Fix multithread issues when operating on a single shared file

When nrfiles=1, numjobs>1 and create_serialize=0, multiple threads
try to create the single shared file in parallel. If the file was
pre-existing, but an incorrect size, then multiple threads are
deleting and creating at the same time. When all of this happens
in parallel, there is a chance that the file can end up the
incorrect size (the chance increases as numjobs increases).
These changes handle the corner case described above by having
a single thread create/extend the file prior to running all of
the threads in parallel. By doing this step early, when
setup_files() is called later, it should no longer need to
create or extend the file, avoiding the race condition. The user
still needs to set a fallocate option other than 'none' or the
file will end up 0 bytes in size and the race condition will
still occur. It would be simple to add a ftruncate() to the code
to force this, but that would override the user's choice of
fallocate options.

Signed-off-by: Chris Weber <weberc@netapp.com>

backend.c

@@ -2314,8 +2314,25 @@ static void run_threads(struct sk_out *sk_out)
 	for_each_td(td, i) {
 		print_status_init(td->thread_number - 1);
 
-		if (!td->o.create_serialize)
+		if (!td->o.create_serialize) {
+			/*
+			 *  When operating on a single rile in parallel,
+			 *  perform single-threaded early setup so that
+			 *  when setup_files() does not run into issues
+			 *  later.
+			*/
+			if (!i && td->o.nr_files==1) {
+				if (setup_shared_file(td)) {
+					exit_value++;
+					if (td->error)
+						log_err("fio: pid=%d, err=%d/%s\n",
+							(int) td->pid, td->error, td->verror);
+					td_set_runstate(td, TD_REAPED);
+					todo--;
+				}
+			}
 			continue;
+		}
 
 		if (fio_verify_load_state(td))
 			goto reap;

file.h

@@ -201,6 +201,7 @@ struct thread_data;
 extern void close_files(struct thread_data *);
 extern void close_and_free_files(struct thread_data *);
 extern uint64_t get_start_offset(struct thread_data *, struct fio_file *);
+extern int __must_check setup_shared_file(struct thread_data *);
 extern int __must_check setup_files(struct thread_data *);
 extern int __must_check file_invalidate_cache(struct thread_data *, struct fio_file *);
 #ifdef __cplusplus

filesetup.c

@@ -143,7 +143,7 @@ static int extend_file(struct thread_data *td, struct fio_file *f)
 	if (unlink_file || new_layout) {
 		int ret;
 
-		dprint(FD_FILE, "layout unlink %s\n", f->file_name);
+		dprint(FD_FILE, "layout %d unlink %d %s\n", new_layout, unlink_file, f->file_name);
 
 		ret = td_io_unlink_file(td, f);
 		if (ret != 0 && ret != ENOENT) {
@@ -198,6 +198,9 @@ static int extend_file(struct thread_data *td, struct fio_file *f)
 		}
 	}
 
+
+	dprint(FD_FILE, "fill file %s, size %llu\n", f->file_name, (unsigned long long) f->real_file_size);
+
 	left = f->real_file_size;
 	bs = td->o.max_bs[DDIR_WRITE];
 	if (bs > left)
@@ -1078,6 +1081,45 @@ static bool create_work_dirs(struct thread_data *td, const char *fname)
 	return true;
 }
 
+int setup_shared_file(struct thread_data *td)
+{
+	struct fio_file *f;
+	uint64_t file_size;
+	int err = 0;
+
+	if (td->o.nr_files > 1) {
+		log_err("fio: shared file setup called for multiple files\n");
+		return -1;
+	}
+
+	get_file_sizes(td);
+
+	f = td->files[0];
+
+	if (f == NULL) {
+		log_err("fio: NULL shared file\n");
+		return -1;
+	}
+
+	file_size = thread_number * td->o.size;
+	dprint(FD_FILE, "shared setup %s real_file_size=%llu, desired=%llu\n", 
+			f->file_name, (unsigned long long)f->real_file_size, (unsigned long long)file_size);
+
+	if (f->real_file_size < file_size) {
+		dprint(FD_FILE, "fio: extending shared file\n");
+		f->real_file_size = file_size;
+		err = extend_file(td, f);
+		if (!err) {
+			err = __file_invalidate_cache(td, f, 0, f->real_file_size);
+		}
+		get_file_sizes(td);
+		dprint(FD_FILE, "shared setup new real_file_size=%llu\n", 
+				(unsigned long long)f->real_file_size);
+	}
+
+	return err;
+}
+
 /*
  * Open the files and setup files sizes, creating files if necessary.
  */
@@ -1092,7 +1134,7 @@ int setup_files(struct thread_data *td)
 	const unsigned long long bs = td_min_bs(td);
 	uint64_t fs = 0;
 
-	dprint(FD_FILE, "setup files\n");
+	dprint(FD_FILE, "setup files (thread_number=%d, subjob_number=%d)\n", td->thread_number, td->subjob_number);
 
 	old_state = td_bump_runstate(td, TD_SETTING_UP);