linux-kernel - RE: [PATCH v3 2/2] fbdev: hyperv_fb: Allow graceful removal of framebuffer

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Message-ID:
 <BN7PR02MB4148986520E4843A34300436D4CA2@BN7PR02MB4148.namprd02.prod.outlook.com>
Date: Thu, 6 Mar 2025 03:06:54 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Saurabh Sengar <ssengar@...ux.microsoft.com>, "kys@...rosoft.com"
	<kys@...rosoft.com>, "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
	"wei.liu@...nel.org" <wei.liu@...nel.org>, "decui@...rosoft.com"
	<decui@...rosoft.com>, "deller@....de" <deller@....de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "ssengar@...rosoft.com" <ssengar@...rosoft.com>
Subject: RE: [PATCH v3 2/2] fbdev: hyperv_fb: Allow graceful removal of
 framebuffer

From: Saurabh Sengar <ssengar@...ux.microsoft.com> Sent: Saturday, March 1, 2025 8:17 AM
> 
> When a Hyper-V framebuffer device is unbind, hyperv_fb driver tries to
> release the framebuffer forcefully. If this framebuffer is in use it
> produce the following WARN and hence this framebuffer is never released.
> 
> [   44.111220] WARNING: CPU: 35 PID: 1882 at drivers/video/fbdev/core/fb_info.c:70
> framebuffer_release+0x2c/0x40
> < snip >
> [   44.111289] Call Trace:
> [   44.111290]  <TASK>
> [   44.111291]  ? show_regs+0x6c/0x80
> [   44.111295]  ? __warn+0x8d/0x150
> [   44.111298]  ? framebuffer_release+0x2c/0x40
> [   44.111300]  ? report_bug+0x182/0x1b0
> [   44.111303]  ? handle_bug+0x6e/0xb0
> [   44.111306]  ? exc_invalid_op+0x18/0x80
> [   44.111308]  ? asm_exc_invalid_op+0x1b/0x20
> [   44.111311]  ? framebuffer_release+0x2c/0x40
> [   44.111313]  ? hvfb_remove+0x86/0xa0 [hyperv_fb]
> [   44.111315]  vmbus_remove+0x24/0x40 [hv_vmbus]
> [   44.111323]  device_remove+0x40/0x80
> [   44.111325]  device_release_driver_internal+0x20b/0x270
> [   44.111327]  ? bus_find_device+0xb3/0xf0
> 
> Fix this by moving the release of framebuffer and assosiated memory
> to fb_ops.fb_destroy function, so that framebuffer framework handles
> it gracefully.
> 
> While we fix this, also replace manual registrations/unregistration of
> framebuffer with devm_register_framebuffer.
> 
> Fixes: 68a2d20b79b1 ("drivers/video: add Hyper-V Synthetic Video Frame Buffer Driver")
> 
> Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> ---
> [V3]
>  - using simplified hvfb_putmem()
> 
>  drivers/video/fbdev/hyperv_fb.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
> index 09fb025477f7..76a42379c8df 100644
> --- a/drivers/video/fbdev/hyperv_fb.c
> +++ b/drivers/video/fbdev/hyperv_fb.c
> @@ -282,6 +282,8 @@ static uint screen_depth;
>  static uint screen_fb_size;
>  static uint dio_fb_size; /* FB size for deferred IO */
> 
> +static void hvfb_putmem(struct fb_info *info);
> +
>  /* Send message to Hyper-V host */
>  static inline int synthvid_send(struct hv_device *hdev,
>  				struct synthvid_msg *msg)
> @@ -862,6 +864,17 @@ static void hvfb_ops_damage_area(struct fb_info *info, u32 x, u32 y, u32 width,
>  		hvfb_ondemand_refresh_throttle(par, x, y, width, height);
>  }
> 
> +/*
> + * fb_ops.fb_destroy is called by the last put_fb_info() call at the end
> + * of unregister_framebuffer() or fb_release(). Do any cleanup related to
> + * framebuffer here.
> + */
> +static void hvfb_destroy(struct fb_info *info)
> +{
> +	hvfb_putmem(info);
> +	framebuffer_release(info);
> +}
> +
>  /*
>   * TODO: GEN1 codepaths allocate from system or DMA-able memory. Fix the
>   *       driver to use the _SYSMEM_ or _DMAMEM_ helpers in these cases.
> @@ -877,6 +890,7 @@ static const struct fb_ops hvfb_ops = {
>  	.fb_set_par = hvfb_set_par,
>  	.fb_setcolreg = hvfb_setcolreg,
>  	.fb_blank = hvfb_blank,
> +	.fb_destroy	= hvfb_destroy,
>  };
> 
>  /* Get options from kernel paramenter "video=" */
> @@ -1172,7 +1186,7 @@ static int hvfb_probe(struct hv_device *hdev,
>  	if (ret)
>  		goto error;
> 
> -	ret = register_framebuffer(info);
> +	ret = devm_register_framebuffer(&hdev->device, info);
>  	if (ret) {
>  		pr_err("Unable to register framebuffer\n");
>  		goto error;
> @@ -1220,14 +1234,10 @@ static void hvfb_remove(struct hv_device *hdev)
> 
>  	fb_deferred_io_cleanup(info);
> 
> -	unregister_framebuffer(info);
>  	cancel_delayed_work_sync(&par->dwork);
> 
>  	vmbus_close(hdev->channel);
>  	hv_set_drvdata(hdev, NULL);
> -
> -	hvfb_putmem(info);
> -	framebuffer_release(info);
>  }
> 
>  static int hvfb_suspend(struct hv_device *hdev)
> --
> 2.43.0

Reviewed-by: Michael Kelley <mhklinux@...look.com>
Tested-by: Michael Kelley <mhklinux@...look.com>