[PATCH 3/3] nvme-tcp: fix I/O stalls on congested sockets

[Hannes Reinecke]

On 5/8/25 23:23, Kamaljit Singh wrote:
> Hi Hannes, Sagi,
> 
> On 5/7/25 15:26, Kamaljit Singh wrote:
>>> Can you please retest with the patchset '[PATCHv5 0/2] nvme-tcp: fixup
>>> I/O stall on congested sockets' _only_ ?
>>> (on top of nvme-6.16 latest, of course).
>>> I think I _should_ have included all the suggestions floating here,
>>> but we need to have confirmation.
>>
>> I've built the kernel against the latest of nvme-6.16 branch along with
>> these patches. Its with test now. Will let you know when we get some
>> results back.
>>
>> 0. [PATCHv5 0/2] nvme-tcp: fixup I/O stall on congested sockets - Apr 29, 01:18
>>      Hannes Reinecke (2):
>>        nvme-tcp: sanitize request list handling
>>        nvme-tcp: fix I/O stalls on congested sockets
>>
>> 1. [PATCH 1/2] nvme-tcp: sanitize request list handling - Apr 29, 02:31
>> 2. [PATCH 2/2] nvme-tcp: fix I/O stalls on congested sockets - Apr 29, 01:18
> IO timeouts are still occurring with Writes. The only Read that timed
> out was most likely due to the path error. It takes ~4.5 hours to fail.
> 
> However, this test does not fail if either ECN is off or if digests
> are not enabled. These passing combinations were run for 16+ hours
> without any issues. Both ECN and Header+Data Digests need to be turned
> on for it to fail.
> 
> Do you have a failing test as well? If so, is it quicker to cause the
> failure? Would you mind sharing any details?
> 
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 2 (f002) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 1 (2001) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 4 (c004) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: starting error recovery
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 15 (000f) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 6 (5006) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 3 (2003) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] block nvme1n3: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 8 (0008) type 4 opcode 0x2 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 14 (400e) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 13 (100d) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] block nvme1n4: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] block nvme1n4: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] block nvme1n4: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] block nvme1n2: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] block nvme1n4: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] block nvme1n2: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] block nvme1n2: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 5 (5005) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 7 (0007) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 11 (a00b) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] nvme nvme1: I/O tag 12 (f00c) type 4 opcode 0x1 (I/O Cmd) QID 4 timeout
>    [2025-05-07 19:57:13.295] block nvme1n1: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] block nvme1n1: no usable path - requeuing I/O
>    [2025-05-07 19:57:13.295] nvme nvme1: Reconnecting in 10 seconds...
> 
> In the current build I had these patches on top of the "nvme-6.16" branch:
>    41b2c90a51bd nvme-tcp: sanitize request list handling
>    9260acd6c230 nvme-tcp: fix I/O stalls on congested sockets
> 
Extremely wild guess: Can you try with this patch on top?

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 0e178115dc04..cdb8ea4eb467 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -1277,10 +1277,7 @@ static int nvme_tcp_try_send_ddgst(struct 
nvme_tcp_request *req)
                 .iov_len = NVME_TCP_DIGEST_LENGTH - req->offset
         };

-       if (nvme_tcp_queue_more(queue))
-               msg.msg_flags |= MSG_MORE;
-       else
-               msg.msg_flags |= MSG_EOR;
+       msg.msg_flags |= MSG_EOR;

         ret = kernel_sendmsg(queue->sock, &msg, &iov, 1, iov.iov_len);
         if (unlikely(ret <= 0))

It _could_ be that we're waiting in sendmsg() due to MSG_MORE, causing
these I/O timeouts as processing doesn't continue.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare at suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich