register(driver)	\

	__vmbus_driver_register(driver, THIS_MODULE, KBUILD_MODNAME)