[PATCH RFC 1/4] fs: protect backing files with rcu

[Christian Brauner <brauner@kernel.org>]

Currently backing files are not under any form of rcu protection.
Switching to rcuref requires rcu protection and so does the speculative
vma lookup. Switch them to the same rcu slab as regular files. There
should be no additional magic required as the lifetime of backing files
are always tied to a regular file.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/file_table.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index eed5ffad9997c24e533f88285deb537ddf9429ed..9fc9048145ca023ef8af8769d5f1234a69f10df1 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -40,6 +40,7 @@ static struct files_stat_struct files_stat = {
 
 /* SLAB cache for file structures */
 static struct kmem_cache *filp_cachep __ro_after_init;
+static struct kmem_cache *bfilp_cachep __ro_after_init;
 
 static struct percpu_counter nr_files __cacheline_aligned_in_smp;
 
@@ -68,7 +69,7 @@ static inline void file_free(struct file *f)
 	put_cred(f->f_cred);
 	if (unlikely(f->f_mode & FMODE_BACKING)) {
 		path_put(backing_file_user_path(f));
-		kfree(backing_file(f));
+		kmem_cache_free(bfilp_cachep, backing_file(f));
 	} else {
 		kmem_cache_free(filp_cachep, f);
 	}
@@ -267,13 +268,13 @@ struct file *alloc_empty_backing_file(int flags, const struct cred *cred)
 	struct backing_file *ff;
 	int error;
 
-	ff = kzalloc(sizeof(struct backing_file), GFP_KERNEL);
+	ff = kmem_cache_zalloc(bfilp_cachep, GFP_KERNEL);
 	if (unlikely(!ff))
 		return ERR_PTR(-ENOMEM);
 
 	error = init_file(&ff->file, flags, cred);
 	if (unlikely(error)) {
-		kfree(ff);
+		kmem_cache_free(bfilp_cachep, ff);
 		return ERR_PTR(error);
 	}
 
@@ -529,6 +530,10 @@ void __init files_init(void)
 	filp_cachep = kmem_cache_create("filp", sizeof(struct file), &args,
 				SLAB_HWCACHE_ALIGN | SLAB_PANIC |
 				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
+
+	bfilp_cachep = kmem_cache_create("bfilp", sizeof(struct backing_file),
+				NULL, SLAB_HWCACHE_ALIGN | SLAB_PANIC |
+				SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU);
 	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
 }
 

-- 
2.45.2