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    SubjectRe: [REGRESSION] commit 66c1ca0: {fbmem: fix fb_info->lock and mm->mmap_sem ...} causes Xfbdev not working
    On Sat, Apr 11, 2009 at 01:08:41PM +0200, Andrea Righi wrote:
    > On Sat, Apr 11, 2009 at 11:00:38AM +0200, Stefan Richter wrote:
    > > Krzysztof Helt wrote:
    > > > On Sat, 11 Apr 2009 00:05:22 +0200
    > > > Andrea Righi <righi.andrea@gmail.com> wrote:
    > > >
    > > >> mmmh... I may have missed something, but the common fb_mmap() should
    > > >> acquire mm->mmap_sem and then info->lock, while fb_ioctl() can do that
    > > >> in reverse order (info->lock first and then mm->mmap_sem) causing the
    > > >> circular locking dependency. Are you sure that pushing info->lock down
    > > >> each driver's fb_mmap will fix the problem?
    > > >
    > > > Right. The fb_mmap is called with the mmap_sem already held.
    > > > I will try other possibilities like breaking info->lock() into two
    > > > mutexex.
    > >
    > > I had to deal with interaction of mmap_sem with a driver lock twice yet.
    > > I solved it cheaply by replacing mutex_lock(driver_mutex) by
    > > mutex_trylock(driver_mutex).
    > >
    > > The obvious drawback is that thic changes kernel behaviour visibly to
    > > userspace: Under contention, the ioctl/read/write fails with -EAGAIN
    > > instead of being blocked until the other thread finished its
    > > ioctl/read/write/mmap on the same fd (if the driver mutex is
    > > instantiated per fd, like in my case).
    > >
    > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=8449fc3ae58bf8ee5acbd2280754cde67b5db128
    > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=638570b54346f140bc09b986d93e76025d35180f
    > >
    > > (In these two drivers, the change of behaviour is irrelevant to real
    > > userspace clients.)
    >
    > I've looked at the code again. I think the main problem here (at last
    > the last one reported) is that fb_notifier_call_chain() is called with
    > info->lock held, i.e. in do_fb_ioctl() => FBIOPUT_VSCREENINFO =>
    > fb_set_var() and the some notifier callbacks, like fbcon_event_notify(),
    > try to re-acquire info->lock again.
    >
    > Probably we can just remove the lock/unlock_fb_info() in all the fb
    > notifier callbacks' and be sure to always call fb_notifier_call_chain()
    > with info->lock held.
    >
    > Something like this (untested). I'll test it later and re-submit if it
    > makes sense.

    Tested intelfb and X11 with fbdev. It seems to work fine, but I may be
    unable to test the mode switching right now:

    intelfb: Non-CRT device is enabled ( LVDS port ). Disabling mode switching.

    It would be great if someone could help me to test this patch (against
    latest Linus' git - no need to revert 66c1ca).

    Thanks,
    -Andrea

    ---
    fbdev: fix info->lock deadlock in fbcon_event_notify()

    fb_notifier_call_chain() is called with info->lock held, i.e. in
    do_fb_ioctl() => FBIOPUT_VSCREENINFO => fb_set_var() and the some
    notifier callbacks, like fbcon_event_notify(), try to re-acquire
    info->lock again.

    Remove the lock/unlock_fb_info() in all the framebuffer notifier
    callbacks' and be sure to always call fb_notifier_call_chain() with
    info->lock held.

    Reported-by: Pavel Roskin <proski@gnu.org>
    Reported-by: Eric Miao <eric.y.miao@gmail.com>
    Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
    ---
    drivers/video/backlight/backlight.c | 3 --
    drivers/video/backlight/lcd.c | 3 --
    drivers/video/console/fbcon.c | 55 ++---------------------------------
    drivers/video/fbmem.c | 19 ++++++++++++
    4 files changed, 22 insertions(+), 58 deletions(-)

    diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
    index dd37cbc..157057c 100644
    --- a/drivers/video/backlight/backlight.c
    +++ b/drivers/video/backlight/backlight.c
    @@ -35,8 +35,6 @@ static int fb_notifier_callback(struct notifier_block *self,
    return 0;

    bd = container_of(self, struct backlight_device, fb_notif);
    - if (!lock_fb_info(evdata->info))
    - return -ENODEV;
    mutex_lock(&bd->ops_lock);
    if (bd->ops)
    if (!bd->ops->check_fb ||
    @@ -49,7 +47,6 @@ static int fb_notifier_callback(struct notifier_block *self,
    backlight_update_status(bd);
    }
    mutex_unlock(&bd->ops_lock);
    - unlock_fb_info(evdata->info);
    return 0;
    }

    diff --git a/drivers/video/backlight/lcd.c b/drivers/video/backlight/lcd.c
    index 0bb13df..b644947 100644
    --- a/drivers/video/backlight/lcd.c
    +++ b/drivers/video/backlight/lcd.c
    @@ -40,8 +40,6 @@ static int fb_notifier_callback(struct notifier_block *self,
    if (!ld->ops)
    return 0;

    - if (!lock_fb_info(evdata->info))
    - return -ENODEV;
    mutex_lock(&ld->ops_lock);
    if (!ld->ops->check_fb || ld->ops->check_fb(ld, evdata->info)) {
    if (event == FB_EVENT_BLANK) {
    @@ -53,7 +51,6 @@ static int fb_notifier_callback(struct notifier_block *self,
    }
    }
    mutex_unlock(&ld->ops_lock);
    - unlock_fb_info(evdata->info);
    return 0;
    }

    diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
    index 2cd500a..471a9a6 100644
    --- a/drivers/video/console/fbcon.c
    +++ b/drivers/video/console/fbcon.c
    @@ -2263,9 +2263,12 @@ static void fbcon_generic_blank(struct vc_data *vc, struct fb_info *info,
    }


    + if (!lock_fb_info(info))
    + return;
    event.info = info;
    event.data = &blank;
    fb_notifier_call_chain(FB_EVENT_CONBLANK, &event);
    + unlock_fb_info(info);
    }

    static int fbcon_blank(struct vc_data *vc, int blank, int mode_switch)
    @@ -2956,8 +2959,6 @@ static int fbcon_fb_unregistered(struct fb_info *info)
    {
    int i, idx;

    - if (!lock_fb_info(info))
    - return -ENODEV;
    idx = info->node;
    for (i = first_fb_vc; i <= last_fb_vc; i++) {
    if (con2fb_map[i] == idx)
    @@ -2985,8 +2986,6 @@ static int fbcon_fb_unregistered(struct fb_info *info)
    if (primary_device == idx)
    primary_device = -1;

    - unlock_fb_info(info);
    -
    if (!num_registered_fb)
    unregister_con_driver(&fb_con);

    @@ -3027,11 +3026,8 @@ static int fbcon_fb_registered(struct fb_info *info)
    {
    int ret = 0, i, idx;

    - if (!lock_fb_info(info))
    - return -ENODEV;
    idx = info->node;
    fbcon_select_primary(info);
    - unlock_fb_info(info);

    if (info_idx == -1) {
    for (i = first_fb_vc; i <= last_fb_vc; i++) {
    @@ -3152,53 +3148,23 @@ static int fbcon_event_notify(struct notifier_block *self,

    switch(action) {
    case FB_EVENT_SUSPEND:
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    fbcon_suspended(info);
    - unlock_fb_info(info);
    break;
    case FB_EVENT_RESUME:
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    fbcon_resumed(info);
    - unlock_fb_info(info);
    break;
    case FB_EVENT_MODE_CHANGE:
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    fbcon_modechanged(info);
    - unlock_fb_info(info);
    break;
    case FB_EVENT_MODE_CHANGE_ALL:
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    fbcon_set_all_vcs(info);
    - unlock_fb_info(info);
    break;
    case FB_EVENT_MODE_DELETE:
    mode = event->data;
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    ret = fbcon_mode_deleted(info, mode);
    - unlock_fb_info(info);
    break;
    case FB_EVENT_FB_UNBIND:
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    idx = info->node;
    - unlock_fb_info(info);
    ret = fbcon_fb_unbind(idx);
    break;
    case FB_EVENT_FB_REGISTERED:
    @@ -3217,29 +3183,14 @@ static int fbcon_event_notify(struct notifier_block *self,
    con2fb->framebuffer = con2fb_map[con2fb->console - 1];
    break;
    case FB_EVENT_BLANK:
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    fbcon_fb_blanked(info, *(int *)event->data);
    - unlock_fb_info(info);
    break;
    case FB_EVENT_NEW_MODELIST:
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    fbcon_new_modelist(info);
    - unlock_fb_info(info);
    break;
    case FB_EVENT_GET_REQ:
    caps = event->data;
    - if (!lock_fb_info(info)) {
    - ret = -ENODEV;
    - goto done;
    - }
    fbcon_get_requirement(info, caps);
    - unlock_fb_info(info);
    break;
    }
    done:
    diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
    index 2ac32e6..d412a1d 100644
    --- a/drivers/video/fbmem.c
    +++ b/drivers/video/fbmem.c
    @@ -1097,8 +1097,11 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
    return -EINVAL;
    con2fb.framebuffer = -1;
    event.data = &con2fb;
    + if (!lock_fb_info(info))
    + return -ENODEV;
    event.info = info;
    fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP, &event);
    + unlock_fb_info(info);
    ret = copy_to_user(argp, &con2fb, sizeof(con2fb)) ? -EFAULT : 0;
    break;
    case FBIOPUT_CON2FBMAP:
    @@ -1115,8 +1118,11 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
    break;
    }
    event.data = &con2fb;
    + if (!lock_fb_info(info))
    + return -ENODEV;
    event.info = info;
    ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
    + unlock_fb_info(info);
    break;
    case FBIOBLANK:
    if (!lock_fb_info(info))
    @@ -1521,7 +1527,10 @@ register_framebuffer(struct fb_info *fb_info)
    registered_fb[i] = fb_info;

    event.info = fb_info;
    + if (!lock_fb_info(fb_info))
    + return -ENODEV;
    fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
    + unlock_fb_info(fb_info);
    return 0;
    }

    @@ -1555,8 +1564,12 @@ unregister_framebuffer(struct fb_info *fb_info)
    goto done;
    }

    +
    + if (!lock_fb_info(fb_info))
    + return -ENODEV;
    event.info = fb_info;
    ret = fb_notifier_call_chain(FB_EVENT_FB_UNBIND, &event);
    + unlock_fb_info(fb_info);

    if (ret) {
    ret = -EINVAL;
    @@ -1590,6 +1603,8 @@ void fb_set_suspend(struct fb_info *info, int state)
    {
    struct fb_event event;

    + if (!lock_fb_info(info))
    + return;
    event.info = info;
    if (state) {
    fb_notifier_call_chain(FB_EVENT_SUSPEND, &event);
    @@ -1598,6 +1613,7 @@ void fb_set_suspend(struct fb_info *info, int state)
    info->state = FBINFO_STATE_RUNNING;
    fb_notifier_call_chain(FB_EVENT_RESUME, &event);
    }
    + unlock_fb_info(info);
    }

    /**
    @@ -1667,8 +1683,11 @@ int fb_new_modelist(struct fb_info *info)
    err = 1;

    if (!list_empty(&info->modelist)) {
    + if (!lock_fb_info(info))
    + return -ENODEV;
    event.info = info;
    err = fb_notifier_call_chain(FB_EVENT_NEW_MODELIST, &event);
    + unlock_fb_info(info);
    }

    return err;

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      Last update: 2009-04-11 17:07    [W:0.042 / U:3.164 seconds]
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