When module is being initialized, __init() calls bus_register() and
driver_register().
These functions internally create various resources and sysfs files.
The sysfs files are used for basic operations(add/del device).
/sys/bus/netdevsim/new_device
/sys/bus/netdevsim/del_device

These sysfs files use netdevsim resources, they are mostly allocated
and initialized in ->probe() function, which is nsim_dev_probe().
But, sysfs files could be executed before ->probe() is finished.
So, accessing uninitialized data would occur.

Another problem is very similar.
/sys/bus/netdevsim/new_device internally creates sysfs files.
/sys/devices/netdevsim<id>/new_port
/sys/devices/netdevsim<id>/del_port

These sysfs files also use netdevsim resources, they are mostly allocated
and initialized in creating device routine, which is nsim_bus_dev_new().
But they also could be executed before nsim_bus_dev_new() is finished.
So, accessing uninitialized data would occur.

To fix these problems, this patch adds flags, which means whether the
operation is finished or not.
The flag variable 'nsim_bus_enable' means whether netdevsim bus was
initialized or not.
This is protected by nsim_bus_dev_list_lock.
The flag variable 'nsim_bus_dev->init' means whether nsim_bus_dev was
initialized or not.
This could be used in {new/del}_port_store() with no lock.

Test commands:
    #SHELL1
    modprobe netdevsim
    while :
    do
        echo "1 1" > /sys/bus/netdevsim/new_device
        echo "1 1" > /sys/bus/netdevsim/del_device
    done

    #SHELL2
    while :
    do
        echo 1 > /sys/devices/netdevsim1/new_port
        echo 1 > /sys/devices/netdevsim1/del_port
    done

Splat looks like:
[   47.508954][ T1008] general protection fault, probably for non-canonical address 0xdffffc0000000021: 0000 I
[   47.510793][ T1008] KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f]
[   47.511963][ T1008] CPU: 2 PID: 1008 Comm: bash Not tainted 5.5.0+ #322
[   47.512823][ T1008] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[   47.514041][ T1008] RIP: 0010:__mutex_lock+0x10a/0x14b0
[   47.514699][ T1008] Code: 08 84 d2 0f 85 7f 12 00 00 44 8b 0d 10 23 65 02 45 85 c9 75 29 49 8d 7f 68 48 b8 00 00 00 0f
[   47.517163][ T1008] RSP: 0018:ffff888059b4fbb0 EFLAGS: 00010206
[   47.517802][ T1008] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
[   47.518941][ T1008] RDX: 0000000000000021 RSI: ffffffff85926440 RDI: 0000000000000108
[   47.519732][ T1008] RBP: ffff888059b4fd30 R08: ffffffffc073fad0 R09: 0000000000000000
[   47.520729][ T1008] R10: ffff888059b4fd50 R11: ffff88804bb38040 R12: 0000000000000000
[   47.521702][ T1008] R13: dffffc0000000000 R14: ffffffff871976c0 R15: 00000000000000a0
[   47.522760][ T1008] FS:  00007fd4be05a740(0000) GS:ffff88806c800000(0000) knlGS:0000000000000000
[   47.523877][ T1008] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   47.524627][ T1008] CR2: 0000561c82b69cf0 CR3: 0000000065dd6004 CR4: 00000000000606e0
[   47.527662][ T1008] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   47.528604][ T1008] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   47.529531][ T1008] Call Trace:
[   47.529874][ T1008]  ? nsim_dev_port_add+0x50/0x150 [netdevsim]
[   47.530470][ T1008]  ? mutex_lock_io_nested+0x1380/0x1380
[   47.531018][ T1008]  ? _kstrtoull+0x76/0x160
[   47.531449][ T1008]  ? _parse_integer+0xf0/0xf0
[   47.531874][ T1008]  ? kernfs_fop_write+0x1cf/0x410
[   47.532330][ T1008]  ? sysfs_file_ops+0x160/0x160
[   47.532773][ T1008]  ? kstrtouint+0x86/0x110
[   47.533168][ T1008]  ? nsim_dev_port_add+0x50/0x150 [netdevsim]
[   47.533721][ T1008]  nsim_dev_port_add+0x50/0x150 [netdevsim]
[   47.534336][ T1008]  ? sysfs_file_ops+0x160/0x160
[   47.534858][ T1008]  new_port_store+0x99/0xb0 [netdevsim]
[   47.535439][ T1008]  ? del_port_store+0xb0/0xb0 [netdevsim]
[   47.536035][ T1008]  ? sysfs_file_ops+0x112/0x160
[   47.536544][ T1008]  ? sysfs_kf_write+0x3b/0x180
[   47.537029][ T1008]  kernfs_fop_write+0x276/0x410
[   47.537548][ T1008]  ? __sb_start_write+0x215/0x2e0
[   47.538110][ T1008]  vfs_write+0x197/0x4a0
[ ... ]

Fixes: f9d9db47 ("netdevsim: add bus attributes to add new and delete devices")
Fixes: 794b2c05 ("netdevsim: extend device attrs to support port addition and deletion")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>