From: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> Sent: Friday, August 19, 2022 3:17 PM > > 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@xxxxxxxxx> > Cc: Dexuan Cui <decui@xxxxxxxxxxxxx> > Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> > Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> > Cc: Michael Kelley <mikelley@xxxxxxxxxxxxx> > Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx> > Cc: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> > Cc: Wei Liu <wei.liu@xxxxxxxxxx> > Tested-by: Fabio A M Martins <fabiomirmar@xxxxxxxxx> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> > > --- > > V3: > - simplified the code based on Michael's suggestion - thanks! > > V2: > - new patch, based on the discussion in [0]. > [0] https://lore.kernel.org/lkml/2787b476-6366-1c83-db80-0393da417497@xxxxxxxxxx/ > > > 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 59a4aa86d1f3..c6692fd5ab15 100644 > --- a/drivers/hv/ring_buffer.c > +++ b/drivers/hv/ring_buffer.c > @@ -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, > diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c > index 886c564787f1..e1b65a01fb96 100644 > --- a/drivers/video/fbdev/hyperv_fb.c > +++ b/drivers/video/fbdev/hyperv_fb.c > @@ -783,12 +783,18 @@ 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 3b42264333ef..646f1da9f27e 100644 > --- a/include/linux/hyperv.h > +++ b/include/linux/hyperv.h > @@ -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) > -- > 2.37.2 Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx> _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
