From: Hannes Frederic Sowa <redacted>
Date: Thu, 28 Mar 2013 20:10:50 +0100

On Thu, Mar 28, 2013 at 03:03:59PM -0400, David Miller wrote:

quoted

From: Hannes Frederic Sowa <redacted>
Date: Thu, 28 Mar 2013 19:57:21 +0100

quoted

On Wed, Mar 27, 2013 at 10:25:59AM -0700, Eric Dumazet wrote:

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On Wed, 2013-03-27 at 16:56 +0100, Jesper Dangaard Brouer wrote:

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This patch implements per hash bucket locking for the frag queue
hash.  This removes two write locks, and the only remaining write
lock is for protecting hash rebuild.  This essentially reduce the
readers-writer lock to a rebuild lock.

 ...

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I am not sure why you added _bh suffix to spin_lock()/spin_unlock()
here ?

I assume that it has to do with the usage of this code in
ipv6/netfilter/nf_conntrack_reasm.c, which could be invoked from process
context, if I read it correctly.

That appears to be the case yes.

That's an odd environment for these routines to be invoked from,
so longer term we should probably make the nf conntrack code do
the BH disabling around the inet frag calls, rather than make the
inet frag code eat the extra overhead for the more common invocations.

My idea was a bh-safe flag in struct inet_frags and conditionally use
spin_lock and spin_unlock_bh (these could be wrapped in inline functions just
for inet_fragment.c).

That's an extra check eaten by all users.  Really, put the overhead into
the call sites that need it, and nowhere else.