Re: [PATCH v2 3/3] fs: port files to file_ref

[Christian Brauner <brauner@xxxxxxxxxx>]

> Actually, thinking about this again, I guess there's actually no
> reason why you'd need a constructor function; if you just avoid
> memset()ing the refcount field on allocation, that'd be good enough.

Thanks for catching this. So what I did is:

diff --git a/fs/file_table.c b/fs/file_table.c
index 5b8b18259eca..c81a47aea47f 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -148,10 +148,14 @@ static int __init init_fs_stat_sysctls(void)
 fs_initcall(init_fs_stat_sysctls);
 #endif

+static_assert(offsetof(struct file, f_ref) == 0);
+
 static int init_file(struct file *f, int flags, const struct cred *cred)
 {
        int error;

+       memset(f + sizeof(file_ref_t), 0, sizeof(*f) - sizeof(file_ref_t));
+
        f->f_cred = get_cred(cred);
        error = security_file_alloc(f);
        if (unlikely(error)) {
@@ -209,7 +213,7 @@ struct file *alloc_empty_file(int flags, const struct cred *cred)
                        goto over;
        }

-       f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
+       f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
        if (unlikely(!f))
                return ERR_PTR(-ENOMEM);

@@ -243,7 +247,7 @@ struct file *alloc_empty_file_noaccount(int flags, const struct cred *cred)
        struct file *f;
        int error;

-       f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
+       f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
        if (unlikely(!f))
                return ERR_PTR(-ENOMEM);

@@ -270,7 +274,7 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
        struct backing_file *ff;
        int error;

-       ff = kmem_cache_zalloc(bfilp_cachep, GFP_KERNEL);
+       ff = kmem_cache_alloc(bfilp_cachep, GFP_KERNEL);
        if (unlikely(!ff))
                return ERR_PTR(-ENOMEM);