Hi!

> >On Wed 2019-05-15 12:55:33, Greg Kroah-Hartman wrote:
> >> [ Upstream commit a8fd48b50deaa20808bbf0f6685f6f1acba6a64c ]
> >>
> >> Preemption disabled at:
> >>  [<ffff000008cabd54>] dev_set_rx_mode+0x1c/0x38
> >>  Call trace:
> >>  [<ffff00000808a5c0>] dump_backtrace+0x0/0x3d0
> >>  [<ffff00000808a9a4>] show_stack+0x14/0x20
> >>  [<ffff000008e6c0c0>] dump_stack+0xac/0xe4
> >>  [<ffff0000080fe76c>] ___might_sleep+0x164/0x238
> >>  [<ffff0000080fe890>] __might_sleep+0x50/0x88
> >>  [<ffff0000082261e4>] kmem_cache_alloc+0x17c/0x1d0
> >>  [<ffff000000ea0ae8>] ocelot_set_rx_mode+0x108/0x188
> >[mscc_ocelot_common]
> >>  [<ffff000008cabcf0>] __dev_set_rx_mode+0x58/0xa0
> >>  [<ffff000008cabd5c>] dev_set_rx_mode+0x24/0x38
> >>
> >> Fixes: a556c76adc05 ("net: mscc: Add initial Ocelot switch support")
> >
> >Is it right fix? Warning is gone, but now allocation is more likely to
> >fail, causing mc_add() to fail under memory pressure.
> >
> 
> So far this contributes to fixing a kernel hang issue, seen occasionally
> when the switch interfaces were brought up.
> Other than that I would look into improving this code.
> It looks suboptimal at least.  Do we really need to allocate whole
> struct netdev_hw_addr elements? Can the allocation size be reduced?
> What about pre-allocating enough room for ha elements outside the
> atomic context (set_rx_mode() in this case)?

Pre-allocating the elements sounds like a obvious solution, yes.

Best regards,
								Pavel
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