From: Arnd Bergmann <arnd@arndb.de>
Date: Sat, 30 Jan 2010 23:22:15 +0100

quoted

This is the fourth version of the macvtap driver,
based on the comments I got for the last version
I got a few days ago. Very few changes:

* release netdev in chardev open function so
  we can destroy it properly.
* Implement TUNSETSNDBUF
* fix sleeping call in rcu_read_lock
* Fix comment in namespace isolation patch
* Fix small context difference to make it apply
  to net-next

I can't really test here while travelling, so please
give it a go if you're interested in this driver.

I'm seeing complaints from might_sleep():

Feb  8 16:21:06 ti102 kernel: BUG: sleeping function called from
invalid context at include/linux/kernel.h:155
Feb  8 16:21:06 ti102 kernel: in_atomic(): 1, irqs_disabled(): 0, pid:
2881, name: qemu-kvm
Feb  8 16:21:06 ti102 kernel: Pid: 2881, comm: qemu-kvm Not tainted
2.6.29.6.Ar-224527.2009eswierk8 #1
Feb  8 16:21:06 ti102 kernel: Call Trace:
Feb  8 16:21:06 ti102 kernel: [<c0119250>] __might_sleep+0xdc/0xe3
Feb  8 16:21:06 ti102 kernel: [<c0210f7c>] copy_to_user+0x36/0x106
Feb  8 16:21:06 ti102 kernel: [<c02af568>] memcpy_toiovec+0x2c/0x50
Feb  8 16:21:06 ti102 kernel: [<c02afbb3>] skb_copy_datagram_iovec+0x47/0x184
Feb  8 16:21:06 ti102 kernel: [<c034bd07>] ? _spin_unlock_irqrestore+0x17/0x2c
Feb  8 16:21:06 ti102 kernel: [<f829a776>]
macvtap_aio_read+0x102/0x158 [macvtap]
Feb  8 16:21:06 ti102 kernel: [<c011eaf7>] ? default_wake_function+0x0/0xd
Feb  8 16:21:06 ti102 kernel: [<c016c75f>] do_sync_read+0xab/0xe9
Feb  8 16:21:06 ti102 kernel: [<c0133933>] ? autoremove_wake_function+0x0/0x33
Feb  8 16:21:06 ti102 kernel: [<c019211f>] ? eventfd_read+0x121/0x156
Feb  8 16:21:06 ti102 kernel: [<c011eaf7>] ? default_wake_function+0x0/0xd
Feb  8 16:21:06 ti102 kernel: [<c016d101>] vfs_read+0xb5/0x129
Feb  8 16:21:06 ti102 kernel: [<c016d20e>] sys_read+0x3b/0x60
Feb  8 16:21:06 ti102 kernel: [<c0102e71>] sysenter_do_call+0x12/0x25

Feb  8 16:21:08 ti102 kernel: BUG: sleeping function called from
invalid context at include/linux/kernel.h:155
Feb  8 16:21:08 ti102 kernel: in_atomic(): 1, irqs_disabled(): 0, pid:
2882, name: qemu-kvm
Feb  8 16:21:08 ti102 kernel: Pid: 2882, comm: qemu-kvm Not tainted
2.6.29.6.Ar-224527.2009eswierk8 #1
Feb  8 16:21:08 ti102 kernel: Call Trace:
Feb  8 16:21:08 ti102 kernel: [<c0119250>] __might_sleep+0xdc/0xe3
Feb  8 16:21:08 ti102 kernel: [<c0210e5f>] copy_from_user+0x34/0x11b
Feb  8 16:21:08 ti102 kernel: [<c02af388>] memcpy_fromiovec+0x2c/0x50
Feb  8 16:21:08 ti102 kernel: [<c02afa30>]
skb_copy_datagram_from_iovec+0x47/0x183
Feb  8 16:21:08 ti102 kernel: [<f829a618>]
macvtap_aio_write+0xaa/0x106 [macvtap]
Feb  8 16:21:08 ti102 kernel: [<c034a553>] ? mutex_unlock+0x8/0xa
Feb  8 16:21:08 ti102 kernel: [<c016c58d>] do_sync_readv_writev+0xa1/0xdf
Feb  8 16:21:08 ti102 kernel: [<c0133933>] ? autoremove_wake_function+0x0/0x33
Feb  8 16:21:08 ti102 kernel: [<c016c44f>] ? rw_copy_check_uvector+0x5b/0xc3
Feb  8 16:21:08 ti102 kernel: [<c016cbec>] do_readv_writev+0x82/0x165
Feb  8 16:21:08 ti102 kernel: [<f829a56e>] ?
macvtap_aio_write+0x0/0x106 [macvtap]
Feb  8 16:21:08 ti102 kernel: [<c0177461>] ? do_vfs_ioctl+0x4a3/0x4dc
Feb  8 16:21:08 ti102 kernel: [<c0112d83>] ? read_hpet+0xf/0x13
Feb  8 16:21:08 ti102 kernel: [<c016cd1e>] vfs_writev+0x4f/0x6b
Feb  8 16:21:08 ti102 kernel: [<c016cd75>] sys_writev+0x3b/0x60
Feb  8 16:21:08 ti102 kernel: [<c0102e71>] sysenter_do_call+0x12/0x25

I backported your patch to kernel 2.6.29.6, an i386 kernel with
CONFIG_PREEMPT=y and CONFIG_CLASSIC_RCU=y. It's entirely possible that
I screwed something up in the backport; I can post my modified patch
if it would help.

--Ed