linux.git/net/core/netpoll.c, branch v6.17

netpoll: prevent hanging NAPI when netcons gets enabled

2025-07-31T01:05:52+00:00

Paolo spotted hangs in NIPA running driver tests against virtio.
The tests hang in virtnet_close() -> virtnet_napi_tx_disable().

The problem is only reproducible if running multiple of our tests
in sequence (I used TEST_PROGS="xdp.py ping.py netcons_basic.sh \
netpoll_basic.py stats.py"). Initial suspicion was that this is
a simple case of double-disable of NAPI, but instrumenting the
code reveals:

 Deadlocked on NAPI ffff888007cd82c0 (virtnet_poll_tx):
   state: 0x37, disabled: false, owner: 0, listed: false, weight: 64

The NAPI was not in fact disabled, owner is 0 (rather than -1),
so the NAPI "thinks" it's scheduled for CPU 0 but it's not listed
(!list_empty(&n->poll_list) => false). It seems odd that normal NAPI
processing would wedge itself like this.

Better suspicion is that netpoll gets enabled while NAPI is polling,
and also grabs the NAPI instance. This confuses napi_complete_done():

  [netpoll]                                   [normal NAPI]
                                        napi_poll()
                                          have = netpoll_poll_lock()
                                            rcu_access_pointer(dev->npinfo)
                                              return NULL # no netpoll
                                          __napi_poll()
					    ->poll(->weight)
  poll_napi()
    cmpxchg(->poll_owner, -1, cpu)
      poll_one_napi()
        set_bit(NAPI_STATE_NPSVC, ->state)
                                              napi_complete_done()
                                                if (NAPIF_STATE_NPSVC)
                                                  return false
                                           # exit without clearing SCHED

This feels very unlikely, but perhaps virtio has some interactions
with the hypervisor in the NAPI ->poll that makes the race window
larger?

Best I could to to prove the theory was to add and trigger this
warning in napi_poll (just before netpoll_poll_unlock()):

      WARN_ONCE(!have && rcu_access_pointer(n->dev->npinfo) &&
                napi_is_scheduled(n) && list_empty(&n->poll_list),
                "NAPI race with netpoll %px", n);

If this warning hits the next virtio_close() will hang.

This patch survived 30 test iterations without a hang (without it
the longest clean run was around 10). Credit for triggering this
goes to Breno's recent netconsole tests.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Paolo Abeni 
Link: https://lore.kernel.org/c5a93ed1-9abe-4880-a3bb-8d1678018b1d@redhat.com
Acked-by: Jason Wang 
Reviewed-by: Xuan Zhuo 
Link: https://patch.msgid.link/20250726010846.1105875-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski

netpoll: move Ethernet setup to push_eth() helper

2025-07-08T01:52:56+00:00

Refactor Ethernet header population into dedicated function, completing
the layered abstraction with:

- push_eth() for link layer
- push_udp() for transport
- push_ipv4()/push_ipv6() for network

Signed-off-by: Breno Leitao 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20250702-netpoll_untagle_ip-v2-6-13cf3db24e2b@debian.org
Signed-off-by: Jakub Kicinski

netpoll: factor out UDP header setup into push_udp() helper

2025-07-08T01:52:56+00:00

Move UDP header construction from netpoll_send_udp() into a new
static helper function push_udp(). This completes the protocol
layer refactoring by:

1. Creating a dedicated helper for UDP header assembly
2. Removing UDP-specific logic from the main send function
3. Establishing a consistent pattern with existing IPv4/IPv6 helpers:
   - push_udp()
   - push_ipv4()
   - push_ipv6()

The change improves code organization and maintains the encapsulation
pattern established in previous refactorings.

Signed-off-by: Breno Leitao 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20250702-netpoll_untagle_ip-v2-5-13cf3db24e2b@debian.org
Signed-off-by: Jakub Kicinski

netpoll: factor out IPv4 header setup into push_ipv4() helper

2025-07-08T01:52:56+00:00

Move IPv4 header construction from netpoll_send_udp() into a new
static helper function push_ipv4(). This completes the refactoring
started with IPv6 header handling, creating symmetric helper functions
for both IP versions.

Changes include:
1. Extracting IPv4 header setup logic into push_ipv4()
2. Replacing inline IPv4 code with helper call
3. Moving eth assignment after helper calls for consistency

The refactoring reduces code duplication and improves maintainability
by isolating IP version-specific logic.

Signed-off-by: Breno Leitao 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20250702-netpoll_untagle_ip-v2-4-13cf3db24e2b@debian.org
Signed-off-by: Jakub Kicinski

netpoll: factor out IPv6 header setup into push_ipv6() helper

2025-07-08T01:52:55+00:00

Move IPv6 header construction from netpoll_send_udp() into a new
static helper function, push_ipv6(). This refactoring reduces code
duplication and improves readability in netpoll_send_udp().

Signed-off-by: Breno Leitao 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20250702-netpoll_untagle_ip-v2-3-13cf3db24e2b@debian.org
Signed-off-by: Jakub Kicinski

netpoll: factor out UDP checksum calculation into helper

2025-07-08T01:52:55+00:00

Extract UDP checksum calculation logic from netpoll_send_udp()
into a new static helper function netpoll_udp_checksum(). This
reduces code duplication and improves readability for both IPv4
and IPv6 cases.

No functional change intended.

Signed-off-by: Breno Leitao 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20250702-netpoll_untagle_ip-v2-2-13cf3db24e2b@debian.org
Signed-off-by: Jakub Kicinski

netpoll: Improve code clarity with explicit struct size calculations

2025-07-08T01:52:55+00:00

Replace pointer-dereference sizeof() operations with explicit struct names
for improved readability and maintainability. This change:

1. Replaces `sizeof(*udph)` with `sizeof(struct udphdr)`
2. Replaces `sizeof(*ip6h)` with `sizeof(struct ipv6hdr)`
3. Replaces `sizeof(*iph)` with `sizeof(struct iphdr)`

This will make it easy to move code in the upcoming patches.

No functional changes are introduced by this patch.

Signed-off-by: Breno Leitao 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20250702-netpoll_untagle_ip-v2-1-13cf3db24e2b@debian.org
Signed-off-by: Jakub Kicinski

Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

2025-06-26T17:40:50+00:00

Cross-merge networking fixes after downstream PR (net-6.16-rc4).

Conflicts:

Documentation/netlink/specs/mptcp_pm.yaml
  9e6dd4c256d0 ("netlink: specs: mptcp: replace underscores with dashes in names")
  ec362192aa9e ("netlink: specs: fix up indentation errors")
https://lore.kernel.org/20250626122205.389c2cd4@canb.auug.org.au

Adjacent changes:

Documentation/netlink/specs/fou.yaml
  791a9ed0a40d ("netlink: specs: fou: replace underscores with dashes in names")
  880d43ca9aa4 ("netlink: specs: clean up spaces in brackets")

Signed-off-by: Jakub Kicinski

net: netpoll: Initialize UDP checksum field before checksumming

2025-06-23T20:14:51+00:00

commit f1fce08e63fe ("netpoll: Eliminate redundant assignment") removed
the initialization of the UDP checksum, which was wrong and broke
netpoll IPv6 transmission due to bad checksumming.

udph->check needs to be set before calling csum_ipv6_magic().

Fixes: f1fce08e63fe ("netpoll: Eliminate redundant assignment")
Signed-off-by: Breno Leitao 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20250620-netpoll_fix-v1-1-f9f0b82bc059@debian.org
Signed-off-by: Jakub Kicinski

netpoll: Extract IPv6 address retrieval function

2025-06-19T23:15:35+00:00

Extract the IPv6 address retrieval logic from netpoll_setup() into
a dedicated helper function netpoll_take_ipv6() to improve code
organization and readability.

The function handles obtaining the local IPv6 address from the
network device, including proper address type matching between
local and remote addresses (link-local vs global), and includes
appropriate error handling when IPv6 is not supported or no
suitable address is available.

Signed-off-by: Breno Leitao 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20250618-netpoll_ip_ref-v1-3-c2ac00fe558f@debian.org
Signed-off-by: Jakub Kicinski