netdev - Re: [PATCH net] bridge: use _bh spinlock variant for br_fdb

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Date:	Sun, 07 Jun 2015 15:25:33 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	nikolay@...ulusnetworks.com
Cc:	netdev@...r.kernel.org, wkok@...ulusnetworks.com,
	stephen@...workplumber.org
Subject: Re: [PATCH net] bridge: use _bh spinlock variant for br_fdb_update
 to avoid lockup

From: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Date: Fri,  5 Jun 2015 00:52:57 -0700

> From: Wilson Kok <wkok@...ulusnetworks.com>
> 
> br_fdb_update() can be called in process context in the following way:
> br_fdb_add() -> __br_fdb_add() -> br_fdb_update() (if NTF_USE flag is set)
> so we need to use spin_lock_bh because there are softirq users of the
> hash_lock. One easy way to reproduce this is to modify the bridge utility
> to set NTF_USE, enable stp and then set maxageing to a low value so
> br_fdb_cleanup() is called frequently and then just add new entries in
> a loop. This happens because br_fdb_cleanup() is called from timer/softirq
> context. These locks were _bh before commit f8ae737deea1
> ("[BRIDGE]: forwarding remove unneeded preempt and bh diasables")
> and at the time that commit was correct because br_fdb_update() couldn't be
> called from process context, but that changed after commit:
> 292d1398983f ("bridge: add NTF_USE support")
> 
> Signed-off-by: Wilson Kok <wkok@...ulusnetworks.com>
> Signed-off-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
> Fixes: 292d1398983f ("bridge: add NTF_USE support")

Applied and queued up for -stable, thanks Nik.
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