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SubjectRe: [RFC PATCH RESEND] fb: reorder the lock sequence to fix a potential lockdep
Hi Tomi, Jean,
How about this patch?

Thanks,
Gu


On 10/28/2013 02:01 PM, Gu Zheng wrote:

> Following commits:
> 50e244cc79 fb: rework locking to fix lock ordering on takeover
> e93a9a8687 fb: Yet another band-aid for fixing lockdep mess
> 054430e773 fbcon: fix locking harder
>
> reworked locking to fix related lock ordering on takeover, and introduced console_lock
> into fbmem, but it seems that the new lock sequence(fb_info->lock ---> console_lock)
> is against with the one in console_callback(console_lock ---> fb_info->lock), and leads to
> a potential deadlock as following:
> [ 601.079000] ======================================================
> [ 601.079000] [ INFO: possible circular locking dependency detected ]
> [ 601.079000] 3.11.0 #189 Not tainted
> [ 601.079000] -------------------------------------------------------
> [ 601.079000] kworker/0:3/619 is trying to acquire lock:
> [ 601.079000] (&fb_info->lock){+.+.+.}, at: [<ffffffff81397566>] lock_fb_info+0x26/0x60
> [ 601.079000]
> but task is already holding lock:
> [ 601.079000] (console_lock){+.+.+.}, at: [<ffffffff8141aae3>] console_callback+0x13/0x160
> [ 601.079000]
> which lock already depends on the new lock.
>
> [ 601.079000]
> the existing dependency chain (in reverse order) is:
> [ 601.079000]
> -> #1 (console_lock){+.+.+.}:
> [ 601.079000] [<ffffffff810dc971>] lock_acquire+0xa1/0x140
> [ 601.079000] [<ffffffff810c6267>] console_lock+0x77/0x80
> [ 601.079000] [<ffffffff81399448>] register_framebuffer+0x1d8/0x320
> [ 601.079000] [<ffffffff81cfb4c8>] efifb_probe+0x408/0x48f
> [ 601.079000] [<ffffffff8144a963>] platform_drv_probe+0x43/0x80
> [ 601.079000] [<ffffffff8144853b>] driver_probe_device+0x8b/0x390
> [ 601.079000] [<ffffffff814488eb>] __driver_attach+0xab/0xb0
> [ 601.079000] [<ffffffff814463bd>] bus_for_each_dev+0x5d/0xa0
> [ 601.079000] [<ffffffff81447e6e>] driver_attach+0x1e/0x20
> [ 601.079000] [<ffffffff81447a07>] bus_add_driver+0x117/0x290
> [ 601.079000] [<ffffffff81448fea>] driver_register+0x7a/0x170
> [ 601.079000] [<ffffffff8144a10a>] __platform_driver_register+0x4a/0x50
> [ 601.079000] [<ffffffff8144a12d>] platform_driver_probe+0x1d/0xb0
> [ 601.079000] [<ffffffff81cfb0a1>] efifb_init+0x273/0x292
> [ 601.079000] [<ffffffff81002132>] do_one_initcall+0x102/0x1c0
> [ 601.079000] [<ffffffff81cb80a6>] kernel_init_freeable+0x15d/0x1ef
> [ 601.079000] [<ffffffff8166d2de>] kernel_init+0xe/0xf0
> [ 601.079000] [<ffffffff816914ec>] ret_from_fork+0x7c/0xb0
> [ 601.079000]
> -> #0 (&fb_info->lock){+.+.+.}:
> [ 601.079000] [<ffffffff810dc1d8>] __lock_acquire+0x1e18/0x1f10
> [ 601.079000] [<ffffffff810dc971>] lock_acquire+0xa1/0x140
> [ 601.079000] [<ffffffff816835ca>] mutex_lock_nested+0x7a/0x3b0
> [ 601.079000] [<ffffffff81397566>] lock_fb_info+0x26/0x60
> [ 601.079000] [<ffffffff813a4aeb>] fbcon_blank+0x29b/0x2e0
> [ 601.079000] [<ffffffff81418658>] do_blank_screen+0x1d8/0x280
> [ 601.079000] [<ffffffff8141ab34>] console_callback+0x64/0x160
> [ 601.079000] [<ffffffff8108d855>] process_one_work+0x1f5/0x540
> [ 601.079000] [<ffffffff8108e04c>] worker_thread+0x11c/0x370
> [ 601.079000] [<ffffffff81095fbd>] kthread+0xed/0x100
> [ 601.079000] [<ffffffff816914ec>] ret_from_fork+0x7c/0xb0
> [ 601.079000]
> other info that might help us debug this:
>
> [ 601.079000] Possible unsafe locking scenario:
>
> [ 601.079000] CPU0 CPU1
> [ 601.079000] ---- ----
> [ 601.079000] lock(console_lock);
> [ 601.079000] lock(&fb_info->lock);
> [ 601.079000] lock(console_lock);
> [ 601.079000] lock(&fb_info->lock);
> [ 601.079000]
> *** DEADLOCK ***
>
> so we reorder the lock sequence the same as it in console_callback() to
> avoid this issue.
> Not very sure this change is suitable, any comments is welcome.
>
> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
> ---
> drivers/video/fbmem.c | 50 +++++++++++++++++++++++++++++++-----------------
> 1 files changed, 32 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index dacaf74..010d191 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1108,14 +1108,16 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> case FBIOPUT_VSCREENINFO:
> if (copy_from_user(&var, argp, sizeof(var)))
> return -EFAULT;
> - if (!lock_fb_info(info))
> - return -ENODEV;
> console_lock();
> + if (!lock_fb_info(info)) {
> + console_unlock();
> + return -ENODEV;
> + }
> info->flags |= FBINFO_MISC_USEREVENT;
> ret = fb_set_var(info, &var);
> info->flags &= ~FBINFO_MISC_USEREVENT;
> - console_unlock();
> unlock_fb_info(info);
> + console_unlock();
> if (!ret && copy_to_user(argp, &var, sizeof(var)))
> ret = -EFAULT;
> break;
> @@ -1144,12 +1146,14 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> case FBIOPAN_DISPLAY:
> if (copy_from_user(&var, argp, sizeof(var)))
> return -EFAULT;
> - if (!lock_fb_info(info))
> - return -ENODEV;
> console_lock();
> + if (!lock_fb_info(info)) {
> + console_unlock();
> + return -ENODEV;
> + }
> ret = fb_pan_display(info, &var);
> - console_unlock();
> unlock_fb_info(info);
> + console_unlock();
> if (ret == 0 && copy_to_user(argp, &var, sizeof(var)))
> return -EFAULT;
> break;
> @@ -1184,23 +1188,27 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> break;
> }
> event.data = &con2fb;
> - if (!lock_fb_info(info))
> - return -ENODEV;
> console_lock();
> + if (!lock_fb_info(info)) {
> + console_unlock();
> + return -ENODEV;
> + }
> event.info = info;
> ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
> - console_unlock();
> unlock_fb_info(info);
> + console_unlock();
> break;
> case FBIOBLANK:
> - if (!lock_fb_info(info))
> - return -ENODEV;
> console_lock();
> + if (!lock_fb_info(info)) {
> + console_unlock();
> + return -ENODEV;
> + }
> info->flags |= FBINFO_MISC_USEREVENT;
> ret = fb_blank(info, arg);
> info->flags &= ~FBINFO_MISC_USEREVENT;
> - console_unlock();
> unlock_fb_info(info);
> + console_unlock();
> break;
> default:
> if (!lock_fb_info(info))
> @@ -1660,12 +1668,15 @@ static int do_register_framebuffer(struct fb_info *fb_info)
> registered_fb[i] = fb_info;
>
> event.info = fb_info;
> - if (!lock_fb_info(fb_info))
> - return -ENODEV;
> console_lock();
> + if (!lock_fb_info(fb_info)) {
> + console_unlock();
> + return -ENODEV;
> + }
> +
> fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
> - console_unlock();
> unlock_fb_info(fb_info);
> + console_unlock();
> return 0;
> }
>
> @@ -1678,13 +1689,16 @@ static int do_unregister_framebuffer(struct fb_info *fb_info)
> if (i < 0 || i >= FB_MAX || registered_fb[i] != fb_info)
> return -EINVAL;
>
> - if (!lock_fb_info(fb_info))
> - return -ENODEV;
> console_lock();
> + if (!lock_fb_info(fb_info)) {
> + console_unlock();
> + return -ENODEV;
> + }
> +
> event.info = fb_info;
> ret = fb_notifier_call_chain(FB_EVENT_FB_UNBIND, &event);
> - console_unlock();
> unlock_fb_info(fb_info);
> + console_unlock();
>
> if (ret)
> return -EINVAL;




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