netdev - Re: [PATCH net-next] net: disable preemption in dev_core_stats_XXX

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Date:   Mon, 14 Mar 2022 11:32:27 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        jeffreyji <jeffreyji@...gle.com>,
        Brian Vazquez <brianvv@...gle.com>
Subject: Re: [PATCH net-next] net: disable preemption in
 dev_core_stats_XXX_inc() helpers

On Sat, 2022-03-12 at 13:45 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> syzbot was kind enough to remind us that dev->{tx_dropped|rx_dropped}
> could be increased in process context.
> 
> BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor413/3593
> caller is netdev_core_stats_alloc+0x98/0x110 net/core/dev.c:10298
> CPU: 1 PID: 3593 Comm: syz-executor413 Not tainted 5.17.0-rc7-syzkaller-02426-g97aeb877de7f #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
>  check_preemption_disabled+0x16b/0x170 lib/smp_processor_id.c:49
>  netdev_core_stats_alloc+0x98/0x110 net/core/dev.c:10298
>  dev_core_stats include/linux/netdevice.h:3855 [inline]
>  dev_core_stats_rx_dropped_inc include/linux/netdevice.h:3866 [inline]
>  tun_get_user+0x3455/0x3ab0 drivers/net/tun.c:1800
>  tun_chr_write_iter+0xe1/0x200 drivers/net/tun.c:2015
>  call_write_iter include/linux/fs.h:2074 [inline]
>  new_sync_write+0x431/0x660 fs/read_write.c:503
>  vfs_write+0x7cd/0xae0 fs/read_write.c:590
>  ksys_write+0x12d/0x250 fs/read_write.c:643
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7f2cf4f887e3
> Code: 5d 41 5c 41 5d 41 5e e9 9b fd ff ff 66 2e 0f 1f 84 00 00 00 00 00 90 64 8b 04 25 18 00 00 00 85 c0 75 14 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 55 c3 0f 1f 40 00 48 83 ec 28 48 89 54 24 18
> RSP: 002b:00007ffd50dd5fd8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00007ffd50dd6000 RCX: 00007f2cf4f887e3
> RDX: 000000000000002a RSI: 0000000000000000 RDI: 00000000000000c8
> RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007ffd50dd5ff0 R14: 00007ffd50dd5fe8 R15: 00007ffd50dd5fe4
>  </TASK>
> 
> Fixes: 625788b58445 ("net: add per-cpu storage and net->core_stats")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: jeffreyji <jeffreyji@...gle.com>
> Cc: Brian Vazquez <brianvv@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> ---
>  include/linux/netdevice.h | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 0d994710b3352395b8c6d6fd53affb2fe0cea39f..8cbe96ce0a2cd9e4f02168835d460d1c91901430 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -3858,10 +3858,14 @@ static inline struct net_device_core_stats *dev_core_stats(struct net_device *de
>  #define DEV_CORE_STATS_INC(FIELD)						\
>  static inline void dev_core_stats_##FIELD##_inc(struct net_device *dev)		\
>  {										\
> -	struct net_device_core_stats *p = dev_core_stats(dev);			\
> +	struct net_device_core_stats *p;					\
> +										\
> +	preempt_disable();							\
> +	p = dev_core_stats(dev);						\
>  										\
>  	if (p)									\
>  		local_inc(&p->FIELD);						\
> +	preempt_enable();							\
>  }
>  DEV_CORE_STATS_INC(rx_dropped)
>  DEV_CORE_STATS_INC(tx_dropped)

LGTM, thanks Eric!

Acked-by: Paolo Abeni <pabeni@...hat.com>