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Message-Id: <20221217001058.41426-3-sashal@kernel.org>
Date: Fri, 16 Dec 2022 19:10:55 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
Andrea Parri <parri.andrea@...il.com>,
Dexuan Cui <decui@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
"K. Y. Srinivasan" <kys@...rosoft.com>,
Michael Kelley <mikelley@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
Tianyu Lan <Tianyu.Lan@...rosoft.com>,
Wei Liu <wei.liu@...nel.org>,
Fabio A M Martins <fabiomirmar@...il.com>,
Sasha Levin <sashal@...nel.org>, deller@....de,
linux-hyperv@...r.kernel.org, linux-fbdev@...r.kernel.org,
dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 5.10 3/5] video: hyperv_fb: Avoid taking busy spinlock on panic path
From: "Guilherme G. Piccoli" <gpiccoli@...lia.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@...il.com>
Cc: Dexuan Cui <decui@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
Cc: Michael Kelley <mikelley@...rosoft.com>
Cc: Stephen Hemminger <sthemmin@...rosoft.com>
Cc: Tianyu Lan <Tianyu.Lan@...rosoft.com>
Cc: Wei Liu <wei.liu@...nel.org>
Tested-by: Fabio A M Martins <fabiomirmar@...il.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
Link: https://lore.kernel.org/r/20220819221731.480795-10-gpiccoli@igalia.com
Signed-off-by: Wei Liu <wei.liu@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.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)
--
2.35.1
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