[PATCH] erofs-utils: mkfs: fix uninitialized z_erofs_mt_ctrl.mutex

z_erofs_mt_ctrl.mutex guards the multi-threaded compression idle
work-item list but is never initialized: z_erofs_mt_global_init()
initializes g_ictx.mutex and g_ictx.cond, not this one.

A zero-filled pthread_mutex_t happens to be a valid initialized mutex
on glibc, so Linux builds are unaffected by accident.  On macOS a
zeroed mutex is invalid: pthread_mutex_lock() fails with EINVAL and,
since the return value is not checked, the idle-list critical sections
in z_erofs_mt_compress() and erofs_mt_write_compressed_file() run with
no mutual exclusion at all.  The torn list can hand the same work item
to two owners, which corrupts the workqueue and crashes mkfs.erofs
non-deterministically (NULL work dequeued in worker_thread(), SIGABRT,
or corrupted output).  --workers=1 does not help since the race is
between the producer and the reaper thread.

Initialize the mutex statically.

Fixes: 830b27bc23342 ("erofs-utils: mkfs: introduce inner-file
multi-threaded compression")
Closes: https://github.com/erofs/erofs-utils/issues/53
Signed-off-by: Isaiah DeRose-Wilson <[email protected]>
---
 lib/compress.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/compress.c b/lib/compress.c
index 48a18b9..9262afa 100644
--- a/lib/compress.c
+++ b/lib/compress.c
@@ -110,7 +110,9 @@ static struct {
  struct erofs_workqueue wq;
  struct erofs_compress_work *idle;
  pthread_mutex_t mutex;
-} z_erofs_mt_ctrl;
+} z_erofs_mt_ctrl = {
+ .mutex = PTHREAD_MUTEX_INITIALIZER,
+};

 struct z_erofs_compress_fslot {
  struct list_head pending;
-- 
2.55.0