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-resolve.c b/api/src/glfs-resolve.c
index 4b6f76961ee..ebc5282205f 100644
--- a/api/src/glfs-resolve.c
+++ b/api/src/glfs-resolve.c
@@ -65,6 +65,9 @@ __glfs_first_lookup(struct glfs *fs, xlator_t *subvol)
     fs->migration_in_progress = 0;
     pthread_cond_broadcast(&fs->cond);
 
+    /* wake up other waiting tasks */
+    __GLFS_SYNCTASK_WAKE(fs);
+
     return ret;
 }
 
@@ -153,6 +156,9 @@ __glfs_refresh_inode(struct glfs *fs, xlator_t *subvol, inode_t *inode,
     fs->migration_in_progress = 0;
     pthread_cond_broadcast(&fs->cond);
 
+    /* wake up other waiting tasks */
+    __GLFS_SYNCTASK_WAKE(fs);
+
     return newinode;
 }
 
@@ -830,6 +836,9 @@ __glfs_migrate_fd(struct glfs *fs, xlator_t *newsubvol, struct glfs_fd *glfd)
     fs->migration_in_progress = 0;
     pthread_cond_broadcast(&fs->cond);
 
+    /* wake up other waiting tasks */
+    __GLFS_SYNCTASK_WAKE(fs);
+
     return newfd;
 }