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

[Daniel Borkmann]

On 12/10/20 4:36 PM, Magnus Karlsson wrote:

From: Magnus Karlsson <magnus.karls...@intel.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.karls...@intel.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!