BUG: scheduling while atomic in f_fs when gadget remove driver

[Chen Yu <chenyu56@huawei.com>]

Hi All,

I'm working on Hikey board based around the HiSilicon Kirin 620, with linaro kernel version 4.8.rc1 and I
get below BUG error while extracting USB cable from PC.

The funtion using f_fs is adb and usb_gadget_unregister_driver will be called after extracting USB cable from PC.

[   89.456512s][pid:1,cpu1,init]BUG: scheduling while atomic: init/1/0x00000002
[   89.456573s]Modules linked in:
[   89.456604s]Preemption disabled at:[<ffffffc0006a6dc0>] composite_disconnect+0x30/0xac
[   89.456665s][pid:1,cpu1,init]TGID: 1 Comm: init
[   89.456695s][pid:1,cpu1,init]Call trace:
[   89.456726s][pid:1,cpu1,init][<ffffffc00008a5e0>] dump_backtrace+0x0/0x15c
[   89.456756s][pid:1,cpu1,init][<ffffffc00008a75c>] show_stack+0x20/0x28
[   89.456756s][pid:1,cpu1,init][<ffffffc001153714>] dump_stack+0x84/0xa8
[   89.456787s][pid:1,cpu1,init][<ffffffc0000cfc5c>] __schedule_bug+0x88/0xdc
[   89.456817s][pid:1,cpu1,init][<ffffffc00115c4f0>] __schedule+0x714/0x854
[   89.456817s][pid:1,cpu1,init][<ffffffc00115c678>] schedule+0x48/0xa4
[   89.456817s][pid:1,cpu1,init][<ffffffc00115cbf0>] schedule_preempt_disabled+0x4c/0xf4
[   89.456848s][pid:1,cpu1,init][<ffffffc00115ea90>] __mutex_lock_slowpath+0xbc/0x1a4
[   89.456878s][pid:1,cpu1,init][<ffffffc00115ebd8>] mutex_lock+0x60/0x64
[   89.456878s][pid:1,cpu1,init][<ffffffc0006beb00>] ffs_func_eps_disable.isra.17+0x54/0x114
[   89.456909s][pid:1,cpu1,init][<ffffffc0006c05a4>] ffs_func_disable+0x30/0xa0
[   89.456909s][pid:1,cpu1,init][<ffffffc0006a6c4c>] reset_config.isra.8+0x44/0x78
[   89.456939s][pid:1,cpu1,init][<ffffffc0006a6dd8>] composite_disconnect+0x48/0xac
[   89.456939s][pid:1,cpu1,init][<ffffffc0006aafd4>] android_disconnect+0x48/0x54
[   89.456970s][pid:1,cpu1,init][<ffffffc0006ad9d0>] usb_gadget_remove_driver+0x58/0xa0
[   89.456970s][pid:1,cpu1,init][<ffffffc0006ada90>] usb_gadget_unregister_driver+0x78/0xc4

I checked the codes of composite_disconnect and found spin_lock_irqsave called before reset_config in which
ffs_func_eps_disable is called.

void composite_disconnect(struct usb_gadget *gadget)
{
        struct usb_composite_dev        *cdev = get_gadget_data(gadget);
        unsigned long                   flags;

        /* REVISIT:  should we have config and device level
         * disconnect callbacks?
         */
        spin_lock_irqsave(&cdev->lock, flags);
        if (cdev->config)
                reset_config(cdev);
        if (cdev->driver->disconnect)
                cdev->driver->disconnect(cdev);
        spin_unlock_irqrestore(&cdev->lock, flags);
}

static void ffs_func_eps_disable(struct ffs_function *func)
{
        struct ffs_ep *ep         = func->eps;
        struct ffs_epfile *epfile = func->ffs->epfiles;
        unsigned count            = func->ffs->eps_count;
        unsigned long flags;

        do {
                if (epfile)
                        mutex_lock(&epfile->mutex);
                spin_lock_irqsave(&func->ffs->eps_lock, flags);
                /* pending requests get nuked */
                if (likely(ep->ep))
                        usb_ep_disable(ep->ep);
                ++ep;
                spin_unlock_irqrestore(&func->ffs->eps_lock, flags);

                if (epfile) {
                        epfile->ep = NULL;
                        kfree(epfile->read_buffer);
                        epfile->read_buffer = NULL;
                        mutex_unlock(&epfile->mutex);
                        ++epfile;
                }
        } while (--count);
}

Should the epfile->read_buffer be cleared another place and the mutex_lock can be removed in ffs_func_eps_disable?

Thanks and Regards
Chen Yu