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From: tgw_team(腾讯网关团队) <tgw_team@tencent.com>
To: Stephen Hemminger <stephen@networkplumber.org>,
	ZY Qiu <quzeyao@gmail.com>, Thomas Monjalon <thomas@monjalon.net>,
	Ferruh Yigit <ferruh.yigit@intel.com>,
	Andrew Rybchenko <arybchenko@solarflare.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH v2] rte_ethdev: safer memory access by calling Rx callback
Date: Wed, 4 Mar 2020 18:31:20 +0000
Message-ID: <27746e5b4cee4fad9fd9095d9b83268f@tencent.com> (raw)
In-Reply-To: <20200304095638.7c7fed0b@hermes.lan>

Thank you raising your concerns.

I mean, the original wrong code, but using -O3 optimization yielded a correct result.
My patch makes the effects of -O3 and -O0 consistent.

Unlike other signals that require busy wait, this callback pointer only needs to be read once. So I don't think memory barriers and volatile are needed here.
>On Thu,  5 Mar 2020 01:33:49 +0800
>ZY Qiu <quzeyao@gmail.com> wrote:
>> When compiling with -O0,
>> the compiler does not optimize two memory accesses into one.
>> Leads to accessing a null pointer when queue post Rx burst callback
>> removal while traffic is running.
>> See rte_eth_tx_burst function.
>> Signed-off-by: ZY Qiu <tgw_team@tencent.com>
>This is a problem many places in DPDK. You said it was related to -O0
>but that is just what is causing a more generic problem to be exposed.
>Your solution is not sufficient.
>DPDK is sloppy in several places in handling memory ordering issues     
>    https://en.wikipedia.org/wiki/Memory_ordering
>It should have a macro to do RTE_READ_ONCE(). Several drives have this,
>the Linux kernel has it, Liburcu has it.
>The macro RTE_READ_ONCE() can then be used in many places in DPDK.


  reply	other threads:[~2020-03-04 18:31 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-04 14:05 [dpdk-dev] [PATCH] rte_ethdev: fix unsafe memory access by calling RX callback Tencent TGW team
2020-03-04 14:16 ` Andrew Rybchenko
     [not found]   ` <61a6b7d5533643d692c40dc0ab1a2cdc@tencent.com>
2020-03-04 16:26     ` tgw_team(腾讯网关团队)
2020-03-04 16:15 ` Stephen Hemminger
2020-03-04 16:38   ` [dpdk-dev] [PATCH] rte_ethdev: fix unsafe memory access by calling RX callback.(Internet mail) tgw_team(腾讯网关团队)
2020-03-04 17:37     ` Stephen Hemminger
2020-03-04 17:44       ` [dpdk-dev] [PATCH] rte_ethdev: fix unsafe memory access by calling RX callback tgw_team(腾讯网关团队)
2020-03-04 17:33 ` [dpdk-dev] [PATCH v2] rte_ethdev: safer memory access by calling Rx callback ZY Qiu
2020-03-04 17:56   ` Stephen Hemminger
2020-03-04 18:31     ` tgw_team(腾讯网关团队) [this message]
2020-03-05  9:19   ` Bruce Richardson
2020-03-05 11:27     ` Ananyev, Konstantin
2020-03-05 14:23       ` tgw_team(腾讯网关团队)
2020-03-05 14:47       ` Liang, Ma
2020-03-05 15:19         ` Ananyev, Konstantin
2020-03-05 15:42           ` Liang, Ma
2020-03-05 16:47   ` [dpdk-dev] [PATCH v3] rte_ethdev: safer memory access by calling Rx/Tx callback ZY Qiu
2020-03-05 17:23     ` Jerin Jacob
2020-03-11 12:22     ` Ananyev, Konstantin
2020-03-11 12:26       ` Jerin Jacob
2020-10-01 15:14         ` Ferruh Yigit

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