vhost: try to shrink pfdset when fdset_add fails

fdset_add increments pfdset->num, but fdset_del doesn't decrement
pfdset->num, so if we call fdset_add then fdset_del in a loop without
calling fdset_shrink, we can easily exceed MAX_FDS with only a few
number of fds used.

So my solution is simply to call fdset_shrink in fdset_add when it
exceeds MAX_FDS.

Because fdset_shrink and fdset_add locks pfdset->fd_mutex we can't
call fdset_shrink inside fdset_add because that would cause a dead
lock, so this patch split fdset_shrink in two, fdset_shrink and
fdset_shrink_nolock.

Fixes: 59317cef249c ("vhost: allow many vhost-user ports")
Cc: stable@dpdk.org
Signed-off-by: Matthias Gatto <matthias.gatto@outscale.com>

diff --git a/lib/librte_vhost/fd_man.c b/lib/librte_vhost/fd_man.c
index 8a075da..c7a4490 100644 (file)
--- a/lib/librte_vhost/fd_man.c
+++ b/lib/librte_vhost/fd_man.c
@@ -65,17 +65,12 @@ fdset_move(struct fdset *pfdset, int dst, int src)
        pfdset->rwfds[dst] = pfdset->rwfds[src];
 }
 
-/*
- * Find deleted fd entries and remove them
- */
 static void
-fdset_shrink(struct fdset *pfdset)
+fdset_shrink_nolock(struct fdset *pfdset)
 {
        int i;
        int last_valid_idx = get_last_valid_idx(pfdset, pfdset->num - 1);
 
-       pthread_mutex_lock(&pfdset->fd_mutex);
-
        for (i = 0; i < last_valid_idx; i++) {
                if (pfdset->fd[i].fd != -1)
                        continue;
@@ -84,7 +79,16 @@ fdset_shrink(struct fdset *pfdset)
                last_valid_idx = get_last_valid_idx(pfdset, last_valid_idx - 1);
        }
        pfdset->num = last_valid_idx + 1;
+}
 
+/*
+ * Find deleted fd entries and remove them
+ */
+static void
+fdset_shrink(struct fdset *pfdset)
+{
+       pthread_mutex_lock(&pfdset->fd_mutex);
+       fdset_shrink_nolock(pfdset);
        pthread_mutex_unlock(&pfdset->fd_mutex);
 }
 
@@ -151,8 +155,12 @@ fdset_add(struct fdset *pfdset, int fd, fd_cb rcb, fd_cb wcb, void *dat)
        pthread_mutex_lock(&pfdset->fd_mutex);
        i = pfdset->num < MAX_FDS ? pfdset->num++ : -1;
        if (i == -1) {
-               pthread_mutex_unlock(&pfdset->fd_mutex);
-               return -2;
+               fdset_shrink_nolock(pfdset);
+               i = pfdset->num < MAX_FDS ? pfdset->num++ : -1;
+               if (i == -1) {
+                       pthread_mutex_unlock(&pfdset->fd_mutex);
+                       return -2;
+               }
        }
 
        fdset_add_fd(pfdset, i, fd, rcb, wcb, dat);