netdev - Re: [PATCH v4 bpf-next 2/4] bpf: add mmap() support for BPF_MAP_TYPE

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Date:   Fri, 15 Nov 2019 12:42:49 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v4 bpf-next 2/4] bpf: add mmap() support for
 BPF_MAP_TYPE_ARRAY

On Fri, 15 Nov 2019 08:36:56 -0800, Andrii Nakryiko wrote:
> Alternatively we can use spinlock. I don't think it's too ugly, tbh. See below.
> 
> From 0da495b911adad495857f1c0fc3596f1d06a705f Mon Sep 17 00:00:00 2001
> From: Andrii Nakryiko <andriin@...com>
> Date: Fri, 15 Nov 2019 08:32:43 -0800
> Subject: [PATCH bpf-next] bpf: switch freeze locking to use spin_lock and save
>  space
> 
> Switch to spin_lock in favor of mutex. Due to mmap-ing itself happening not
> under spinlock, there needs to be an extra "correction" step for writecnt, if
> mapping fails.

FWIW I was pondering that too, and thought your initial design was
nicer, the transient errors sometimes become a major PITA.