[dpdk-dev] [PATCH v3 1/1] ring: enforce reading the tail before reading ring slots

[Nipun Gupta]

> -----Original Message-----
> From: Gavin Hu [mailto:gavin.hu at arm.com]
> Sent: Tuesday, March 12, 2019 10:29 PM
> To: dev at dpdk.org
> Cc: nd at arm.com; gavin hu <gavin.hu at arm.com>; thomas at monjalon.net;
> konstantin.ananyev at intel.com; jerinj at marvell.com; Hemant Agrawal
> <hemant.agrawal at nxp.com>; Nipun Gupta <nipun.gupta at nxp.com>;
> Honnappa.Nagarahalli at arm.com; i.maximets at samsung.com;
> chaozhu at linux.vnet.ibm.com; stable at dpdk.org
> Subject: [PATCH v3 1/1] ring: enforce reading the tail before reading ring slots
> 
> From: gavin hu <gavin.hu at arm.com>
> 
> In weak memory models, like arm64, reading the prod.tail may get
> reordered after reading the ring slots, which corrupts the ring and
> stale data is observed.
> 
> This issue was reported by NXP on 8-A72 DPAA2 board. The problem is most
> likely caused by missing the acquire semantics when reading
> prod.tail (in SC dequeue) which makes it possible to read a
> stale value from the ring slots.
> 
> For MP (and MC) case, rte_atomic32_cmpset() already provides the required
> ordering. For SP case, the control depependency between if-
> statement(which
> depends on the read of r->cons.tail) and the later stores to the ring slots
> make RMB unnecessary. About the control dependency, read more at:
> https://emea01.safelinks.protection.outlook.com/?url=https:%2F%2Fwww.c
> l.cam.ac.uk%2F~pes20%2Fppc-
> supplemental%2Ftest7.pdf&data=02%7C01%7Cnipun.gupta%40nxp.co
> m%7Cc3df030ec49449bbaf0508d6a70c0b9f%7C686ea1d3bc2b4c6fa92cd99c5c
> 301635%7C0%7C0%7C636880067514602937&sdata=ogPdd%2F4UGYWE8
> nAwY1lkXPCB9MpUIFY0VOQr2N1lwe4%3D&reserved=0
> 
> This patch is adding the required read barrier to prevent reading the ring
> slots get reordered before reading prod.tail for SC case.
> 
> Fixes: c9fb3c62896f ("ring: move code in a new header file")
> Cc: stable at dpdk.org
> 
> Signed-off-by: gavin hu <gavin.hu at arm.com>
> Reviewed-by: Ola Liljedahl <Ola.Liljedahl at arm.com>
> Tested-by: Nipun Gupta <nipun.gupta at nxp.com>

Acked-by: Nipun Gupta <nipun.gupta at nxp.com>

Also, I have revalidated this updated patch.