ifmedia status callback is non-sleepable

[Andrew Rybchenko]

Navdeep, Gleb,

On 01/27/2017 10:37 PM, Gleb Smirnoff wrote:
>    Andrew,
>
> On Thu, Jan 26, 2017 at 08:24:43PM +0300, Andrew Rybchenko wrote:
> A> I'd like to double-check that it is intended/known limitation on ifmedia
> A> status callback to be non-sleepable.
> A> The limitation is imposed by usage of the ifmedia ioctl to get status
> A> from lacp/lagg code on port creation (it holds non-sleepable rm_wlock).
> A>
> A> Backtrace of the corresponding panic:
> A>
> A> Sleeping thread (tid 100578, pid 10653) owns a non-sleepable lock
> A> KDB: stack backtrace of thread 100578:
> A> #0 0xffffffff80ae46e2 at mi_switch+0xd2
> A> #1 0xffffffff80b31e6a at sleepq_wait+0x3a
> A> #2 0xffffffff80ae34e2 at _sx_xlock_hard+0x592
> A> #3 0xffffffff8222fd7e at sfxge_media_status+0x2e
> A> #4 0xffffffff80be7b90 at ifmedia_ioctl+0x170
> A> #5 0xffffffff8222c3d0 at sfxge_if_ioctl+0x1f0
> A> #6 0xffffffff82277fbe at lagg_port_ioctl+0xde
> A> #7 0xffffffff82278f9b at lacp_linkstate+0x4b
> A> #8 0xffffffff822794c2 at lacp_port_create+0x1e2
> A> #9 0xffffffff82276a73 at lagg_ioctl+0x1243
> A> #10 0xffffffff80bdcbec at ifioctl+0xfbc
> A> #11 0xffffffff80b41ab4 at kern_ioctl+0x2d4
> A> #12 0xffffffff80b41771 at sys_ioctl+0x171
> A> #13 0xffffffff80fa16ae at amd64_syscall+0x4ce
> A> #14 0xffffffff80f8442b at Xfast_syscall+0xfb
> A> panic: sleeping thread
> A> cpuid = 23
>
> I would say that this is bug in lagg(4). We shouldn't put constraint
> of non-sleepability for ioctl(2).

thanks a lot for replies. If so, what is the next step here? Should I 
submit a PR?

I can try to find time to fix it, but it highly depends on design and 
I'd be thankful if someone who knows it well suggests the design/idea.
Also I'm afraid i have very limited resources for testing any fixes in 
this area.

Andrew.