netdev - Re: [PATCH bpf-next] samples/bpf: fix possible hang in xdpsock with multiple threads

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Message-ID: <a41f3859-e541-3fba-9b8b-874da86de92d@iogearbox.net>
Date:   Thu, 10 Dec 2020 17:03:00 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Magnus Karlsson <magnus.karlsson@...il.com>,
        magnus.karlsson@...el.com, bjorn.topel@...el.com, ast@...nel.org,
        netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, jonathan.lemon@...il.com,
        maciej.fijalkowski@...el.com, maciejromanfijalkowski@...il.com
Subject: Re: [PATCH bpf-next] samples/bpf: fix possible hang in xdpsock with
 multiple threads

On 12/10/20 4:36 PM, Magnus Karlsson wrote:
> From: Magnus Karlsson <magnus.karlsson@...el.com>
> 
> Fix a possible hang in xdpsock that can occur when using multiple
> threads. In this case, one or more of the threads might get stuck in
> the while-loop in tx_only after the user has signaled the main thread
> to stop execution. In this case, no more Tx packets will be sent, so a
> thread might get stuck in the aforementioned while-loop. Fix this by
> introducing a test inside the while-loop to check if the benchmark has
> been terminated. If so, exit the loop.
> 
> Fixes: cd9e72b6f210 ("samples/bpf: xdpsock: Add option to specify batch size")
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>

With the patch applied, I'm getting a new warning:

   CC  /home/darkstar/trees/bpf-next/samples/bpf/xdpsock_user.o
/home/darkstar/trees/bpf-next/samples/bpf/xdpsock_user.c: In function ‘main’:
/home/darkstar/trees/bpf-next/samples/bpf/xdpsock_user.c:1272:6: warning: ‘idx’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  1272 |  u32 idx;
       |      ^~~

Previously compiling w/o issues:

  [...]
   CC  /home/darkstar/trees/bpf-next/samples/bpf/xdpsock_ctrl_proc.o
   CC  /home/darkstar/trees/bpf-next/samples/bpf/xdpsock_user.o
   CC  /home/darkstar/trees/bpf-next/samples/bpf/xsk_fwd.o
   LD  /home/darkstar/trees/bpf-next/samples/bpf/fds_example
  [...]

For testing, I used:

   gcc --version
   gcc (GCC) 9.0.1 20190312 (Red Hat 9.0.1-0.10)

Ptal, thx!