netdev - Re: [PATCH 0/6] ravb/sh_eth: fix sleep in atomic by reusing shared ethtool handlers

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Date:   Thu, 24 May 2018 20:24:08 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH 0/6] ravb/sh_eth: fix sleep in atomic by reusing shared
 ethtool handlers

On 05/24/2018 07:40 PM, Sergei Shtylyov wrote:

>> For ages trivial changes to RAVB and SuperH ethernet links by means of
>> standard 'ethtool' trigger a 'sleeping function called from invalid
>> context' bug, to visualize it on r8a7795 ULCB:
>>
>>   % ethtool -r eth0
>>   BUG: sleeping function called from invalid context at kernel/locking/mutex.c:747
>>   in_atomic(): 1, irqs_disabled(): 128, pid: 554, name: ethtool
>>   INFO: lockdep is turned off.
>>   irq event stamp: 0
>>   hardirqs last  enabled at (0): [<0000000000000000>]           (null)
>>   hardirqs last disabled at (0): [<ffff0000080e1d3c>] copy_process.isra.7.part.8+0x2cc/0x1918
>>   softirqs last  enabled at (0): [<ffff0000080e1d3c>] copy_process.isra.7.part.8+0x2cc/0x1918
>>   softirqs last disabled at (0): [<0000000000000000>]           (null)
>>   CPU: 5 PID: 554 Comm: ethtool Not tainted 4.17.0-rc4-arm64-renesas+ #33
>>   Hardware name: Renesas H3ULCB board based on r8a7795 ES2.0+ (DT)
>>   Call trace:
>>    dump_backtrace+0x0/0x198
>>    show_stack+0x24/0x30
>>    dump_stack+0xb8/0xf4
>>    ___might_sleep+0x1c8/0x1f8
>>    __might_sleep+0x58/0x90
>>    __mutex_lock+0x50/0x890
>>    mutex_lock_nested+0x3c/0x50
>>    phy_start_aneg_priv+0x38/0x180
>>    phy_start_aneg+0x24/0x30
>>    ravb_nway_reset+0x3c/0x68
>>    dev_ethtool+0x3dc/0x2338
>>    dev_ioctl+0x19c/0x490
>>    sock_do_ioctl+0xe0/0x238
>>    sock_ioctl+0x254/0x460
>>    do_vfs_ioctl+0xb0/0x918
>>    ksys_ioctl+0x50/0x80
>>    sys_ioctl+0x34/0x48
>>    __sys_trace_return+0x0/0x4
>>
>> The root cause is that an attempt to modify ECMR and GECMR registers
>> only when RX/TX function is disabled was too overcomplicated in its
>> original implementation, also processing of an optional Link Change
>> interrupt added even more complexity, as a result the implementation
>> was error prone.
>>
>> The new locking scheme is confirmed to be correct by dumping driver
>> specific and generic PHY framework function calls with aid of ftrace
>> while running more or less advanced tests.
>>
>> Please note that sh_eth patches from the series were built-tested only.
>>
>> On purpose I do not add Fixes tags, the reused PHY handlers were added
>> way later than the fixed problems were firstly found in the drivers.
> 
>    I think you went one step too far with these fixes. On the first glance,
> the real fixes are to remove grabbing/releasing the spinlock for the duration
> of the phylib calls. Am I right? If so, making use of the new phylib APIs
> would be a further enhancement, it's not needed for fixing the splats per se...

   Note that I hadn't looked at the patches #3/#6 at the time of writing this;
those seem to be more complicated than the rest.

MBR, Sergei