ifmedia status callback is non-sleepable

[Navdeep Parhar]

I think it's a bad idea in general for the kernel to be holding
non-sleepable locks around driver ioctls.

Regards,
Navdeep

On Thu, Jan 26, 2017 at 9:19 AM, Andrew Rybchenko <arybchik at freebsd.org> wrote:
> Hello,
>
> I'd like to double-check that it is intended/known limitation on ifmedia
> status callback to be non-sleepable.
> The limitation is imposed by usage of the ifmedia ioctl to get status from
> lacp/lagg code on port creation (it holds non-sleepable rm_wlock).
>
> Backtrace of the corresponding panic:
>
> Sleeping thread (tid 100578, pid 10653) owns a non-sleepable lock
> KDB: stack backtrace of thread 100578:
> #0 0xffffffff80ae46e2 at mi_switch+0xd2
> #1 0xffffffff80b31e6a at sleepq_wait+0x3a
> #2 0xffffffff80ae34e2 at _sx_xlock_hard+0x592
> #3 0xffffffff8222fd7e at sfxge_media_status+0x2e
> #4 0xffffffff80be7b90 at ifmedia_ioctl+0x170
> #5 0xffffffff8222c3d0 at sfxge_if_ioctl+0x1f0
> #6 0xffffffff82277fbe at lagg_port_ioctl+0xde
> #7 0xffffffff82278f9b at lacp_linkstate+0x4b
> #8 0xffffffff822794c2 at lacp_port_create+0x1e2
> #9 0xffffffff82276a73 at lagg_ioctl+0x1243
> #10 0xffffffff80bdcbec at ifioctl+0xfbc
> #11 0xffffffff80b41ab4 at kern_ioctl+0x2d4
> #12 0xffffffff80b41771 at sys_ioctl+0x171
> #13 0xffffffff80fa16ae at amd64_syscall+0x4ce
> #14 0xffffffff80f8442b at Xfast_syscall+0xfb
> panic: sleeping thread
> cpuid = 23
> KDB: stack backtrace:
> #0 0xffffffff80b24077 at kdb_backtrace+0x67
> #1 0xffffffff80ad93e2 at vpanic+0x182
> #2 0xffffffff80ad9253 at panic+0x43
> #3 0xffffffff80b39a99 at propagate_priority+0x299
> #4 0xffffffff80b3a59f at turnstile_wait+0x3ef
> #5 0xffffffff80ab493d at __mtx_lock_sleep+0x13d
> #6 0xffffffff80ad39f2 at _rm_wlock+0xb2
> #7 0xffffffff82275479 at lagg_port_setlladdr+0x29
> #8 0xffffffff80b363ca at taskqueue_run_locked+0x14a
> #9 0xffffffff80b361bf at taskqueue_run+0xbf
> #10 0xffffffff80a9340f at intr_event_execute_handlers+0x20f
> #11 0xffffffff80a93676 at ithread_loop+0xc6
> #12 0xffffffff80a90055 at fork_exit+0x85
> #13 0xffffffff80f8467e at fork_trampoline+0xe
>
> I think vnic driver has the problem as well since it grabs sx_lock from
> ifmedia status callback.
>
> Andrew.
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