Re: [dpdk-dev] [PATCH] vhost: fix race condition in fdset_add

[Maxime Coquelin]

Hi Matthias,

On 12/6/18 5:00 PM, Matthias Gatto wrote:

fdset_add can call fdset_shrink_nolock which call fdset_move
concurrently to poll that is call in fdset_event_dispatch.

This patch add a mutex to protect poll from been call at the same time
fdset_add call fdset_shrink_nolock.

Signed-off-by: Matthias Gatto <matthias.ga...@outscale.com>
---
  lib/librte_vhost/fd_man.c | 4 ++++
  lib/librte_vhost/fd_man.h | 1 +
  lib/librte_vhost/socket.c | 1 +
  3 files changed, 6 insertions(+)

diff --git a/lib/librte_vhost/fd_man.c b/lib/librte_vhost/fd_man.c
index 38347ab..55d4856 100644
--- a/lib/librte_vhost/fd_man.c
+++ b/lib/librte_vhost/fd_man.c
@@ -129,7 +129,9 @@
        pthread_mutex_lock(&pfdset->fd_mutex);
        i = pfdset->num < MAX_FDS ? pfdset->num++ : -1;
        if (i == -1) {
+               pthread_mutex_lock(&pfdset->fd_pooling_mutex);
                fdset_shrink_nolock(pfdset);
+               pthread_mutex_unlock(&pfdset->fd_pooling_mutex);
                i = pfdset->num < MAX_FDS ? pfdset->num++ : -1;
                if (i == -1) {
                        pthread_mutex_unlock(&pfdset->fd_mutex);
@@ -246,7 +248,9 @@
                numfds = pfdset->num;
                pthread_mutex_unlock(&pfdset->fd_mutex);

+ pthread_mutex_lock(&pfdset->fd_pooling_mutex);

                val = poll(pfdset->rwfds, numfds, 1000 /* millisecs */);
+               pthread_mutex_unlock(&pfdset->fd_pooling_mutex);

Any reason we cannot use the existing fd_mutex?

                if (val < 0)
                        continue;

diff --git a/lib/librte_vhost/fd_man.h b/lib/librte_vhost/fd_man.h

index 3331bcd..3ab5cfd 100644
--- a/lib/librte_vhost/fd_man.h
+++ b/lib/librte_vhost/fd_man.h
@@ -24,6 +24,7 @@ struct fdset {
        struct pollfd rwfds[MAX_FDS];
        struct fdentry fd[MAX_FDS];
        pthread_mutex_t fd_mutex;
+       pthread_mutex_t fd_pooling_mutex;
        int num;        /* current fd number of this fdset */

union pipefds {

diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index d630317..cc4e748 100644
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -88,6 +88,7 @@ struct vhost_user {
        .fdset = {
                .fd = { [0 ... MAX_FDS - 1] = {-1, NULL, NULL, NULL, 0} },
                .fd_mutex = PTHREAD_MUTEX_INITIALIZER,
+               .fd_pooling_mutex = PTHREAD_MUTEX_INITIALIZER,
                .num = 0
        },
        .vsocket_cnt = 0,