gfapi: Suspend synctasks instead of blocking them

There are certain conditions which blocks the current
execution thread (like waiting on mutex lock or condition
variable or I/O response). In such cases, if it is a
synctask thread, we should suspend the task instead
of blocking it (like done in SYNCOP using synctask_yield)

This is to avoid deadlock like the one mentioned below -

1) synctaskA sets fs->migration_in_progress to 1 and
   does I/O (LOOKUP)
2) Other synctask threads wait for fs->migration_in_progress
  to be reset to 0 by synctaskA and hence blocked
3) but synctaskA cannot resume as all synctask threads are blocked
   on (2).

Note: this same approach is already used by few other components
like syncbarrier etc.

Change-Id: If90f870d663bb242c702a5b86ac52eeda67c6f0d
Fixes: #1146
Signed-off-by: Soumya Koduri <skoduri@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/api/src/glfs.c b/api/src/glfs.c
index 5f683451c21..93e0938b815 100644
--- a/api/src/glfs.c
+++ b/api/src/glfs.c
@@ -737,6 +737,7 @@ glfs_new_fs(const char *volname)
 
     INIT_LIST_HEAD(&fs->openfds);
     INIT_LIST_HEAD(&fs->upcall_list);
+    INIT_LIST_HEAD(&fs->waitq);
 
     PTHREAD_MUTEX_INIT(&fs->mutex, NULL, fs->pthread_flags, GLFS_INIT_MUTEX,
                        err);
@@ -1240,6 +1241,7 @@ pub_glfs_fini(struct glfs *fs)
     call_pool_t *call_pool = NULL;
     int fs_init = 0;
     int err = -1;
+    struct synctask *waittask = NULL;
 
     DECLARE_OLD_THIS;
 
@@ -1261,6 +1263,13 @@ pub_glfs_fini(struct glfs *fs)
 
     call_pool = fs->ctx->pool;
 
+    /* Wake up any suspended synctasks */
+    while (!list_empty(&fs->waitq)) {
+        waittask = list_entry(fs->waitq.next, struct synctask, waitq);
+        list_del_init(&waittask->waitq);
+        synctask_wake(waittask);
+    }
+
     while (countdown--) {
         /* give some time for background frames to finish */
         pthread_mutex_lock(&fs->mutex);