ipc: fix locking while sending messages

  Previously, we were putting an exclusive lock to prevent secondary
processes spinning up while we are sending our messages. However,
using exclusive locks had an effect of disallowing multiple
simultaenous unrelated messages/requests being sent, which was
not the intention behind locking.

Fix it to put a shared lock on the directory. That way, we still
prevent secondary process initializations while sending data over
IPC, but allow multiple unrelated transmissions to proceed.

Fixes: 89f1fe7e6d95 ("eal: lock IPC directory on init and send")
Cc: stable@dpdk.org

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
---

Notes:
    This patch is needed for multiprocess hotplug support [1], to avoid cases
    where multiple requests deadlock while in progress.
    
    [1] http://patches.dpdk.org/project/dpdk/list/?series=252

 lib/librte_eal/common/eal_common_proc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
  

> -----Original Message-----
> From: Burakov, Anatoly
> Sent: Wednesday, June 27, 2018 5:44 PM
> To: dev@dpdk.org
> Cc: Zhang, Qi Z <qi.z.zhang@intel.com>; stable@dpdk.org
> Subject: [PATCH] ipc: fix locking while sending messages
> 
> Previously, we were putting an exclusive lock to prevent secondary processes
> spinning up while we are sending our messages. However, using exclusive
> locks had an effect of disallowing multiple simultaenous unrelated
> messages/requests being sent, which was not the intention behind locking.
> 
> Fix it to put a shared lock on the directory. That way, we still prevent
> secondary process initializations while sending data over IPC, but allow
> multiple unrelated transmissions to proceed.
> 
> Fixes: 89f1fe7e6d95 ("eal: lock IPC directory on init and send")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>

Tested-by: Qi Zhang <qi.z.zhang@intel.com>

Thanks for the quick fix!
Qi

> ---
> 
> Notes:
>     This patch is needed for multiprocess hotplug support [1], to avoid cases
>     where multiple requests deadlock while in progress.
> 
>     [1] http://patches.dpdk.org/project/dpdk/list/?series=252
> 
>  lib/librte_eal/common/eal_common_proc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_eal/common/eal_common_proc.c
> b/lib/librte_eal/common/eal_common_proc.c
> index 707d8ab30..f010ef59e 100644
> --- a/lib/librte_eal/common/eal_common_proc.c
> +++ b/lib/librte_eal/common/eal_common_proc.c
> @@ -786,7 +786,7 @@ mp_send(struct rte_mp_msg *msg, const char *peer,
> int type)
> 
>  	dir_fd = dirfd(mp_dir);
>  	/* lock the directory to prevent processes spinning up while we send */
> -	if (flock(dir_fd, LOCK_EX)) {
> +	if (flock(dir_fd, LOCK_SH)) {
>  		RTE_LOG(ERR, EAL, "Unable to lock directory %s\n",
>  			mp_dir_path);
>  		rte_errno = errno;
> @@ -1020,7 +1020,7 @@ rte_mp_request_sync(struct rte_mp_msg *req,
> struct rte_mp_reply *reply,
> 
>  	dir_fd = dirfd(mp_dir);
>  	/* lock the directory to prevent processes spinning up while we send */
> -	if (flock(dir_fd, LOCK_EX)) {
> +	if (flock(dir_fd, LOCK_SH)) {
>  		RTE_LOG(ERR, EAL, "Unable to lock directory %s\n",
>  			mp_dir_path);
>  		closedir(mp_dir);
> @@ -1146,7 +1146,7 @@ rte_mp_request_async(struct rte_mp_msg *req,
> const struct timespec *ts,
>  	dir_fd = dirfd(mp_dir);
> 
>  	/* lock the directory to prevent processes spinning up while we send */
> -	if (flock(dir_fd, LOCK_EX)) {
> +	if (flock(dir_fd, LOCK_SH)) {
>  		RTE_LOG(ERR, EAL, "Unable to lock directory %s\n",
>  			mp_dir_path);
>  		rte_errno = errno;
> --
> 2.17.1
  

27/06/2018 14:25, Zhang, Qi Z:
> From: Burakov, Anatoly
> > 
> > Previously, we were putting an exclusive lock to prevent secondary processes
> > spinning up while we are sending our messages. However, using exclusive
> > locks had an effect of disallowing multiple simultaenous unrelated
> > messages/requests being sent, which was not the intention behind locking.
> > 
> > Fix it to put a shared lock on the directory. That way, we still prevent
> > secondary process initializations while sending data over IPC, but allow
> > multiple unrelated transmissions to proceed.
> > 
> > Fixes: 89f1fe7e6d95 ("eal: lock IPC directory on init and send")
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> 
> Tested-by: Qi Zhang <qi.z.zhang@intel.com>
> 
> Thanks for the quick fix!
> Qi

Applied, thanks