Re: [PATCH 01/12] netvm: Prevent a stream-specific deadlock

From: David Miller
Date: Fri May 11 2012 - 01:11:49 EST

From: Mel Gorman <mgorman@xxxxxxx>
Date: Thu, 10 May 2012 14:54:14 +0100

> It could happen that all !SOCK_MEMALLOC sockets have buffered so
> much data that we're over the global rmem limit. This will prevent
> SOCK_MEMALLOC buffers from receiving data, which will prevent userspace
> from running, which is needed to reduce the buffered data.
> Fix this by exempting the SOCK_MEMALLOC sockets from the rmem limit.
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>

This introduces an invariant which I am not so sure is enforced.

With this change it is absolutely required that once a socket
becomes SOCK_MEMALLOC it must never _ever_ lose that attribute.

Otherwise we can end up liberating global rmem tokens which we never
actually took.
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