netdev - Re: [Patch net] tap: convert a mutex to a spinlock

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Message-Id: <20170706.105224.2248990091127065553.davem@davemloft.net>
Date:   Thu, 06 Jul 2017 10:52:24 +0100 (WEST)
From:   David Miller <davem@...emloft.net>
To:     xiyou.wangcong@...il.com
Cc:     netdev@...r.kernel.org, borntraeger@...ibm.com,
        sainath.grandhi@...el.com
Subject: Re: [Patch net] tap: convert a mutex to a spinlock

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Wed,  5 Jul 2017 13:50:00 -0700

> We are not allowed to block on the RCU reader side, so can't
> just hold the mutex as before. As a quick fix, convert it to
> a spinlock.
> 
> Fixes: d9f1f61c0801 ("tap: Extending tap device create/destroy APIs")
> Reported-by: Christian Borntraeger <borntraeger@...ibm.com>
> Cc: Sainath Grandhi <sainath.grandhi@...el.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

I agree with Eric that we should use idr_preload() and
idr_preload_end() here so that we can still use GFP_KERNEL even though
we're now using a spinlock instead of a mutex.