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priorityscore=1501 adultscore=0 phishscore=0 lowpriorityscore=0 impostorscore=0 spamscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609200039 On 9/20/26 10:48, Zhou, Yun wrote: > On 9/16/26 16:20, Ido Schimmel wrote: >> On Wed, Sep 16, 2026 at 02:13:14PM +0800, Yun Zhou wrote: >>> erspan_xmit() re-enters the network stack via ip_tunnel_xmit(), causing >>> nested acquisition of _xmit_lock on the underlay device while already >>> holding the ERSPAN device's _xmit_lock, creating an ABBA deadlock: >>> >>>    sch_direct_xmit [lock erspan] -> erspan_xmit -> ip_tunnel_xmit -> >>>    ip_output -> __dev_queue_xmit -> sch_direct_xmit [lock underlay] >>> >>> Set dev->lltx = true so HARD_TX_LOCK() skips the spinlock for ERSPAN. >>> This is safe as erspan_xmit() has no shared mutable state: o_seqno is >>> atomic, TX stats are per-CPU u64_stats, dst_cache is per-CPU, and >>> o_flags is no longer modified in the xmit path since commit 9958e69b9893 >>> ("gre: fix ERSPAN o_flags race/corruption in xmit and fill_info"). >>> GRETAP, the sibling device with identical xmit structure, already sets >>> lltx. >> >> In v3 I asked that the commit message: >> >> 1. State that the overlay and underlay devices should be of the same >> type (both erspan or both ip6erspan) for the splat to happen. >> > The devices do not need to be the same type. The actual syzbot report > [1] is between IPv4 erspan and vti6 - two completely different tunnel > types: > More precisely, any pair of 'locked + re-entering' tunnel devices whose underlying paths intersect could trigger this issue — for example, gre{6} (which previously didn't have lltx set correctly), and currently erspan{6}, vti6, etc. Same-type pairing is just one possible combination, not a requirement.