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) <[email protected]> Cc: Dexuan Cui <[email protected]> Cc: Haiyang Zhang <[email protected]> Cc: "K. Y. Srinivasan" <[email protected]> Cc: Michael Kelley <[email protected]> Cc: Stephen Hemminger <[email protected]> Cc: Tianyu Lan <[email protected]> Cc: Wei Liu <[email protected]> Tested-by: Fabio A M Martins <[email protected]> Signed-off-by: Guilherme G. Piccoli <[email protected]> --- V2: - new patch, based on the discussion in [0]. [0] https://lore.kernel.org/lkml/[email protected]/ drivers/hv/ring_buffer.c | 16 ++++++++++++++++ drivers/video/fbdev/hyperv_fb.c | 8 +++++++- include/linux/hyperv.h | 2 ++ 3 files changed, 25 insertions(+), 1 deletion(-) diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c index 59a4aa86d1f3..9ceb3a7e8d19 100644 --- a/drivers/hv/ring_buffer.c +++ b/drivers/hv/ring_buffer.c @@ -280,6 +280,22 @@ 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; + + if (spin_is_locked(&rinfo->ring_lock)) + return true; + + return false; +} +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) -- 2.37.1 _______________________________________________ kexec mailing list [email protected] http://lists.infradead.org/mailman/listinfo/kexec
