From: Guilherme G. Piccoli gpiccoli@igalia.com
[ Upstream commit 1d044ca035dc22df0d3b39e56f2881071d9118bd ]
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: Fabio A M Martins fabiomirmar@gmail.com Signed-off-by: Guilherme G. Piccoli gpiccoli@igalia.com Reviewed-by: Michael Kelley mikelley@microsoft.com Link: https://lore.kernel.org/r/20220819221731.480795-10-gpiccoli@igalia.com Signed-off-by: Wei Liu wei.liu@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/hv/ring_buffer.c | 13 +++++++++++++ drivers/video/fbdev/hyperv_fb.c | 8 +++++++- include/linux/hyperv.h | 2 ++ 3 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c index 769851b6e74c..7ed6fad3fa8f 100644 --- a/drivers/hv/ring_buffer.c +++ b/drivers/hv/ring_buffer.c @@ -246,6 +246,19 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info) mutex_unlock(&ring_info->ring_buffer_mutex); }
+/* + * 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) diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c index 40baa79f8046..f0a66a344d87 100644 --- a/drivers/video/fbdev/hyperv_fb.c +++ b/drivers/video/fbdev/hyperv_fb.c @@ -798,12 +798,18 @@ 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); diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h index 1ce131f29f3b..eada4d8d6587 100644 --- a/include/linux/hyperv.h +++ b/include/linux/hyperv.h @@ -1269,6 +1269,8 @@ 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)