[LibOS] Add missing locks around dentry->inode accesses

Missing locks are added in `do_getdents()` and `libos_syscall_fchdir()`.
Also, this commit adds a missing call to `put_handle()` in error
handling of `libos_syscall_fchdir()`.

Signed-off-by: g2flyer <[email protected]>

libos/include/libos_process.h

@@ -62,6 +62,8 @@ struct libos_process {
     LISTP_TYPE(libos_child_process) zombies;
 
     struct libos_lock children_lock;
+
+    /* If g_dcache_lock is also required, acquire g_dcache_lock first and then fs_lock */
     struct libos_lock fs_lock;
 
     /* Complete command line for the process, as reported by /proc/[pid]/cmdline; currently filled

libos/src/sys/libos_getcwd.c

@@ -82,26 +82,33 @@ long libos_syscall_fchdir(int fd) {
     if (!hdl)
         return -EBADF;
 
+    int ret;
+    lock(&g_dcache_lock);
+
     struct libos_dentry* dent = hdl->dentry;
 
     if (!dent) {
         log_debug("FD=%d has no path in the filesystem", fd);
-        return -ENOTDIR;
+        ret = -ENOTDIR;
+        goto out;
     }
     if (!dent->inode || dent->inode->type != S_IFDIR) {
         char* path = NULL;
         dentry_abs_path(dent, &path, /*size=*/NULL);
         log_debug("%s is not a directory", path);
         free(path);
-        put_handle(hdl);
-        return -ENOTDIR;
+        ret = -ENOTDIR;
+        goto out;
     }
 
     lock(&g_process.fs_lock);
     get_dentry(dent);
     put_dentry(g_process.cwd);
     g_process.cwd = dent;
     unlock(&g_process.fs_lock);
+    ret = 0;
+out:
     put_handle(hdl);
-    return 0;
+    unlock(&g_dcache_lock);
+    return ret;
 }

libos/src/sys/libos_open.c

@@ -373,12 +373,12 @@ static ssize_t do_getdents(int fd, uint8_t* buf, size_t buf_size, bool is_getden
         goto out_no_unlock;
     }
 
+    lock(&g_dcache_lock);
     if (!hdl->dentry->inode) {
         ret = -ENOENT;
-        goto out_no_unlock;
+        goto out_unlock_only_dcache_lock;
     }
 
-    lock(&g_dcache_lock);
     maybe_lock_pos_handle(hdl);
     lock(&hdl->lock);
 
@@ -467,6 +467,7 @@ static ssize_t do_getdents(int fd, uint8_t* buf, size_t buf_size, bool is_getden
 out:
     unlock(&hdl->lock);
     maybe_unlock_pos_handle(hdl);
+out_unlock_only_dcache_lock:
     unlock(&g_dcache_lock);
 out_no_unlock:
     put_handle(hdl);