From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 11 Oct 2022 14:46:03 -0700

On Tue, Sep 20, 2022 at 12:00 PM [off-list ref] wrote:

quoted

Hello:

This series was applied to netdev/net-next.git (master)
by Jakub Kicinski [off-list ref]:

On Wed, 7 Sep 2022 18:10:16 -0700 you wrote:

quoted

The more sockets we have in the hash table, the longer we spend looking
up the socket.  While running a number of small workloads on the same
host, they penalise each other and cause performance degradation.

The root cause might be a single workload that consumes much more
resources than the others.  It often happens on a cloud service where
different workloads share the same computing resource.

[...]

Here is the summary with links:
  - [v6,net-next,1/6] tcp: Clean up some functions.
    https://git.kernel.org/netdev/net-next/c/08eaef904031
  - [v6,net-next,2/6] tcp: Don't allocate tcp_death_row outside of struct netns_ipv4.
    https://git.kernel.org/netdev/net-next/c/e9bd0cca09d1
  - [v6,net-next,3/6] tcp: Set NULL to sk->sk_prot->h.hashinfo.
    https://git.kernel.org/netdev/net-next/c/429e42c1c54e
  - [v6,net-next,4/6] tcp: Access &tcp_hashinfo via net.
    https://git.kernel.org/netdev/net-next/c/4461568aa4e5
  - [v6,net-next,5/6] tcp: Save unnecessary inet_twsk_purge() calls.
    https://git.kernel.org/netdev/net-next/c/edc12f032a5a
  - [v6,net-next,6/6] tcp: Introduce optional per-netns ehash.
    https://git.kernel.org/netdev/net-next/c/d1e5e6408b30

You are awesome, thank you!
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Note that this series is causing issues.

BUG: KASAN: use-after-free in tcp_or_dccp_get_hashinfo
include/net/inet_hashtables.h:181 [inline]
BUG: KASAN: use-after-free in reqsk_queue_unlink+0x320/0x350
net/ipv4/inet_connection_sock.c:913
Read of size 8 at addr ffff88807545bd80 by task syz-executor.2/8301

CPU: 1 PID: 8301 Comm: syz-executor.2 Not tainted
6.0.0-syzkaller-02757-gaf7d23f9d96a #0
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 09/22/2022
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:317 [inline]
print_report.cold+0x2ba/0x719 mm/kasan/report.c:433
kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
tcp_or_dccp_get_hashinfo include/net/inet_hashtables.h:181 [inline]
reqsk_queue_unlink+0x320/0x350 net/ipv4/inet_connection_sock.c:913
inet_csk_reqsk_queue_drop net/ipv4/inet_connection_sock.c:927 [inline]
inet_csk_reqsk_queue_drop_and_put net/ipv4/inet_connection_sock.c:939 [inline]
reqsk_timer_handler+0x724/0x1160 net/ipv4/inet_connection_sock.c:1053
call_timer_fn+0x1a0/0x6b0 kernel/time/timer.c:1474
expire_timers kernel/time/timer.c:1519 [inline]
__run_timers.part.0+0x674/0xa80 kernel/time/timer.c:1790
__run_timers kernel/time/timer.c:1768 [inline]
run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1803
__do_softirq+0x1d0/0x9c8 kernel/softirq.c:571
invoke_softirq kernel/softirq.c:445 [inline]
__irq_exit_rcu+0x123/0x180 kernel/softirq.c:650
irq_exit_rcu+0x5/0x20 kernel/softirq.c:662
sysvec_apic_timer_interrupt+0x93/0xc0 arch/x86/kernel/apic/apic.c:1107
</IRQ>

We forgot to make sure there were no TCP_NEW_SYN_RECV sockets in the
hash tables before deleting the hash tables.

Probably inet_twsk_purge() (when called when
et->ipv4.tcp_death_row.hashinfo->pernet is true)
also needs to remove all TCP_NEW_SYN_RECV request sockets.

Exactly, I'll do a quick test and post a fix.
Thank you for reporting!