linux-kernel - Re: [PATCH v6.12] usbnet: Fix using smp_processor

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Message-ID: <574e390c-b6c7-4b7a-88e0-1166d17f6b34@oracle.com>
Date: Thu, 8 Jan 2026 18:52:31 +0530
From: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To: Rahul Sharma <black.hawk@....com>, gregkh@...uxfoundation.org,
        stable@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Zqiang <qiang.zhang@...ux.dev>,
        Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH v6.12] usbnet: Fix using smp_processor_id() in preemptible
 code warnings

Hi Rahul,
On 07/01/26 13:48, Rahul Sharma wrote:
> From: Zqiang <qiang.zhang@...ux.dev>
> 
> Syzbot reported the following warning:
> 
> BUG: using smp_processor_id() in preemptible [00000000] code: dhcpcd/2879
> caller is usbnet_skb_return+0x74/0x490 drivers/net/usb/usbnet.c:331
> CPU: 1 UID: 0 PID: 2879 Comm: dhcpcd Not tainted 6.15.0-rc4-syzkaller-00098-g615dca38c2ea #0 PREEMPT(voluntary)
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:94 [inline]
>   dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120
>   check_preemption_disabled+0xd0/0xe0 lib/smp_processor_id.c:49
>   usbnet_skb_return+0x74/0x490 drivers/net/usb/usbnet.c:331
>   usbnet_resume_rx+0x4b/0x170 drivers/net/usb/usbnet.c:708
>   usbnet_change_mtu+0x1be/0x220 drivers/net/usb/usbnet.c:417
>   __dev_set_mtu net/core/dev.c:9443 [inline]
>   netif_set_mtu_ext+0x369/0x5c0 net/core/dev.c:9496
>   netif_set_mtu+0xb0/0x160 net/core/dev.c:9520
>   dev_set_mtu+0xae/0x170 net/core/dev_api.c:247
>   dev_ifsioc+0xa31/0x18d0 net/core/dev_ioctl.c:572
>   dev_ioctl+0x223/0x10e0 net/core/dev_ioctl.c:821
>   sock_do_ioctl+0x19d/0x280 net/socket.c:1204
>   sock_ioctl+0x42f/0x6a0 net/socket.c:1311
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:906 [inline]
>   __se_sys_ioctl fs/ioctl.c:892 [inline]
>   __x64_sys_ioctl+0x190/0x200 fs/ioctl.c:892
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> For historical and portability reasons, the netif_rx() is usually
> run in the softirq or interrupt context, this commit therefore add
> local_bh_disable/enable() protection in the usbnet_resume_rx().
> 
> Fixes: 43daa96b166c ("usbnet: Stop RX Q on MTU change")
> Link: https://syzkaller.appspot.com/bug?id=81f55dfa587ee544baaaa5a359a060512228c1e1
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Zqiang <qiang.zhang@...ux.dev>
> Link: https://patch.msgid.link/20251011070518.7095-1-qiang.zhang@linux.dev
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> [ The context change is due to the commit 2c04d279e857
> ("net: usb: Convert tasklet API to new bottom half workqueue mechanism")
> in v6.17 which is irrelevant to the logic of this patch.]
> Signed-off-by: Rahul Sharma <black.hawk@....com>
> ---

Greg already queued this for 6.12.64: 
https://lore.kernel.org/all/20260106170510.964268694@linuxfoundation.org/

and 6.12.64 is now released. So I think we can skip this patch.

Also, if you want to figure this out without searching on lore. You 
could use stable-queue repo to see if a patch you are trying to backport 
is already being backported by someone else.

stable-queue repo: 
https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/

Thanks,
Harshit