netdev - Re: [RFC net-next 03/17] net/smc: Remove error handling of unregister

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Message-ID: <aJh8d2G9-veAynO1@linux.alibaba.com>
Date: Sun, 10 Aug 2025 19:03:19 +0800
From: Dust Li <dust.li@...ux.alibaba.com>
To: Alexandra Winter <wintera@...ux.ibm.com>,
	David Miller <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"D. Wythe" <alibuda@...ux.alibaba.com>,
	Sidraya Jayagond <sidraya@...ux.ibm.com>,
	Wenjia Zhang <wenjia@...ux.ibm.com>,
	Julian Ruess <julianr@...ux.ibm.com>
Cc: netdev@...r.kernel.org, linux-s390@...r.kernel.org,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Thorsten Winkler <twinkler@...ux.ibm.com>,
	Simon Horman <horms@...nel.org>,
	Mahanta Jambigi <mjambigi@...ux.ibm.com>,
	Tony Lu <tonylu@...ux.alibaba.com>,
	Wen Gu <guwen@...ux.alibaba.com>, Halil Pasic <pasic@...ux.ibm.com>,
	linux-rdma@...r.kernel.org
Subject: Re: [RFC net-next 03/17] net/smc: Remove error handling of
 unregister_dmb()

On 2025-08-06 17:41:08, Alexandra Winter wrote:
>smcd_buf_free() calls smc_ism_unregister_dmb(lgr->smcd, buf_desc) and
>then unconditionally frees buf_desc.
>
>Remove the cleaning up of fields of buf_desc in
>smc_ism_unregister_dmb(), because it is not helpful.
>
>This removes the only usage of ISM_ERROR from the smc module. So move it
>to drivers/s390/net/ism.h.
>
>Signed-off-by: Alexandra Winter <wintera@...ux.ibm.com>
>Reviewed-by: Mahanta Jambigi <mjambigi@...ux.ibm.com>
>---
> drivers/s390/net/ism.h |  1 +
> include/net/smc.h      |  2 --
> net/smc/smc_ism.c      | 14 +++++---------
> net/smc/smc_ism.h      |  3 ++-
> 4 files changed, 8 insertions(+), 12 deletions(-)
>
>diff --git a/drivers/s390/net/ism.h b/drivers/s390/net/ism.h
>index 047fa6101555..b5b03db52fce 100644
>--- a/drivers/s390/net/ism.h
>+++ b/drivers/s390/net/ism.h
>@@ -10,6 +10,7 @@
> #include <asm/pci_insn.h>
> 
> #define UTIL_STR_LEN	16
>+#define ISM_ERROR	0xFFFF
> 
> /*
>  * Do not use the first word of the DMB bits to ensure 8 byte aligned access.
>diff --git a/include/net/smc.h b/include/net/smc.h
>index db84e4e35080..a9c023dd1380 100644
>--- a/include/net/smc.h
>+++ b/include/net/smc.h
>@@ -44,8 +44,6 @@ struct smcd_dmb {
> 
> #define ISM_RESERVED_VLANID	0x1FFF
> 
>-#define ISM_ERROR	0xFFFF
>-
> struct smcd_dev;
> 
> struct smcd_gid {
>diff --git a/net/smc/smc_ism.c b/net/smc/smc_ism.c
>index 84f98e18c7db..a94e1450d095 100644
>--- a/net/smc/smc_ism.c
>+++ b/net/smc/smc_ism.c
>@@ -205,13 +205,13 @@ int smc_ism_put_vlan(struct smcd_dev *smcd, unsigned short vlanid)
> 	return rc;
> }
> 
>-int smc_ism_unregister_dmb(struct smcd_dev *smcd, struct smc_buf_desc *dmb_desc)
>+void smc_ism_unregister_dmb(struct smcd_dev *smcd,
>+			    struct smc_buf_desc *dmb_desc)
> {
> 	struct smcd_dmb dmb;
>-	int rc = 0;
> 
> 	if (!dmb_desc->dma_addr)
>-		return rc;
>+		return;
> 
> 	memset(&dmb, 0, sizeof(dmb));
> 	dmb.dmb_tok = dmb_desc->token;
>@@ -219,13 +219,9 @@ int smc_ism_unregister_dmb(struct smcd_dev *smcd, struct smc_buf_desc *dmb_desc)
> 	dmb.cpu_addr = dmb_desc->cpu_addr;
> 	dmb.dma_addr = dmb_desc->dma_addr;
> 	dmb.dmb_len = dmb_desc->len;
>-	rc = smcd->ops->unregister_dmb(smcd, &dmb);
>-	if (!rc || rc == ISM_ERROR) {
>-		dmb_desc->cpu_addr = NULL;
>-		dmb_desc->dma_addr = 0;
>-	}
>+	smcd->ops->unregister_dmb(smcd, &dmb);

Hmm, I think the old way of handling error here is certainly not good.
But completely ignoring error handling here would make bugs harder
to detect.

What about adding a WARN_ON_ONCE(rc) ?

Also, I think we can just remove the rc == ISM_ERROR to remove
the dependency of ISM_ERROR in smc.

Best regards,
Dust