Re: iw scan hangs in netlink ENOBUFS loop with kernel 6.6.99+

On 7/14/26 00:37, Peter Astrand wrote:
> 
> kernel 6.6.y
> iw 6.7
> libnl-genl-3-200 3.9.0
> mac80211_hwsim
> 
> With kernel 6.6.99 and later, "iw dev <device> scan" sometimes hangs in 
> busy loop:

Thanks for the report. We need to rule out if this is a 6.6.y specific
problem (like a broken or incomplete backport) or something general.
Could you please check if 7.2-rc is affected as well? Testing 6.18.y
might help, too, if it's easy for you to try. Maybe switching to that
might be the easies way to resolve the problem and a good idea in
general, as explained here:
http://www.kroah.com/log/blog/2018/08/24/what-stable-kernel-should-i-use/

Ciao, Thorsten
> recvmsg(3, {msg_namelen=12}, 0)         = -1 ENOBUFS (No buffer space available)
> recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 
> msg_namelen=12, msg_iov=[{iov_base=[{nlmsg_len=48, nlmsg_type=NLMSG_ERROR, 
> nlmsg_flags=0, nlmsg_seq=2511084235, nlmsg_pid=-1866444344}, 
> {error=-ENOBUFS, msg=[{nlmsg_len=28, nlmsg_type=0x18 /* NLMSG_??? */, 
> nlmsg_flags=NLM_F_REQUEST|NLM_F_ACK|0x300, nlmsg_seq=2511084235, 
> nlmsg_pid=-1866444344}, 
> "\x20\x00\x00\x00\x08\x00\x03\x00\x0e\x00\x00\x00"]}], iov_len=16384}], 
> msg_iovlen=1, msg_controllen=0, msg_flags=0}, MSG_PEEK|MSG_TRUNC) = 48
> 
> This issue appears with kernel 6.6.99 and later, even latest version 
> 6.6.144. 
> 
> If I revert these commits:
> 
> 346c820ef513 netlink: avoid infinite retry looping in netlink_unicast()
> c31ee1695b6d netlink: make sure we allow at least one dump skb
> ce2ac2e46719 netlink: Fix rmem check in netlink_broadcast_deliver().
> 55baecb9eb90 netlink: Fix wraparounds of sk->sk_rmem_alloc.
> 
> ...then 6.6.144 works fine as well. Seems like there is a regression here. 
> Any ideas? 
> 
> Br,
> Peter Astrand
>