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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
..
6lowpan net: replace ND_PRINTK with dynamic debug 2025-07-10 15:27:32 -07:00
9p Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
802 Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
8021q Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
appletalk Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
atm atm: lec: fix null-ptr-deref in lec_arp_clear_vccs 2026-02-28 09:33:26 -08:00
ax25 Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
batman-adv Here is a batman-adv bugfix: 2026-02-26 19:15:09 -08:00
bluetooth Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
bpf Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
bridge bridge: Check relevant per-VLAN options in VLAN range grouping 2026-02-26 19:24:29 -08:00
caif Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
can can: bcm: fix locking for bcm_op runtime updates 2026-03-02 10:24:40 +01:00
ceph Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
core net: Provide a PREEMPT_RT specific check for netdev_queue::_xmit_lock 2026-03-05 12:14:21 +01:00
dcb Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
devlink Convert 'alloc_flex' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
dns_resolver net/dns_resolver: use credential guards in dns_query() 2025-11-04 12:36:51 +01:00
dsa Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
ethernet net: optimize eth_type_trans() vs CONFIG_STACKPROTECTOR_STRONG=y 2025-11-24 19:27:31 -08:00
ethtool Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
handshake treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
hsr Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
ieee802154 Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
ife
ipv4 tcp: secure_seq: add back ports to TS offset 2026-03-04 17:44:35 -08:00
ipv6 tcp: secure_seq: add back ports to TS offset 2026-03-04 17:44:35 -08:00
iucv Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kcm kcm: fix zero-frag skb in frag_list on partial sendmsg error 2026-02-23 17:26:55 -08:00
key Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
l2tp Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
l3mdev net: fib_rules: Fix iif / oif matching on L3 master device 2025-04-15 17:54:56 -07:00
lapb treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
llc treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
mac80211 wifi: mac80211: fix missing ieee80211_eml_params member initialization 2026-03-03 08:37:29 +01:00
mac802154 Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
mctp Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
mpls Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
mptcp mptcp: pm: in-kernel: always mark signal+subflow endp as used 2026-03-04 18:21:13 -08:00
ncsi Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
netfilter Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
netlabel Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
netlink Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
netrom Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
nfc nfc: rawsock: cancel tx_work before socket teardown 2026-03-04 18:18:57 -08:00
nsh
openvswitch Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
packet Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
phonet treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
psample treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
psp Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
qrtr Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
rds net/rds: Fix circular locking dependency in rds_tcp_tune 2026-03-03 12:57:06 +01:00
rfkill Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
rose Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
rxrpc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
sched net_sched: sch_fq: clear q->band_pkt_count[] in fq_reset() 2026-03-04 17:54:22 -08:00
sctp Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
shaper Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
smc Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
strparser Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2025-11-13 12:35:38 -08:00
sunrpc Convert more 'alloc_obj' cases to default GFP_KERNEL arguments 2026-02-21 20:03:00 -08:00
switchdev treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
tipc Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
tls Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
unix net: annotate data-races around sk->sk_{data_ready,write_space} 2026-02-26 19:23:03 -08:00
vmw_vsock Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
wireless Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
x25 treewide: Replace kmalloc with kmalloc_obj for non-scalar types 2026-02-21 01:02:28 -08:00
xdp xsk: Fix zero-copy AF_XDP fragment drop 2026-02-28 08:55:11 -08:00
xfrm Including fixes from IPsec, Bluetooth and netfilter 2026-02-26 08:00:13 -08:00
compat.c socket: Unify getsockname and getpeername implementation 2025-11-26 13:45:23 -07:00
devres.c
Kconfig net: Kconfig: discourage drop_monitor enablement 2025-10-17 16:29:26 -07:00
Kconfig.debug
Makefile psp: base PSP device support 2025-09-18 12:32:06 +02:00
socket.c net: Drop the lock in skb_may_tx_timestamp() 2026-02-24 11:27:29 +01:00
sysctl_net.c