On 19/08/2022 19:17, Guilherme G. Piccoli wrote: > 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(-) > [...] Hi Michael, apologies for the ping. Any reviews/comments on this one are greatly appreciated! Cheers, Guilherme
