From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 66D1779C9 for ; Thu, 12 Jan 2023 14:24:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AF3BFC433EF; Thu, 12 Jan 2023 14:24:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1673533457; bh=hp465M9wGjdwI3k7l0E7ijLFOCdkphTJgF78bjhCsLE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AEYrF/MFog/nflNz5hYsiCX+t3xbWt8uIyfOl/3FxuNppxwargFv5fz8MI/LXnDhn 0X96lKu/f2kuRRDsieVeOfZ2lh1i14sru5p0TMEDEURcLsjRTYrGTp+zME1YHrlC+8 aKenUCtqV3UlYH9dCy32Of+LSfyN4KjDN6VNXjYM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Andrea Parri (Microsoft)" , Dexuan Cui , Haiyang Zhang , "K. Y. Srinivasan" , Michael Kelley , Stephen Hemminger , Tianyu Lan , Wei Liu , Fabio A M Martins , "Guilherme G. Piccoli" , Sasha Levin Subject: [PATCH 5.10 485/783] video: hyperv_fb: Avoid taking busy spinlock on panic path Date: Thu, 12 Jan 2023 14:53:21 +0100 Message-Id: <20230112135546.668491735@linuxfoundation.org> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20230112135524.143670746@linuxfoundation.org> References: <20230112135524.143670746@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Guilherme G. Piccoli [ 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) Cc: Dexuan Cui Cc: Haiyang Zhang Cc: "K. Y. Srinivasan" Cc: Michael Kelley Cc: Stephen Hemminger Cc: Tianyu Lan Cc: Wei Liu Tested-by: Fabio A M Martins Signed-off-by: Guilherme G. Piccoli Reviewed-by: Michael Kelley Link: https://lore.kernel.org/r/20220819221731.480795-10-gpiccoli@igalia.com Signed-off-by: Wei Liu Signed-off-by: Sasha Levin --- 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