Re: [PATCH net-next 06/15] net/smc: implement DMB-related operations of loopback-ism

[Wen Gu <guwen@linux.alibaba.com>]

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@linux.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.
>>> <...>