linux-kernel - Re: [PATCH] netxen: Fix a sleep-in-atomic bug in netxen_nic_pci_mem_access

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Message-Id: <20170620.133530.1607963470682255531.davem@davemloft.net>
Date:   Tue, 20 Jun 2017 13:35:30 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     baijiaju1990@....com
Cc:     manish.chopra@...ium.com, rahul.verma@...ium.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netxen: Fix a sleep-in-atomic bug in
 netxen_nic_pci_mem_access_direct

From: Jia-Ju Bai <baijiaju1990@....com>
Date: Mon, 19 Jun 2017 10:48:53 +0800

> The driver may sleep under a spin lock, and the function call path is:
> netxen_nic_pci_mem_access_direct (acquire the lock by spin_lock)
>   ioremap --> may sleep
> 
> To fix it, the lock is released before "ioremap", and the lock is 
> acquired again after this function.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>

This style of change you are making is really starting to be a
problem.

You can't just drop locks like this, especially without explaining
why it's ok, and why the mutual exclusion this code was trying to
achieve is still going to be OK afterwards.

In fact, I see zero analysis of the locking situation here, why
it was needed in the first place, and why your change is OK in
that context.

Any locking change is delicate, and you must put the greatest of
care and consideration into it.

Just putting "unlock/lock" around the sleeping operation shows a
very low level of consideration for the implications of the change
you are making.

This isn't like making whitespace fixes, sorry...