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1d856251a0
Fix a loop scenario of ethx:egress->ethx:egress
Example setup to reproduce:
tc qdisc add dev ethx root handle 1: drr
tc filter add dev ethx parent 1: protocol ip prio 1 matchall \
action mirred egress redirect dev ethx
Now ping out of ethx and you get a deadlock:
[ 116.892898][ T307] ============================================
[ 116.893182][ T307] WARNING: possible recursive locking detected
[ 116.893418][ T307] 6.18.0-rc6-01205-ge05021a829b8-dirty #204 Not tainted
[ 116.893682][ T307] --------------------------------------------
[ 116.893926][ T307] ping/307 is trying to acquire lock:
[ 116.894133][ T307] ffff88800c122908 (&sch->root_lock_key){+...}-{3:3}, at: __dev_queue_xmit+0x2210/0x3b50
[ 116.894517][ T307]
[ 116.894517][ T307] but task is already holding lock:
[ 116.894836][ T307] ffff88800c122908 (&sch->root_lock_key){+...}-{3:3}, at: __dev_queue_xmit+0x2210/0x3b50
[ 116.895252][ T307]
[ 116.895252][ T307] other info that might help us debug this:
[ 116.895608][ T307] Possible unsafe locking scenario:
[ 116.895608][ T307]
[ 116.895901][ T307] CPU0
[ 116.896057][ T307] ----
[ 116.896200][ T307] lock(&sch->root_lock_key);
[ 116.896392][ T307] lock(&sch->root_lock_key);
[ 116.896605][ T307]
[ 116.896605][ T307] *** DEADLOCK ***
[ 116.896605][ T307]
[ 116.896864][ T307] May be due to missing lock nesting notation
[ 116.896864][ T307]
[ 116.897123][ T307] 6 locks held by ping/307:
[ 116.897302][ T307] #0: ffff88800b4b0250 (sk_lock-AF_INET){+.+.}-{0:0}, at: raw_sendmsg+0xb20/0x2cf0
[ 116.897808][ T307] #1: ffffffff88c839c0 (rcu_read_lock){....}-{1:3}, at: ip_output+0xa9/0x600
[ 116.898138][ T307] #2: ffffffff88c839c0 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0x2c6/0x1ee0
[ 116.898459][ T307] #3: ffffffff88c83960 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x200/0x3b50
[ 116.898782][ T307] #4: ffff88800c122908 (&sch->root_lock_key){+...}-{3:3}, at: __dev_queue_xmit+0x2210/0x3b50
[ 116.899132][ T307] #5: ffffffff88c83960 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x200/0x3b50
[ 116.899442][ T307]
[ 116.899442][ T307] stack backtrace:
[ 116.899667][ T307] CPU: 2 UID: 0 PID: 307 Comm: ping Not tainted 6.18.0-rc6-01205-ge05021a829b8-dirty #204 PREEMPT(voluntary)
[ 116.899672][ T307] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[ 116.899675][ T307] Call Trace:
[ 116.899678][ T307] <TASK>
[ 116.899680][ T307] dump_stack_lvl+0x6f/0xb0
[ 116.899688][ T307] print_deadlock_bug.cold+0xc0/0xdc
[ 116.899695][ T307] __lock_acquire+0x11f7/0x1be0
[ 116.899704][ T307] lock_acquire+0x162/0x300
[ 116.899707][ T307] ? __dev_queue_xmit+0x2210/0x3b50
[ 116.899713][ T307] ? srso_alias_return_thunk+0x5/0xfbef5
[ 116.899717][ T307] ? stack_trace_save+0x93/0xd0
[ 116.899723][ T307] _raw_spin_lock+0x30/0x40
[ 116.899728][ T307] ? __dev_queue_xmit+0x2210/0x3b50
[ 116.899731][ T307] __dev_queue_xmit+0x2210/0x3b50
Fixes: 178ca30889 ("Revert "net/sched: Fix mirred deadlock on device recursion"")
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20251210162255.1057663-1-jhs@mojatatu.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>