RE: [PATCH 4.19 042/113] ocelot: Dont sleep in atomic context (irqs_disabled())

[Claudiu Manoil]

>-----Original Message-----
>From: Pavel Machek <pavel@xxxxxxx>
>Sent: Friday, May 17, 2019 11:17 AM
>To: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>Cc: linux-kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx; Claudiu Manoil
><claudiu.manoil@xxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>; Sasha
>Levin <sashal@xxxxxxxxxx>
>Subject: Re: [PATCH 4.19 042/113] ocelot: Dont sleep in atomic context
>(irqs_disabled())
>
>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)?

Thanks,
Claudiu