Re: vfree() and mmap()ed framebuffer with defio (Was: Deadlock between fbcon and fb_defio?)

Bruno Prémont
2010-05-26T19:58:57Z

Hi Jaya,

On Mon, 10 May 2010 Bruno Prémont <bonbons@linux-vserver.org> wrote:
> I want to make sure that I won't be accessing the old framebuffer after
> freeing it and also that defio monitors the new framebuffer.
>
> For that reason I defio_cleanup(), replace framebuffer, defio_init().
> All of this happens while do_fb_ioctl() holds lock on fb_info and
> console_sem.

I've slightly changed the code path when releasing old valloc()ed
framebuffer. Now I don't call defio_init/cleanup while framebuffer is
registered so the deadlock cannot happen. But just calling vfree()
to dispose old framebuffer is not sufficient when it was mmap()ed.

Do you know how I could "get rid" of that old framebuffer in a proper
way?

Currently I'm getting the complaints from kernel when the process that
mmap()ed frambuffer exits after depth changed via set_par() or even a
"BUG: unable to handle kernel paging request" (depending on what exactly
I do (pertinent hunk of patch, full patch at the end):

@@ -574,7 +611,10 @@ static int picolcd_set_par(struct fb_info *info)
info->screen_base = (char __force __iomem *)n_fb;
info->fix.smem_start = (unsigned long)n_fb;
info->fix.smem_len = PICOLCDFB_SIZE*data->fb_bpp;
- fb_deferred_io_init(info);
+ for (i = 0; i < o_len; i += PAGE_SIZE) {
+ struct page *page = vmalloc_to_page(o_fb + i);
+ page->mapping = NULL;
+ }
vfree(o_fb);
return 0;
}

If I run the for loop I end up with the "unable to handle paging request" BUG:
[ 4364.740056] BUG: unable to handle kernel paging request at 84db1980
[ 4364.741115] IP: [<c103816f>] __wake_up_bit+0xf/0x30
[ 4364.741806] *pde = 00000000
[ 4364.742165] Oops: 0000 [#1]
[ 4364.742526] last sysfs file: /sys/devices/platform/via_cputemp.0/temp1_input
[ 4364.743559] Modules linked in: hid_picolcd e_powersaver via_cputemp snd_hda_codec_via snd_hda_intel snd_hda_codec backlight snd_pcm lcd led_class snd_timer fb_sys_fops sysimgblt sysfillrect syscopyarea snd soundcore snd_page_alloc sg [last unloaded: hid_picolcd]
[ 4364.747026]
[ 4364.747393] Pid: 5, comm: events/0 Tainted: G B 2.6.34-venus #46 CX700+W697HG/CX700+W697HG
[ 4364.748855] EIP: 0060:[<c103816f>] EFLAGS: 00010296 CPU: 0
[ 4364.749603] EIP is at __wake_up_bit+0xf/0x30
[ 4364.750012] EAX: 84db1980 EBX: 84db1980 ECX: 00000000 EDX: c14b6330
[ 4364.750012] ESI: f69b4874 EDI: f69b4864 EBP: f704af54 ESP: f704af44
[ 4364.750012] DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068
[ 4364.750012] Process events/0 (pid: 5, ti=f704a000 task=f704edc0 task.ti=f704a000)
[ 4364.750012] Stack:
[ 4364.750012] 00000000 c14b6330 00000000 c14b65cc f704af60 c105b39d c14b6330 f704af7c
[ 4364.750012] <0> c11a2e96 f69b4868 f69b2800 f69b2a1c f7003300 c11a2e50 f704afc0 c1035056
[ 4364.750012] <0> c10228ef f704e000 f704edc0 f704e000 f704efa0 f704edc0 f7003308 00000000
[ 4364.750012] Call Trace:
[ 4364.750012] [<c105b39d>] ? unlock_page+0x3d/0x40
[ 4364.750012] [<c11a2e96>] ? fb_deferred_io_work+0x46/0xc0
[ 4364.750012] [<c11a2e50>] ? fb_deferred_io_work+0x0/0xc0
[ 4364.750012] [<c1035056>] ? worker_thread+0xd6/0x180
[ 4364.750012] [<c10228ef>] ? finish_task_switch+0x2f/0x80
[ 4364.750012] [<c1038210>] ? autoremove_wake_function+0x0/0x50
[ 4364.750012] [<c1034f80>] ? worker_thread+0x0/0x180
[ 4364.750012] [<c1037e4c>] ? kthread+0x6c/0x80
[ 4364.750012] [<c1037de0>] ? kthread+0x0/0x80
[ 4364.750012] [<c1003036>] ? kernel_thread_helper+0x6/0x10
[ 4364.750012] Code: 20 5d 4b c1 2b 8b cc 02 00 00 d3 e8 c1 e0 03 03 83 c4 02 00 00 5b 5d c3 8d 74 26 00 55 89 e5 53 89 c3 83 ec 0c 89 55 f4 89 4d f8 <3b> 00 74 17 8d 45 f4 b9 01 00 00 00 89 04 24 ba 03 00 00 00 89
[ 4364.750012] EIP: [<c103816f>] __wake_up_bit+0xf/0x30 SS:ESP 0068:f704af44
[ 4364.750012] CR2: 0000000084db1980
[ 4364.772281] ---[ end trace a9d32c215502d31b ]---

If I don't do the for loop I get on of these for each page of the old
framebuffer still mmap()ed by userspace:
[ 1301.041395] BUG: Bad page state in process links pfn:3b8fa
[ 1301.041867] page:c1d02f40 count:0 mapcount:0 mapping:f6a23be8 index:0x0
[ 1301.042641] page flags: 0x80000014(referenced|dirty)
[ 1301.043420] Pid: 1688, comm: links Not tainted 2.6.34-venus #46
[ 1301.044552] Call Trace:
[ 1301.044972] [<c105eea2>] bad_page+0x82/0xd0
[ 1301.045727] [<c1060341>] free_hot_cold_page+0x191/0x310
[ 1301.046497] [<c1062c1e>] put_page+0x3e/0x100
[ 1301.047256] [<c1078d9d>] free_page_and_swap_cache+0x1d/0x40
[ 1301.048056] [<c106ddc8>] unmap_vmas+0x2a8/0x580
[ 1301.048846] [<c1021ce7>] ? dequeue_task_fair+0x27/0x1d0
[ 1301.049640] [<c1071837>] exit_mmap+0x97/0x110
[ 1301.050477] [<c1023e56>] mmput+0x26/0x90
[ 1301.051259] [<c10274f1>] exit_mm+0xb1/0xc0
[ 1301.052045] [<c10288ba>] do_exit+0xba/0x6b0
[ 1301.052848] [<c102f721>] ? recalc_sigpending+0x11/0x30
[ 1301.053660] [<c1030b9c>] ? dequeue_signal+0x2c/0x130
[ 1301.054480] [<c1028edd>] do_group_exit+0x2d/0x70
[ 1301.055293] [<c10321bc>] get_signal_to_deliver+0x17c/0x370
[ 1301.056103] [<c10299f6>] ? current_fs_time+0x16/0x20
[ 1301.056892] [<c10022f8>] do_notify_resume+0x98/0x820
[ 1301.057690] [<c11d4b6e>] ? tty_unthrottle+0x3e/0x50
[ 1301.058490] [<c10299f6>] ? current_fs_time+0x16/0x20
[ 1301.059303] [<c11d2db0>] ? n_tty_read+0x0/0x680
[ 1301.060134] [<c109153d>] ? sys_select+0x3d/0xb0
[ 1301.060935] [<c1029c2b>] ? sys_gettimeofday+0x2b/0x70
[ 1301.061756] [<c13394d2>] work_notifysig+0x13/0x19

What do I have to do to prevent both errors?
I would guess unmapping the old framebuffer from userspace (or maybe
fail set_par() with -EBUSY? - if so how do I determine if the
framebuffer was mmap()ed?)

Any suggestion is welcome!
Thanks,
Bruno

---

Below patch fixes multiple issues running fbcon on top of hid-picolcd's
framebuffer but still has issues on depth change (c.f. above).
Fixed issues:
- NULL pointer deref in 8-bpp mode when fbcon wants to parse
access color map
- bit-order for 1-bpp is the opposite from the one I expected
- too quick update of framebuffer after registration can cause
parts to the framebuffer to not be pushed to device

diff --git a/drivers/hid/hid-picolcd.c b/drivers/hid/hid-picolcd.c
index 95253b3..599bf4b 100644
--- a/drivers/hid/hid-picolcd.c
+++ b/drivers/hid/hid-picolcd.c
@@ -26,6 +26,7 @@

#include <linux/fb.h>
#include <linux/vmalloc.h>
+#include <linux/mm.h>
#include <linux/backlight.h>
#include <linux/lcd.h>

@@ -127,6 +128,26 @@ static const struct fb_var_screeninfo picolcdfb_var = {
.height = 26,
.bits_per_pixel = 1,
.grayscale = 1,
+ .red = {
+ .offset = 0,
+ .length = 1,
+ .msb_right = 0,
+ },
+ .green = {
+ .offset = 0,
+ .length = 1,
+ .msb_right = 0,
+ },
+ .blue = {
+ .offset = 0,
+ .length = 1,
+ .msb_right = 0,
+ },
+ .transp = {
+ .offset = 0,
+ .length = 0,
+ .msb_right = 0,
+ },
};
#endif /* CONFIG_HID_PICOLCD_FB */

@@ -188,6 +209,7 @@ struct picolcd_data {
/* Framebuffer stuff */
u8 fb_update_rate;
u8 fb_bpp;
+ u8 fb_force;
u8 *fb_vbitmap; /* local copy of what was sent to PicoLCD */
u8 *fb_bitmap; /* framebuffer */
struct fb_info *fb_info;
@@ -346,7 +368,7 @@ static int picolcd_fb_update_tile(u8 *vbitmap, const u8 *bitmap, int bpp,
const u8 *bdata = bitmap + tile * 256 + chip * 8 + b * 32;
for (i = 0; i < 64; i++) {
tdata[i] <<= 1;
- tdata[i] |= (bdata[i/8] >> (7 - i % 8)) & 0x01;
+ tdata[i] |= (bdata[i/8] >> (i % 8)) & 0x01;
}
}
} else if (bpp == 8) {
@@ -399,13 +421,10 @@ static int picolcd_fb_reset(struct picolcd_data *data, int clear)

if (data->fb_bitmap) {
if (clear) {
- memset(data->fb_vbitmap, 0xff, PICOLCDFB_SIZE);
+ memset(data->fb_vbitmap, 0, PICOLCDFB_SIZE);
memset(data->fb_bitmap, 0, PICOLCDFB_SIZE*data->fb_bpp);
- } else {
- /* invert 1 byte in each tile to force resend */
- for (i = 0; i < PICOLCDFB_SIZE; i += 64)
- data->fb_vbitmap[i] = ~data->fb_vbitmap[i];
}
+ data->fb_force = 1;
}

/* schedule first output of framebuffer */
@@ -421,6 +440,9 @@ static void picolcd_fb_update(struct picolcd_data *data)
int chip, tile, n;
unsigned long flags;

+ if (!data)
+ return;
+
spin_lock_irqsave(&data->lock, flags);
if (!(data->status & PICOLCD_READY_FB)) {
spin_unlock_irqrestore(&data->lock, flags);
@@ -440,14 +462,18 @@ static void picolcd_fb_update(struct picolcd_data *data)
for (chip = 0; chip < 4; chip++)
for (tile = 0; tile < 8; tile++)
if (picolcd_fb_update_tile(data->fb_vbitmap,
- data->fb_bitmap, data->fb_bpp, chip, tile)) {
+ data->fb_bitmap, data->fb_bpp, chip, tile) ||
+ data->fb_force) {
n += 2;
+ if (!data->fb_info->par)
+ return; /* device lost! */
if (n >= HID_OUTPUT_FIFO_SIZE / 2) {
usbhid_wait_io(data->hdev);
n = 0;
}
picolcd_fb_send_tile(data->hdev, chip, tile);
}
+ data->fb_force = false;
if (n)
usbhid_wait_io(data->hdev);
}
@@ -526,10 +552,17 @@ static int picolcd_fb_check_var(struct fb_var_screeninfo *var, struct fb_info *i
/* only allow 1/8 bit depth (8-bit is grayscale) */
*var = picolcdfb_var;
var->activate = activate;
- if (bpp >= 8)
+ if (bpp >= 8) {
var->bits_per_pixel = 8;
- else
+ var->red.length = 8;
+ var->green.length = 8;
+ var->blue.length = 8;
+ } else {
var->bits_per_pixel = 1;
+ var->red.length = 1;
+ var->green.length = 1;
+ var->blue.length = 1;
+ }
return 0;
}

@@ -537,18 +570,22 @@ static int picolcd_set_par(struct fb_info *info)
{
struct picolcd_data *data = info->par;
u8 *o_fb, *n_fb;
+ int i;
+ unsigned long o_len;
+ if (!data)
+ return -ENODEV;
if (info->var.bits_per_pixel == data->fb_bpp)
return 0;
/* switch between 1/8 bit depths */
if (info->var.bits_per_pixel != 1 && info->var.bits_per_pixel != 8)
return -EINVAL;

- o_fb = data->fb_bitmap;
- n_fb = vmalloc(PICOLCDFB_SIZE*info->var.bits_per_pixel);
+ o_len = info->fix.smem_len;
+ o_fb = data->fb_bitmap;
+ n_fb = vmalloc(PICOLCDFB_SIZE*info->var.bits_per_pixel);
if (!n_fb)
return -ENOMEM;

- fb_deferred_io_cleanup(info);
/* translate FB content to new bits-per-pixel */
if (info->var.bits_per_pixel == 1) {
int i, b;
@@ -565,7 +602,7 @@ static int picolcd_set_par(struct fb_info *info)
int i;
for (i = 0; i < PICOLCDFB_SIZE * 8; i++)
n_fb[i] = o_fb[i/8] & (0x01 << (7 - i % 8)) ? 0xff : 0x00;
- info->fix.visual = FB_VISUAL_TRUECOLOR;
+ info->fix.visual = FB_VISUAL_DIRECTCOLOR;
info->fix.line_length = PICOLCDFB_WIDTH;
}

@@ -574,7 +611,10 @@ static int picolcd_set_par(struct fb_info *info)
info->screen_base = (char __force __iomem *)n_fb;
info->fix.smem_start = (unsigned long)n_fb;
info->fix.smem_len = PICOLCDFB_SIZE*data->fb_bpp;
- fb_deferred_io_init(info);
+ for (i = 0; i < o_len; i += PAGE_SIZE) {
+ struct page *page = vmalloc_to_page(o_fb + i);
+ page->mapping = NULL;
+ }
vfree(o_fb);
return 0;
}
@@ -660,9 +700,10 @@ static int picolcd_init_framebuffer(struct picolcd_data *data)
{
struct device *dev = &data->hdev->dev;
struct fb_info *info = NULL;
- int error = -ENOMEM;
+ int i, error = -ENOMEM;
u8 *fb_vbitmap = NULL;
u8 *fb_bitmap = NULL;
+ u32 *palette;

fb_bitmap = vmalloc(PICOLCDFB_SIZE*picolcdfb_var.bits_per_pixel);
if (fb_bitmap == NULL) {
@@ -678,12 +719,16 @@ static int picolcd_init_framebuffer(struct picolcd_data *data)

data->fb_update_rate = PICOLCDFB_UPDATE_RATE_DEFAULT;
data->fb_defio = picolcd_fb_defio;
- info = framebuffer_alloc(0, dev);
+ info = framebuffer_alloc(256 * sizeof(u32), dev);
if (info == NULL) {
dev_err(dev, "failed to allocate a framebuffer\n");
goto err_nomem;
}

+ palette = info->par;
+ for (i = 0; i < 256; i++)
+ palette[i] = i > 0 && i < 16 ? 0xff : 0;
+ info->pseudo_palette = info->par;
info->fbdefio = &data->fb_defio;
info->screen_base = (char __force __iomem *)fb_bitmap;
info->fbops = &picolcdfb_ops;
@@ -707,18 +752,20 @@ static int picolcd_init_framebuffer(struct picolcd_data *data)
dev_err(dev, "failed to create sysfs attributes\n");
goto err_cleanup;
}
+ fb_deferred_io_init(info);
data->fb_info = info;
error = register_framebuffer(info);
if (error) {
dev_err(dev, "failed to register framebuffer\n");
goto err_sysfs;
}
- fb_deferred_io_init(info);
/* schedule first output of framebuffer */
+ data->fb_force = 1;
schedule_delayed_work(&info->deferred_work, 0);
return 0;

err_sysfs:
+ fb_deferred_io_cleanup(info);
device_remove_file(dev, &dev_attr_fb_update_rate);
err_cleanup:
data->fb_vbitmap = NULL;
@@ -742,13 +789,13 @@ static void picolcd_exit_framebuffer(struct picolcd_data *data)
if (!info)
return;

+ info->par = NULL;
+ device_remove_file(&data->hdev->dev, &dev_attr_fb_update_rate);
+ unregister_framebuffer(info);
data->fb_vbitmap = NULL;
data->fb_bitmap = NULL;
data->fb_bpp = 0;
data->fb_info = NULL;
- device_remove_file(&data->hdev->dev, &dev_attr_fb_update_rate);
- fb_deferred_io_cleanup(info);
- unregister_framebuffer(info);
vfree(fb_bitmap);
kfree(fb_vbitmap);
}
@@ -2566,6 +2613,11 @@ static void picolcd_remove(struct hid_device *hdev)
spin_lock_irqsave(&data->lock, flags);
data->status |= PICOLCD_FAILED;
spin_unlock_irqrestore(&data->lock, flags);
+ /* short-circuit FB as early as possible in order to
+ * avoid long delays if we host console.
+ */
+ if (data->fb_info)
+ data->fb_info->par = NULL;

picolcd_exit_devfs(data);
device_remove_file(&hdev->dev, &dev_attr_operation_mode);