netdev - Re: [PATCH net-next v2 4/4] nexthop: Fix splat with CONFIG_DEBUG

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Message-ID: <d3f29160-e44e-418e-967c-321b78ffc66b@kernel.org>
Date: Mon, 11 Mar 2024 21:28:54 -0600
From: David Ahern <dsahern@...nel.org>
To: Ido Schimmel <idosch@...dia.com>, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 edumazet@...gle.com, petrm@...dia.com
Subject: Re: [PATCH net-next v2 4/4] nexthop: Fix splat with
 CONFIG_DEBUG_PREEMPT=y

On 3/11/24 10:23 AM, Ido Schimmel wrote:
> Locally generated packets can increment the new nexthop statistics from
> process context, resulting in the following splat [1] due to preemption
> being enabled. Fix by using get_cpu_ptr() / put_cpu_ptr() which will
> which take care of disabling / enabling preemption.
> 
> BUG: using smp_processor_id() in preemptible [00000000] code: ping/949
> caller is nexthop_select_path+0xcf8/0x1e30
> CPU: 12 PID: 949 Comm: ping Not tainted 6.8.0-rc7-custom-gcb450f605fae #11
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc38 04/01/2014
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0xbd/0xe0
>  check_preemption_disabled+0xce/0xe0
>  nexthop_select_path+0xcf8/0x1e30
>  fib_select_multipath+0x865/0x18b0
>  fib_select_path+0x311/0x1160
>  ip_route_output_key_hash_rcu+0xe54/0x2720
>  ip_route_output_key_hash+0x193/0x380
>  ip_route_output_flow+0x25/0x130
>  raw_sendmsg+0xbab/0x34a0
>  inet_sendmsg+0xa2/0xe0
>  __sys_sendto+0x2ad/0x430
>  __x64_sys_sendto+0xe5/0x1c0
>  do_syscall_64+0xc5/0x1d0
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> [...]
> 
> Fixes: f4676ea74b85 ("net: nexthop: Add nexthop group entry stats")
> Signed-off-by: Ido Schimmel <idosch@...dia.com>
> ---
>  net/ipv4/nexthop.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 

Reviewed-by: David Ahern <dsahern@...nel.org>