2023-03-08 19:09:45

by Breno Leitao

Subject: [PATCH] tcp: tcp_make_synack() can be called from process context

tcp_rtx_synack() now could be called in process context as explained in
0a375c822497 ("tcp: tcp_rtx_synack() can be called from process
context").

tcp_rtx_synack() might call tcp_make_synack(), which will touch per-CPU
variables with preemption enabled. This causes the following BUG:

BUG: using __this_cpu_add() in preemptible [00000000] code: ThriftIO1/5464
caller is tcp_make_synack+0x841/0xac0
Call Trace:
<TASK>
dump_stack_lvl+0x10d/0x1a0
check_preemption_disabled+0x104/0x110
tcp_make_synack+0x841/0xac0
tcp_v6_send_synack+0x5c/0x450
tcp_rtx_synack+0xeb/0x1f0
inet_rtx_syn_ack+0x34/0x60
tcp_check_req+0x3af/0x9e0
tcp_rcv_state_process+0x59b/0x2030
tcp_v6_do_rcv+0x5f5/0x700
release_sock+0x3a/0xf0
tcp_sendmsg+0x33/0x40
____sys_sendmsg+0x2f2/0x490
__sys_sendmsg+0x184/0x230
do_syscall_64+0x3d/0x90

Avoid calling __TCP_INC_STATS() with will touch per-cpu variables. Use
TCP_INC_STATS() which is safe to be called from context switch.

Fixes: 8336886f786f ("tcp: TCP Fast Open Server - support TFO listeners")
Signed-off-by: Breno Leitao <[email protected]>
---
net/ipv4/tcp_output.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 71d01cf3c13e..ba839e441450 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3605,7 +3605,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
th->window = htons(min(req->rsk_rcv_wnd, 65535U));
tcp_options_write(th, NULL, &opts);
th->doff = (tcp_header_size >> 2);
- __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
+ TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);

#ifdef CONFIG_TCP_MD5SIG
/* Okay, we have all we need - do the md5 hash if needed */
--
2.34.1

2023-03-09 13:38:11

by Eric Dumazet

Subject: Re: [PATCH] tcp: tcp_make_synack() can be called from process context

On Wed, Mar 8, 2023 at 8:07 PM Breno Leitao <[email protected]> wrote:
>
> tcp_rtx_synack() now could be called in process context as explained in
> 0a375c822497 ("tcp: tcp_rtx_synack() can be called from process
> context").
>
> tcp_rtx_synack() might call tcp_make_synack(), which will touch per-CPU
> variables with preemption enabled. This causes the following BUG:
>
>
> Avoid calling __TCP_INC_STATS() with will touch per-cpu variables. Use
> TCP_INC_STATS() which is safe to be called from context switch.
>
> Fixes: 8336886f786f ("tcp: TCP Fast Open Server - support TFO listeners")
> Signed-off-by: Breno Leitao <[email protected]>
>

This looks good to me, thanks !

Reviewed-by: Eric Dumazet <[email protected]>

2023-03-10 07:20:23

by patchwork-bot+netdevbpf

Subject: Re: [PATCH] tcp: tcp_make_synack() can be called from process context

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <[email protected]>:

On Wed, 8 Mar 2023 11:07:45 -0800 you wrote:
> tcp_rtx_synack() now could be called in process context as explained in
> 0a375c822497 ("tcp: tcp_rtx_synack() can be called from process
> context").
>
> tcp_rtx_synack() might call tcp_make_synack(), which will touch per-CPU
> variables with preemption enabled. This causes the following BUG:
>
> [...]

Here is the summary with links:
- tcp: tcp_make_synack() can be called from process context
https://git.kernel.org/netdev/net/c/bced3f7db95f

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html