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linux/net/core
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Sebastian Andrzej Siewior b824c3e16c net: Provide a PREEMPT_RT specific check for netdev_queue::_xmit_lock 
After acquiring netdev_queue::_xmit_lock the number of the CPU owning
the lock is recorded in netdev_queue::xmit_lock_owner. This works as
long as the BH context is not preemptible.

On PREEMPT_RT the softirq context is preemptible and without the
softirq-lock it is possible to have multiple user in __dev_queue_xmit()
submitting a skb on the same CPU. This is fine in general but this means
also that the current CPU is recorded as netdev_queue::xmit_lock_owner.
This in turn leads to the recursion alert and the skb is dropped.

Instead checking the for CPU number, that owns the lock, PREEMPT_RT can
check if the lockowner matches the current task.

Add netif_tx_owned() which returns true if the current context owns the
lock by comparing the provided CPU number with the recorded number. This
resembles the current check by negating the condition (the current check
returns true if the lock is not owned).
On PREEMPT_RT use rt_mutex_owner() to return the lock owner and compare
the current task against it.
Use the new helper in __dev_queue_xmit() and netif_local_xmit_active()
which provides a similar check.
Update comments regarding pairing READ_ONCE().

Reported-by: Bert Karwatzki <spasswolf@web.de>
Closes: https://lore.kernel.org/all/20260216134333.412332-1-spasswolf@web.de
Fixes: 3253cb49cb ("softirq: Allow to drop the softirq-BKL lock on PREEMPT_RT")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reported-by: Bert Karwatzki <spasswolf@web.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20260302162631.uGUyIqDT@linutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
2026-03-05 12:14:21 +01:00
..
bpf_sk_storage.c Convert 'alloc_flex' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
datagram.c net: datagram: introduce datagram_poll_queue for custom receive queues 2025-10-23 15:46:04 +02:00
dev.c net: Provide a PREEMPT_RT specific check for netdev_queue::_xmit_lock 2026-03-05 12:14:21 +01:00
dev.h net: add queue config validation callback 2026-01-23 11:49:02 -08:00
dev_addr_lists.c net: s/dev_pre_changeaddr_notify/netif_pre_changeaddr_notify/ 2025-07-18 17:27:47 -07:00
dev_addr_lists_test.c net: dev_addr_lists: move locking out of init/exit in kunit 2024-04-15 10:26:35 +01:00
dev_api.c net: define an enum for the napi threaded state 2025-07-24 18:34:55 -07:00
dev_ioctl.c net: remove legacy way to get/set HW timestamp config 2026-01-20 18:21:27 -08:00
devmem.c net: devmem: use READ_ONCE/WRITE_ONCE on binding->dev 2026-03-04 17:59:27 -08:00
devmem.h net: inline net_is_devmem_iov() 2026-01-25 13:18:53 -08:00
drop_monitor.c Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
dst.c treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
dst_cache.c net: dst: annotate data-races around dst->obsolete 2025-07-02 14:32:29 -07:00
failover.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
fib_notifier.c net: do not acquire rtnl in fib_seq_sum() 2024-10-11 15:35:05 -07:00
fib_rules.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-04-17 12:26:50 -07:00
filter.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
flow_dissector.c net: remove '__' from __skb_flow_get_ports() 2025-02-24 14:27:53 -08:00
flow_offload.c Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
gen_estimator.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
gen_stats.c
gro.c net/ipv6: Drop HBH for BIG TCP on RX side 2026-02-06 20:50:12 -08:00
gro_cells.c treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
gso.c net: introduce struct net_hotdata 2024-03-07 21:12:41 -08:00
hotdata.c net: add net.core.qdisc_max_burst 2026-01-13 10:12:11 +01:00
hwbm.c
ieee8021q_helpers.c net: ieee8021q: fix insufficient table-size assertion 2025-07-01 12:55:49 +02:00
link_watch.c linkwatch: use __dev_put() in callers to prevent UAF 2026-02-02 16:59:18 -08:00
lock_debug.c netdev: fix the locking for netdev notifications 2025-04-17 18:55:14 -07:00
lwt_bpf.c ipv4: Convert ->flowi4_tos to dscp_t. 2025-08-26 17:34:31 -07:00
lwtunnel.c inet: Remove rtnl_is_held arg of lwtunnel_valid_encap_type(_attr)?(). 2025-05-20 19:18:24 -07:00
Makefile net: get rid of net/core/request_sock.c 2026-02-05 09:23:05 -08:00
mp_dmabuf_devmem.h memory-provider: dmabuf devmem memory provider 2024-09-11 20:44:31 -07:00
neighbour.c treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
net-procfs.c net: add proper RCU protection to /proc/net/ptype 2026-02-03 19:20:30 -08:00
net-sysfs.c net: Keep ignoring isolated cpuset change 2026-02-03 15:23:33 +01:00
net-sysfs.h net: remove RTNL use for /proc/sys/net/core/rps_default_mask 2025-07-07 18:42:12 -07:00
net-traces.c move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
net_namespace.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
net_test.c pfcp: always set pfcp metadata 2024-04-01 10:49:28 +01:00
netclassid_cgroup.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
netdev-genl-gen.c Revert "Merge branch 'netkit-support-for-io_uring-zero-copy-and-af_xdp'" 2026-01-20 18:06:01 -08:00
netdev-genl-gen.h Revert "Merge branch 'netkit-support-for-io_uring-zero-copy-and-af_xdp'" 2026-01-20 18:06:01 -08:00
netdev-genl.c Revert "Merge branch 'netkit-support-for-io_uring-zero-copy-and-af_xdp'" 2026-01-20 18:06:01 -08:00
netdev_config.c net: add queue config validation callback 2026-01-23 11:49:02 -08:00
netdev_queues.c Revert "Merge branch 'netkit-support-for-io_uring-zero-copy-and-af_xdp'" 2026-01-20 18:06:01 -08:00
netdev_rx_queue.c net: add queue config validation callback 2026-01-23 11:49:02 -08:00
netevent.c
netmem_priv.h netmem: replace __netmem_clear_lsb() with netmem_to_nmdesc() 2025-10-14 13:37:26 +02:00
netpoll.c net: Provide a PREEMPT_RT specific check for netdev_queue::_xmit_lock 2026-03-05 12:14:21 +01:00
netprio_cgroup.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
of_net.c
page_pool.c net: page_pool: sanitise allocation order 2025-12-02 11:08:39 -08:00
page_pool_priv.h net: page_pool: don't try to stash the napi id 2025-01-27 14:37:41 -08:00
page_pool_user.c net: use napi_id_valid helper 2025-02-17 16:43:04 -08:00
pktgen.c kernel.h: drop hex.h and update all hex.h users 2026-01-20 19:44:19 -08:00
ptp_classifier.c
rtnetlink.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
scm.c treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
secure_seq.c tcp: secure_seq: add back ports to TS offset 2026-03-04 17:44:35 -08:00
selftests.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
skb_fault_injection.c net: Implement fault injection forcing skb reallocation 2024-11-12 12:05:33 +01:00
skbuff.c net: Drop the lock in skb_may_tx_timestamp() 2026-02-24 11:27:29 +01:00
skmsg.c net: annotate data-races around sk->sk_{data_ready,write_space} 2026-02-26 19:23:03 -08:00
sock.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
sock_destructor.h
sock_diag.c treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
sock_map.c treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
sock_reuseport.c treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
stream.c net: stream: add description for sk_stream_write_space() 2025-07-18 16:57:21 -07:00
sysctl_net_core.c net: include <linux/hex.h> from sysctl_net_core.c 2026-01-26 16:35:53 -08:00
timestamping.c net: Add the possibility to support a selected hwtstamp in netdevice 2024-12-16 12:51:40 +00:00
tso.c move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
utils.c kernel.h: drop hex.h and update all hex.h users 2026-01-20 19:44:19 -08:00
xdp.c Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00