Hi Ruifeng,
Typically, we have followed the convention of adding comments whenever
C11 atomic APIs are used. Can you please add comments indicating why acquire or
release semantics are used?
> -----Original Message-----
> From: Ruifeng Wang <ruifeng.w...@arm.com>
> Sent: Friday, October 11, 2019 9:44 PM
> To: david.h...@intel.com
> Cc: dev@dpdk.org; hka...@marvell.com; Gavin Hu (Arm Technology China)
> <gavin...@arm.com>; Honnappa Nagarahalli
> <honnappa.nagaraha...@arm.com>; nd <n...@arm.com>; Ruifeng Wang (Arm
> Technology China) <ruifeng.w...@arm.com>; sta...@dpdk.org
> Subject: [PATCH v2 1/2] lib/distributor: fix deadlock issue for aarch64
>
> Distributor and worker threads rely on data structs in cache line for
> synchronization. The shared data structs were not protected.
> This caused deadlock issue on weaker memory ordering platforms as aarch64.
> Fix this issue by adding memory barriers to ensure synchronization among
> cores.
>
> Bugzilla ID: 342
> Fixes: 775003ad2f96 ("distributor: add new burst-capable library")
> Cc: sta...@dpdk.org
>
> Signed-off-by: Ruifeng Wang <ruifeng.w...@arm.com>
> Reviewed-by: Gavin Hu <gavin...@arm.com>
> ---
> lib/librte_distributor/meson.build | 5 ++
> lib/librte_distributor/rte_distributor.c | 39 ++++++++++------
> lib/librte_distributor/rte_distributor_v20.c | 49 +++++++++++++-------
> 3 files changed, 63 insertions(+), 30 deletions(-)
>
> diff --git a/lib/librte_distributor/meson.build
> b/lib/librte_distributor/meson.build
> index dba7e3b2a..26577dbc1 100644
> --- a/lib/librte_distributor/meson.build
> +++ b/lib/librte_distributor/meson.build
> @@ -9,3 +9,8 @@ else
> endif
> headers = files('rte_distributor.h')
> deps += ['mbuf']
> +
> +# for clang 32-bit compiles we need libatomic for 64-bit atomic ops if
> +cc.get_id() == 'clang' and dpdk_conf.get('RTE_ARCH_64') == false
> + ext_deps += cc.find_library('atomic')
> +endif
> diff --git a/lib/librte_distributor/rte_distributor.c
> b/lib/librte_distributor/rte_distributor.c
> index 21eb1fb0a..b653146d0 100644
> --- a/lib/librte_distributor/rte_distributor.c
> +++ b/lib/librte_distributor/rte_distributor.c
> @@ -50,7 +50,8 @@ rte_distributor_request_pkt_v1705(struct
> rte_distributor *d,
>
> retptr64 = &(buf->retptr64[0]);
> /* Spin while handshake bits are set (scheduler clears it) */
> - while (unlikely(*retptr64 & RTE_DISTRIB_GET_BUF)) {
> + while (unlikely(__atomic_load_n(retptr64, __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_GET_BUF)) {
> rte_pause();
> uint64_t t = rte_rdtsc()+100;
>
> @@ -76,7 +77,8 @@ rte_distributor_request_pkt_v1705(struct
> rte_distributor *d,
> * Finally, set the GET_BUF to signal to distributor that cache
> * line is ready for processing
> */
> - *retptr64 |= RTE_DISTRIB_GET_BUF;
> + __atomic_store_n(retptr64, *retptr64 | RTE_DISTRIB_GET_BUF,
> + __ATOMIC_RELEASE);
> }
> BIND_DEFAULT_SYMBOL(rte_distributor_request_pkt, _v1705, 17.05);
> MAP_STATIC_SYMBOL(void rte_distributor_request_pkt(struct rte_distributor
> *d, @@ -99,7 +101,8 @@ rte_distributor_poll_pkt_v1705(struct
> rte_distributor *d,
> }
>
> /* If bit is set, return */
> - if (buf->bufptr64[0] & RTE_DISTRIB_GET_BUF)
> + if (__atomic_load_n(&(buf->bufptr64[0]), __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_GET_BUF)
> return -1;
>
> /* since bufptr64 is signed, this should be an arithmetic shift */ @@ -
> 115,7 +118,8 @@ rte_distributor_poll_pkt_v1705(struct rte_distributor *d,
> * mbuf pointers, so toggle the bit so scheduler can start working
> * on the next cacheline while we're working.
> */
> - buf->bufptr64[0] |= RTE_DISTRIB_GET_BUF;
> + __atomic_store_n(&(buf->bufptr64[0]),
> + buf->bufptr64[0] | RTE_DISTRIB_GET_BUF,
> __ATOMIC_RELEASE);
>
> return count;
> }
> @@ -174,6 +178,7 @@ rte_distributor_return_pkt_v1705(struct
> rte_distributor *d,
> return -EINVAL;
> }
>
> + __atomic_thread_fence(__ATOMIC_ACQUIRE);
> for (i = 0; i < RTE_DIST_BURST_SIZE; i++)
> /* Switch off the return bit first */
> buf->retptr64[i] &= ~RTE_DISTRIB_RETURN_BUF; @@ -183,7
> +188,8 @@ rte_distributor_return_pkt_v1705(struct rte_distributor *d,
> RTE_DISTRIB_FLAG_BITS) |
> RTE_DISTRIB_RETURN_BUF;
>
> /* set the GET_BUF but even if we got no returns */
> - buf->retptr64[0] |= RTE_DISTRIB_GET_BUF;
> + __atomic_store_n(&(buf->retptr64[0]),
> + buf->retptr64[0] | RTE_DISTRIB_GET_BUF,
> __ATOMIC_RELEASE);
>
> return 0;
> }
> @@ -273,7 +279,8 @@ handle_returns(struct rte_distributor *d, unsigned
> int wkr)
> unsigned int count = 0;
> unsigned int i;
>
> - if (buf->retptr64[0] & RTE_DISTRIB_GET_BUF) {
> + if (__atomic_load_n(&(buf->retptr64[0]), __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_GET_BUF) {
> for (i = 0; i < RTE_DIST_BURST_SIZE; i++) {
> if (buf->retptr64[i] & RTE_DISTRIB_RETURN_BUF) {
> oldbuf = ((uintptr_t)(buf->retptr64[i] >> @@
> -287,7 +294,7 @@ handle_returns(struct rte_distributor *d, unsigned int wkr)
> d->returns.start = ret_start;
> d->returns.count = ret_count;
> /* Clear for the worker to populate with more returns */
> - buf->retptr64[0] = 0;
> + __atomic_store_n(&(buf->retptr64[0]), 0,
> __ATOMIC_RELEASE);
> }
> return count;
> }
> @@ -307,7 +314,8 @@ release(struct rte_distributor *d, unsigned int wkr)
> struct rte_distributor_buffer *buf = &(d->bufs[wkr]);
> unsigned int i;
>
> - while (!(d->bufs[wkr].bufptr64[0] & RTE_DISTRIB_GET_BUF))
> + while (!(__atomic_load_n(&(d->bufs[wkr].bufptr64[0]),
> __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_GET_BUF))
> rte_pause();
>
> handle_returns(d, wkr);
> @@ -328,7 +336,8 @@ release(struct rte_distributor *d, unsigned int wkr)
> d->backlog[wkr].count = 0;
>
> /* Clear the GET bit */
> - buf->bufptr64[0] &= ~RTE_DISTRIB_GET_BUF;
> + __atomic_store_n(&(buf->bufptr64[0]),
> + buf->bufptr64[0] & ~RTE_DISTRIB_GET_BUF,
> __ATOMIC_RELEASE);
> return buf->count;
>
> }
> @@ -355,7 +364,8 @@ rte_distributor_process_v1705(struct rte_distributor
> *d,
> if (unlikely(num_mbufs == 0)) {
> /* Flush out all non-full cache-lines to workers. */
> for (wid = 0 ; wid < d->num_workers; wid++) {
> - if (d->bufs[wid].bufptr64[0] & RTE_DISTRIB_GET_BUF)
> {
> + if (__atomic_load_n(&(d->bufs[wid].bufptr64[0]),
> + __ATOMIC_ACQUIRE) &
> RTE_DISTRIB_GET_BUF) {
> release(d, wid);
> handle_returns(d, wid);
> }
> @@ -367,7 +377,8 @@ rte_distributor_process_v1705(struct rte_distributor
> *d,
> uint16_t matches[RTE_DIST_BURST_SIZE];
> unsigned int pkts;
>
> - if (d->bufs[wkr].bufptr64[0] & RTE_DISTRIB_GET_BUF)
> + if (__atomic_load_n(&(d->bufs[wkr].bufptr64[0]),
> + __ATOMIC_ACQUIRE) & RTE_DISTRIB_GET_BUF)
> d->bufs[wkr].count = 0;
>
> if ((num_mbufs - next_idx) < RTE_DIST_BURST_SIZE) @@ -
> 465,7 +476,8 @@ rte_distributor_process_v1705(struct rte_distributor *d,
>
> /* Flush out all non-full cache-lines to workers. */
> for (wid = 0 ; wid < d->num_workers; wid++)
> - if ((d->bufs[wid].bufptr64[0] & RTE_DISTRIB_GET_BUF))
> + if ((__atomic_load_n(&(d->bufs[wid].bufptr64[0]),
> + __ATOMIC_ACQUIRE) & RTE_DISTRIB_GET_BUF))
> release(d, wid);
>
> return num_mbufs;
> @@ -574,7 +586,8 @@ rte_distributor_clear_returns_v1705(struct
> rte_distributor *d)
>
> /* throw away returns, so workers can exit */
> for (wkr = 0; wkr < d->num_workers; wkr++)
> - d->bufs[wkr].retptr64[0] = 0;
> + __atomic_store_n(&(d->bufs[wkr].retptr64[0]), 0,
> + __ATOMIC_RELEASE);
> }
> BIND_DEFAULT_SYMBOL(rte_distributor_clear_returns, _v1705, 17.05);
> MAP_STATIC_SYMBOL(void rte_distributor_clear_returns(struct
> rte_distributor *d), diff --git a/lib/librte_distributor/rte_distributor_v20.c
> b/lib/librte_distributor/rte_distributor_v20.c
> index cdc0969a8..41411e3c1 100644
> --- a/lib/librte_distributor/rte_distributor_v20.c
> +++ b/lib/librte_distributor/rte_distributor_v20.c
> @@ -34,9 +34,10 @@ rte_distributor_request_pkt_v20(struct
> rte_distributor_v20 *d,
> union rte_distributor_buffer_v20 *buf = &d->bufs[worker_id];
> int64_t req = (((int64_t)(uintptr_t)oldpkt) << RTE_DISTRIB_FLAG_BITS)
> | RTE_DISTRIB_GET_BUF;
> - while (unlikely(buf->bufptr64 & RTE_DISTRIB_FLAGS_MASK))
> + while (unlikely(__atomic_load_n(&(buf->bufptr64),
> __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_FLAGS_MASK))
> rte_pause();
> - buf->bufptr64 = req;
> + __atomic_store_n(&(buf->bufptr64), req, __ATOMIC_RELEASE);
> }
> VERSION_SYMBOL(rte_distributor_request_pkt, _v20, 2.0);
>
> @@ -45,7 +46,8 @@ rte_distributor_poll_pkt_v20(struct rte_distributor_v20
> *d,
> unsigned worker_id)
> {
> union rte_distributor_buffer_v20 *buf = &d->bufs[worker_id];
> - if (buf->bufptr64 & RTE_DISTRIB_GET_BUF)
> + if (__atomic_load_n(&(buf->bufptr64), __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_GET_BUF)
> return NULL;
>
> /* since bufptr64 is signed, this should be an arithmetic shift */ @@ -
> 73,7 +75,7 @@ rte_distributor_return_pkt_v20(struct rte_distributor_v20 *d,
> union rte_distributor_buffer_v20 *buf = &d->bufs[worker_id];
> uint64_t req = (((int64_t)(uintptr_t)oldpkt) <<
> RTE_DISTRIB_FLAG_BITS)
> | RTE_DISTRIB_RETURN_BUF;
> - buf->bufptr64 = req;
> + __atomic_store_n(&(buf->bufptr64), req, __ATOMIC_RELEASE);
> return 0;
> }
> VERSION_SYMBOL(rte_distributor_return_pkt, _v20, 2.0); @@ -117,7 +119,7
> @@ handle_worker_shutdown(struct rte_distributor_v20 *d, unsigned int
> wkr) {
> d->in_flight_tags[wkr] = 0;
> d->in_flight_bitmask &= ~(1UL << wkr);
> - d->bufs[wkr].bufptr64 = 0;
> + __atomic_store_n(&(d->bufs[wkr].bufptr64), 0, __ATOMIC_RELEASE);
> if (unlikely(d->backlog[wkr].count != 0)) {
> /* On return of a packet, we need to move the
> * queued packets for this core elsewhere.
> @@ -165,18 +167,23 @@ process_returns(struct rte_distributor_v20 *d)
> const int64_t data = d->bufs[wkr].bufptr64;
> uintptr_t oldbuf = 0;
>
> - if (data & RTE_DISTRIB_GET_BUF) {
> + if (__atomic_load_n(&data, __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_GET_BUF) {
> flushed++;
> if (d->backlog[wkr].count)
> - d->bufs[wkr].bufptr64 =
> - backlog_pop(&d-
> >backlog[wkr]);
> + __atomic_store_n(&(d->bufs[wkr].bufptr64),
> + backlog_pop(&d->backlog[wkr]),
> + __ATOMIC_RELEASE);
> else {
> - d->bufs[wkr].bufptr64 =
> RTE_DISTRIB_GET_BUF;
> + __atomic_store_n(&(d->bufs[wkr].bufptr64),
> + RTE_DISTRIB_GET_BUF,
> + __ATOMIC_RELEASE);
> d->in_flight_tags[wkr] = 0;
> d->in_flight_bitmask &= ~(1UL << wkr);
> }
> oldbuf = data >> RTE_DISTRIB_FLAG_BITS;
> - } else if (data & RTE_DISTRIB_RETURN_BUF) {
> + } else if (__atomic_load_n(&data, __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_RETURN_BUF) {
> handle_worker_shutdown(d, wkr);
> oldbuf = data >> RTE_DISTRIB_FLAG_BITS;
> }
> @@ -251,21 +258,26 @@ rte_distributor_process_v20(struct
> rte_distributor_v20 *d,
> }
> }
>
> - if ((data & RTE_DISTRIB_GET_BUF) &&
> + if ((__atomic_load_n(&data, __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_GET_BUF) &&
> (d->backlog[wkr].count || next_mb)) {
>
> if (d->backlog[wkr].count)
> - d->bufs[wkr].bufptr64 =
> - backlog_pop(&d-
> >backlog[wkr]);
> + __atomic_store_n(&(d->bufs[wkr].bufptr64),
> + backlog_pop(&d-
> >backlog[wkr]),
> + __ATOMIC_RELEASE);
>
> else {
> - d->bufs[wkr].bufptr64 = next_value;
> + __atomic_store_n(&(d->bufs[wkr].bufptr64),
> + next_value,
> + __ATOMIC_RELEASE);
> d->in_flight_tags[wkr] = new_tag;
> d->in_flight_bitmask |= (1UL << wkr);
> next_mb = NULL;
> }
> oldbuf = data >> RTE_DISTRIB_FLAG_BITS;
> - } else if (data & RTE_DISTRIB_RETURN_BUF) {
> + } else if (__atomic_load_n(&data, __ATOMIC_ACQUIRE)
> + & RTE_DISTRIB_RETURN_BUF) {
> handle_worker_shutdown(d, wkr);
> oldbuf = data >> RTE_DISTRIB_FLAG_BITS;
> }
> @@ -280,13 +292,16 @@ rte_distributor_process_v20(struct
> rte_distributor_v20 *d,
> * if they are ready */
> for (wkr = 0; wkr < d->num_workers; wkr++)
> if (d->backlog[wkr].count &&
> - (d->bufs[wkr].bufptr64 &
> RTE_DISTRIB_GET_BUF)) {
> + (__atomic_load_n(&(d->bufs[wkr].bufptr64),
> + __ATOMIC_ACQUIRE) &
> RTE_DISTRIB_GET_BUF)) {
>
> int64_t oldbuf = d->bufs[wkr].bufptr64 >>
> RTE_DISTRIB_FLAG_BITS;
> store_return(oldbuf, d, &ret_start, &ret_count);
>
> - d->bufs[wkr].bufptr64 = backlog_pop(&d-
> >backlog[wkr]);
> + __atomic_store_n(&(d->bufs[wkr].bufptr64),
> + backlog_pop(&d->backlog[wkr]),
> + __ATOMIC_RELEASE);
> }
>
> d->returns.start = ret_start;
> --
> 2.17.1
