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://www.cl.cam.ac.uk/~pes20/ppc-supplemental/test7.pdf
This patch is adding the required read barrier to prevent reading the ring
slots get reordered before reading prod.tail for SC case.
Fixes: c9fb3c6289 ("ring: move code in a new header file")
Cc: stable@dpdk.org
Signed-off-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
Tested-by: Nipun Gupta <nipun.gupta@nxp.com>
Acked-by: Nipun Gupta <nipun.gupta@nxp.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
GCC 8.1 warns:
rte_ring.h:350:46:
warning: conversion to 'uint32_t' {aka 'unsigned int'}
from 'int' may change the sign of the result
[-Wsign-conversion]
update_tail(&r->prod, prod_head, prod_next, is_sp, 1);
The visible apis take unsigned int, then call a private
api taking an int, which finally calls an api taking an
unsigned int.
Convert the private api to take unsigned int removing
5 x warning similar to that shown above.
Fixes: 0dfc98c507 ("ring: separate out head index manipulation")
Cc: stable@dpdk.org
Signed-off-by: Andy Green <andy@warmcat.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
There were warnings with GCC 8.1:
In function '__rte_ring_move_prod_head':
rte_ring_generic.h:76:3:
warning: ISO C90 forbids mixed declarations and code
[-Wdeclaration-after-statement]
const uint32_t cons_tail = r->cons.tail;
^~~~~
In function '__rte_ring_move_cons_head':
rte_ring_generic.h:147:3:
warning: ISO C90 forbids mixed declarations and code
[-Wdeclaration-after-statement]
const uint32_t prod_tail = r->prod.tail;
Fixes: 0dfc98c507 ("ring: separate out head index manipulation")
Cc: stable@dpdk.org
Signed-off-by: Andy Green <andy@warmcat.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Move the common part of rte_ring.h into rte_ring_generic.h.
Move the memory barrier part into update_tail().
No functional changes here.
Suggested-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Suggested-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Signed-off-by: Jia He <jia.he@hxt-semitech.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>
