On 2/8/26 9:14 AM, Michal Luczaj wrote:
On 2/7/26 23:00, Kuniyuki Iwashima wrote:
On Sat, Feb 7, 2026 at 6:35 AM Michal Luczaj <[email protected]> wrote:
This patch also happens to fix a deadlock that may occur when
bpf_iter_unix_seq_show()'s lock_sock_fast() takes the fast path and the
iter prog attempts to update a sockmap. Which ends up spinning at
sock_map_update_elem()'s bh_lock_sock():
Hmm.. this seems to be a more general problem for
bpf iter vs sockmap. bpf_iter_{tcp,udp}_seq_show() also
hold lock_sock(), where this patch's solution does not help.
We need to resolve this regardless of socket family.
I don't see any deadlocks there. Note that I've mentioned lock_sock_fast()
fast path was a problem, not lock_sock().
For the tcp/udp, I think the bpf_iter should be fine: lock_sock() in
seq_show and bh_lock_sock() in map_update. It seems redundant though.
From looking at may_update_sockmap(), other bpf progs (e.g., tc) can do
map_update also. On those paths, I am not sure why
sock_map_update_elem() does not need to check "!sock_owned_by_user(sk)".
If it is indeed an issue, it probably needs to be addressed separately.
It should also be helpful to be consistent with tcp/udp iter and use
lock_sock() instead of lock_sock_fast() in bpf_iter_unix_seq_show().
