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    Subject[PATCH 08/10] staging: erofs: locked before registering for all new workgroups
    Date
    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>
    ---
    drivers/staging/erofs/unzip_vle.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    diff --git a/drivers/staging/erofs/unzip_vle.c b/drivers/staging/erofs/unzip_vle.c
    index 4e5843e8ee35..a1376f3c6065 100644
    --- a/drivers/staging/erofs/unzip_vle.c
    +++ b/drivers/staging/erofs/unzip_vle.c
    @@ -420,18 +420,22 @@ 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 */
    + if (unlikely(!mutex_trylock(&work->lock)))
    + /* for a new workgroup, try_lock *never* fails */
    + DBG_BUGON(1);
    +
    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;
    }

    --
    2.14.4
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