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Liu Jian 0e2f1d93d2 net: let net.core.dev_weight always be non-zero 
[ Upstream commit d1f9f79fa2 ]

The following problem was encountered during stability test:

(NULL net_device): NAPI poll function process_backlog+0x0/0x530 \
	returned 1, exceeding its budget of 0.
------------[ cut here ]------------
list_add double add: new=ffff88905f746f48, prev=ffff88905f746f48, \
	next=ffff88905f746e40.
WARNING: CPU: 18 PID: 5462 at lib/list_debug.c:35 \
	__list_add_valid_or_report+0xf3/0x130
CPU: 18 UID: 0 PID: 5462 Comm: ping Kdump: loaded Not tainted 6.13.0-rc7+
RIP: 0010:__list_add_valid_or_report+0xf3/0x130
Call Trace:
? __warn+0xcd/0x250
? __list_add_valid_or_report+0xf3/0x130
enqueue_to_backlog+0x923/0x1070
netif_rx_internal+0x92/0x2b0
__netif_rx+0x15/0x170
loopback_xmit+0x2ef/0x450
dev_hard_start_xmit+0x103/0x490
__dev_queue_xmit+0xeac/0x1950
ip_finish_output2+0x6cc/0x1620
ip_output+0x161/0x270
ip_push_pending_frames+0x155/0x1a0
raw_sendmsg+0xe13/0x1550
__sys_sendto+0x3bf/0x4e0
__x64_sys_sendto+0xdc/0x1b0
do_syscall_64+0x5b/0x170
entry_SYSCALL_64_after_hwframe+0x76/0x7e

The reproduction command is as follows:
  sysctl -w net.core.dev_weight=0
  ping 127.0.0.1

This is because when the napi's weight is set to 0, process_backlog() may
return 0 and clear the NAPI_STATE_SCHED bit of napi->state, causing this
napi to be re-polled in net_rx_action() until __do_softirq() times out.
Since the NAPI_STATE_SCHED bit has been cleared, napi_schedule_rps() can
be retriggered in enqueue_to_backlog(), causing this issue.

Making the napi's weight always non-zero solves this problem.

Triggering this issue requires system-wide admin (setting is
not namespaced).

Fixes: e387660545 ("[NET]: Fix sysctl net.core.dev_weight")
Fixes: 3d48b53fb2 ("net: dev_weight: TX/RX orthogonality")
Signed-off-by: Liu Jian <liujian56@huawei.com>
Link: https://patch.msgid.link/20250116143053.4146855-1-liujian56@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-03-13 12:49:59 +01:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.