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