staging: erofs: locked before registering for all new workgroups

Let's make sure that the one registering a workgroup will also
take the primary work lock at first for two reasons:
  1) There's no need to introduce such a race window (and consequently
     overhead) between registering and locking, other tasks could break
     in by chance, and the race seems unnecessary (no benefit at all);

  2) It's better to take the primary work when a workgroup
     is registered to apply the cache managed policy, for example,
     if some other tasks break in, it could turn into the in-place
     decompression rather than use as the cached decompression.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/erofs/unzip_vle.c b/drivers/staging/erofs/unzip_vle.c
index 4e5843e8ee353260f72103f4446d7d7556db431f..6aa3c989dd4e1ff77b12f3cfd3255207ca4af58e 100644 (file)
--- a/drivers/staging/erofs/unzip_vle.c
+++ b/drivers/staging/erofs/unzip_vle.c
@@ -420,18 +420,23 @@ z_erofs_vle_work_register(const struct z_erofs_vle_work_finder *f,
        work = z_erofs_vle_grab_primary_work(grp);
        work->pageofs = f->pageofs;
 
+       /*
+        * lock all primary followed works before visible to others
+        * and mutex_trylock *never* fails for a new workgroup.
+        */
+       mutex_trylock(&work->lock);
+
        if (gnew) {
                int err = erofs_register_workgroup(f->sb, &grp->obj, 0);
 
                if (err) {
+                       mutex_unlock(&work->lock);
                        kmem_cache_free(z_erofs_workgroup_cachep, grp);
                        return ERR_PTR(-EAGAIN);
                }
        }
 
        *f->owned_head = *f->grp_ret = grp;
-
-       mutex_lock(&work->lock);
        return work;
 }