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Date: Mon, 26 Feb 2024 11:04:51 +0800
From: Wen Gu <guwen@...ux.alibaba.com>
To: Wenjia Zhang <wenjia@...ux.ibm.com>, wintera@...ux.ibm.com,
hca@...ux.ibm.com, gor@...ux.ibm.com, agordeev@...ux.ibm.com,
davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, jaka@...ux.ibm.com, Gerd Bayer <gbayer@...ux.ibm.com>
Cc: borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
alibuda@...ux.alibaba.com, tonylu@...ux.alibaba.com,
linux-s390@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 06/15] net/smc: implement DMB-related operations
of loopback-ism
On 2024/2/23 22:12, Wenjia Zhang wrote:
>
>
> On 20.02.24 02:55, Wen Gu wrote:
>>
>>
>> On 2024/2/16 22:13, Wenjia Zhang wrote:
>>>
>>>
>>> On 11.01.24 13:00, Wen Gu wrote:
>>>> This implements DMB (un)registration and data move operations of
>>>> loopback-ism device.
>>>>
>>>> Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
>>>> ---
>>>> net/smc/smc_cdc.c | 6 ++
>>>> net/smc/smc_cdc.h | 1 +
>>>> net/smc/smc_loopback.c | 133 ++++++++++++++++++++++++++++++++++++++++-
>>>> net/smc/smc_loopback.h | 13 ++++
>>>> 4 files changed, 150 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/net/smc/smc_cdc.c b/net/smc/smc_cdc.c
>>>> index 3c06625ceb20..c820ef197610 100644
>>>> --- a/net/smc/smc_cdc.c
>>>> +++ b/net/smc/smc_cdc.c
>>>> @@ -410,6 +410,12 @@ static void smc_cdc_msg_recv(struct smc_sock *smc, struct smc_cdc_msg *cdc)
>>>> static void smcd_cdc_rx_tsklet(struct tasklet_struct *t)
>>>> {
>>>> struct smc_connection *conn = from_tasklet(conn, t, rx_tsklet);
>>>> +
>>>> + smcd_cdc_rx_handler(conn);
>>>> +}
>>>> +
>>>> +void smcd_cdc_rx_handler(struct smc_connection *conn)
>>>> +{
>>>> struct smcd_cdc_msg *data_cdc;
>>>> struct smcd_cdc_msg cdc;
>>>> struct smc_sock *smc;
>>>> diff --git a/net/smc/smc_cdc.h b/net/smc/smc_cdc.h
>>>> index 696cc11f2303..11559d4ebf2b 100644
>>>> --- a/net/smc/smc_cdc.h
>>>> +++ b/net/smc/smc_cdc.h
>>>> @@ -301,5 +301,6 @@ int smcr_cdc_msg_send_validation(struct smc_connection *conn,
>>>> struct smc_wr_buf *wr_buf);
>>>> int smc_cdc_init(void) __init;
>>>> void smcd_cdc_rx_init(struct smc_connection *conn);
>>>> +void smcd_cdc_rx_handler(struct smc_connection *conn);
>>>> #endif /* SMC_CDC_H */
>>>> diff --git a/net/smc/smc_loopback.c b/net/smc/smc_loopback.c
>>>> index 353d4a2d69a1..f72e7b24fc1a 100644
>>>> --- a/net/smc/smc_loopback.c
>>>> +++ b/net/smc/smc_loopback.c
>>>> @@ -15,11 +15,13 @@
>>>> #include <linux/types.h>
>>>> #include <net/smc.h>
>>>> +#include "smc_cdc.h"
>>>> #include "smc_ism.h"
>>>> #include "smc_loopback.h"
>>>> #if IS_ENABLED(CONFIG_SMC_LO)
>>>> #define SMC_LO_V2_CAPABLE 0x1 /* loopback-ism acts as ISMv2 */
>>>> +#define SMC_DMA_ADDR_INVALID (~(dma_addr_t)0)
>>>> static const char smc_lo_dev_name[] = "loopback-ism";
>>>> static struct smc_lo_dev *lo_dev;
>>>> @@ -50,6 +52,97 @@ static int smc_lo_query_rgid(struct smcd_dev *smcd, struct smcd_gid *rgid,
>>>> return 0;
>>>> }
>>>> +static int smc_lo_register_dmb(struct smcd_dev *smcd, struct smcd_dmb *dmb,
>>>> + void *client_priv)
>>>> +{
>>>> + struct smc_lo_dmb_node *dmb_node, *tmp_node;
>>>> + struct smc_lo_dev *ldev = smcd->priv;
>>>> + int sba_idx, order, rc;
>>>> + struct page *pages;
>>>> +
>>>> + /* check space for new dmb */
>>>> + for_each_clear_bit(sba_idx, ldev->sba_idx_mask, SMC_LO_MAX_DMBS) {
>>>> + if (!test_and_set_bit(sba_idx, ldev->sba_idx_mask))
>>>> + break;
>>>> + }
>>>> + if (sba_idx == SMC_LO_MAX_DMBS)
>>>> + return -ENOSPC;
>>>> +
>>>> + dmb_node = kzalloc(sizeof(*dmb_node), GFP_KERNEL);
>>>> + if (!dmb_node) {
>>>> + rc = -ENOMEM;
>>>> + goto err_bit;
>>>> + }
>>>> +
>>>> + dmb_node->sba_idx = sba_idx;
>>>> + order = get_order(dmb->dmb_len);
>>>> + pages = alloc_pages(GFP_KERNEL | __GFP_NOWARN |
>>>> + __GFP_NOMEMALLOC | __GFP_COMP |
>>>> + __GFP_NORETRY | __GFP_ZERO,
>>>> + order);
>>>> + if (!pages) {
>>>> + rc = -ENOMEM;
>>>> + goto err_node;
>>>> + }
>>>> + dmb_node->cpu_addr = (void *)page_address(pages);
>>>> + dmb_node->len = dmb->dmb_len;
>>>> + dmb_node->dma_addr = SMC_DMA_ADDR_INVALID;
>>>> +
>>>> +again:
>>>> + /* add new dmb into hash table */
>>>> + get_random_bytes(&dmb_node->token, sizeof(dmb_node->token));
>>>> + write_lock(&ldev->dmb_ht_lock);
>>>> + hash_for_each_possible(ldev->dmb_ht, tmp_node, list, dmb_node->token) {
>>>> + if (tmp_node->token == dmb_node->token) {
>>>> + write_unlock(&ldev->dmb_ht_lock);
>>>> + goto again;
>>>> + }
>>>> + }
>>>> + hash_add(ldev->dmb_ht, &dmb_node->list, dmb_node->token);
>>>> + write_unlock(&ldev->dmb_ht_lock);
>>>> +
>>> The write_lock_irqsave()/write_unlock_irqrestore() and read_lock_irqsave()/read_unlock_irqrestore()should be used
>>> instead of write_lock()/write_unlock() and read_lock()/read_unlock() in order to keep the lock irq-safe.
>>>
>>
>> dmb_ht_lock won't be hold in an interrupt or sockirq context. The dmb_{register|unregister},
>> dmb_{attach|detach} and data_move are all on the process context. So I think write_(un)lock
>> and read_(un)lock is safe here.
>
> right, it is not directly hold in a interrupt context, but it has a dependency on conn->send_lock as you wrote below,
> which requires irq-safe lock. And this matches our finding from a test:
>
> =====================================================
> WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
> 6.8.0-rc4-00787-g8eb4d2392609 #2 Not tainted
> -----------------------------------------------------
> smcapp/33802 [HC0[0]:SC0[2]:HE1:SE0] is trying to acquire:
> 00000000a2fc0330 (&ldev->dmb_ht_lock){++++}-{2:2}, at: smc_lo_move_data+0x84/0x1d0 [>
> and this task is already holding:
> 00000000e4df6f28 (&smc->conn.send_lock){+.-.}-{2:2}, at: smc_tx_sndbuf_nonempty+0xaa>
> which would create a new lock dependency:
> (&smc->conn.send_lock){+.-.}-{2:2} -> (&ldev->dmb_ht_lock){++++}-{2:2}
> but this new dependency connects a SOFTIRQ-irq-safe lock:
> (&smc->conn.send_lock){+.-.}-{2:2}
>
I understand, thank you Wenjia. I will fix it in the next version.
>>
>>>> + dmb->sba_idx = dmb_node->sba_idx;
>>>> + dmb->dmb_tok = dmb_node->token;
>>>> + dmb->cpu_addr = dmb_node->cpu_addr;
>>>> + dmb->dma_addr = dmb_node->dma_addr;
>>>> + dmb->dmb_len = dmb_node->len;
>>>> +
>>>> + return 0;
>>>> +
>>>> +err_node:
>>>> + kfree(dmb_node);
>>>> +err_bit:
>>>> + clear_bit(sba_idx, ldev->sba_idx_mask);
>>>> + return rc;
>>>> +}
>>>> +
>>>> +static int smc_lo_unregister_dmb(struct smcd_dev *smcd, struct smcd_dmb *dmb)
>>>> +{
>>>> + struct smc_lo_dmb_node *dmb_node = NULL, *tmp_node;
>>>> + struct smc_lo_dev *ldev = smcd->priv;
>>>> +
>>>> + /* remove dmb from hash table */
>>>> + write_lock(&ldev->dmb_ht_lock);
>>>> + hash_for_each_possible(ldev->dmb_ht, tmp_node, list, dmb->dmb_tok) {
>>>> + if (tmp_node->token == dmb->dmb_tok) {
>>>> + dmb_node = tmp_node;
>>>> + break;
>>>> + }
>>>> + }
>>>> + if (!dmb_node) {
>>>> + write_unlock(&ldev->dmb_ht_lock);
>>>> + return -EINVAL;
>>>> + }
>>>> + hash_del(&dmb_node->list);
>>>> + write_unlock(&ldev->dmb_ht_lock);
>>>> +
>>>> + clear_bit(dmb_node->sba_idx, ldev->sba_idx_mask);
>>>> + kfree(dmb_node->cpu_addr);
>>>> + kfree(dmb_node);
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> static int smc_lo_add_vlan_id(struct smcd_dev *smcd, u64 vlan_id)
>>>> {
>>>> return -EOPNOTSUPP;
>>>> @@ -76,6 +169,38 @@ static int smc_lo_signal_event(struct smcd_dev *dev, struct smcd_gid *rgid,
>>>> return 0;
>>>> }
>>>> +static int smc_lo_move_data(struct smcd_dev *smcd, u64 dmb_tok,
>>>> + unsigned int idx, bool sf, unsigned int offset,
>>>> + void *data, unsigned int size)
>>>> +{
>>>> + struct smc_lo_dmb_node *rmb_node = NULL, *tmp_node;
>>>> + struct smc_lo_dev *ldev = smcd->priv;
>>>> +
>>>> + read_lock(&ldev->dmb_ht_lock);
>>>> + hash_for_each_possible(ldev->dmb_ht, tmp_node, list, dmb_tok) {
>>>> + if (tmp_node->token == dmb_tok) {
>>>> + rmb_node = tmp_node;
>>>> + break;
>>>> + }
>>>> + }
>>>> + if (!rmb_node) {
>>>> + read_unlock(&ldev->dmb_ht_lock);
>>>> + return -EINVAL;
>>>> + }
>>>> + read_unlock(&ldev->dmb_ht_lock);
>>>> +
>>>> + memcpy((char *)rmb_node->cpu_addr + offset, data, size);
>>>> +
>>>
>>> Should this read_unlock be placed behind memcpy()?
>>>
>>
>> dmb_ht_lock is used to ensure safe access to the DMB hash table of loopback-ism.
>> The DMB hash table could be accessed by all the connections on loopback-ism, so
>> it should be protected.
>>
>> But a certain DMB is only used by one connection, and the move_data process is
>> protected by conn->send_lock (see smcd_tx_sndbuf_nonempty()), so the memcpy(rmb_node)
>> here is safe and no race with other.
>>
>> Thanks!
>>
> sounds reasonable.
>>> <...>
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