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

[Christian Brauner <brauner@kernel.org>]

Port files to rely on file_ref reference to improve scaling and gain
overflow protection.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 drivers/gpu/drm/i915/gt/shmem_utils.c |  2 +-
 drivers/gpu/drm/vmwgfx/ttm_object.c   |  2 +-
 fs/eventpoll.c                        |  2 +-
 fs/file.c                             | 14 +++++++-------
 fs/file_table.c                       |  6 +++---
 include/linux/fs.h                    |  9 +++++----
 6 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/shmem_utils.c b/drivers/gpu/drm/i915/gt/shmem_utils.c
index 1fb6ff77fd899111a0797dac0edd3f2cfa01f42d..bb696b29ee2c992c6b6d0ec5ae538f9ebbb9ed29 100644
--- a/drivers/gpu/drm/i915/gt/shmem_utils.c
+++ b/drivers/gpu/drm/i915/gt/shmem_utils.c
@@ -40,7 +40,7 @@ struct file *shmem_create_from_object(struct drm_i915_gem_object *obj)
 
 	if (i915_gem_object_is_shmem(obj)) {
 		file = obj->base.filp;
-		atomic_long_inc(&file->f_count);
+		get_file(file);
 		return file;
 	}
 
diff --git a/drivers/gpu/drm/vmwgfx/ttm_object.c b/drivers/gpu/drm/vmwgfx/ttm_object.c
index 3353e97687d1d5d0e05bdc8f26ae4b0aae53a997..a17e62867f3b33cd1aafade244d387b43bb66b51 100644
--- a/drivers/gpu/drm/vmwgfx/ttm_object.c
+++ b/drivers/gpu/drm/vmwgfx/ttm_object.c
@@ -471,7 +471,7 @@ void ttm_object_device_release(struct ttm_object_device **p_tdev)
  */
 static bool __must_check get_dma_buf_unless_doomed(struct dma_buf *dmabuf)
 {
-	return atomic_long_inc_not_zero(&dmabuf->file->f_count) != 0L;
+	return file_ref_get(&dmabuf->file->f_ref);
 }
 
 /**
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 1ae4542f0bd88b07e323d0dd75be6c0fe9fff54f..212383cefe6c9fe13a38061c2c81e5b6ff857925 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1002,7 +1002,7 @@ static struct file *epi_fget(const struct epitem *epi)
 	struct file *file;
 
 	file = epi->ffd.file;
-	if (!atomic_long_inc_not_zero(&file->f_count))
+	if (!file_ref_get(&file->f_ref))
 		file = NULL;
 	return file;
 }
diff --git a/fs/file.c b/fs/file.c
index 1b5fc867d8ddff856501ba49d8c751f888810330..f4df09e92b6158ee40a794a4e0462f57acf595cf 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -972,7 +972,7 @@ static struct file *__get_file_rcu(struct file __rcu **f)
 	if (!file)
 		return NULL;
 
-	if (unlikely(!atomic_long_inc_not_zero(&file->f_count)))
+	if (unlikely(!file_ref_get(&file->f_ref)))
 		return ERR_PTR(-EAGAIN);
 
 	file_reloaded = rcu_dereference_raw(*f);
@@ -986,8 +986,8 @@ static struct file *__get_file_rcu(struct file __rcu **f)
 	OPTIMIZER_HIDE_VAR(file_reloaded_cmp);
 
 	/*
-	 * atomic_long_inc_not_zero() above provided a full memory
-	 * barrier when we acquired a reference.
+	 * file_ref_get() above provided a full memory barrier when we
+	 * acquired a reference.
 	 *
 	 * This is paired with the write barrier from assigning to the
 	 * __rcu protected file pointer so that if that pointer still
@@ -1085,11 +1085,11 @@ static inline struct file *__fget_files_rcu(struct files_struct *files,
 		 * We need to confirm it by incrementing the refcount
 		 * and then check the lookup again.
 		 *
-		 * atomic_long_inc_not_zero() gives us a full memory
-		 * barrier. We only really need an 'acquire' one to
-		 * protect the loads below, but we don't have that.
+		 * file_ref_get() gives us a full memory barrier. We
+		 * only really need an 'acquire' one to protect the
+		 * loads below, but we don't have that.
 		 */
-		if (unlikely(!atomic_long_inc_not_zero(&file->f_count)))
+		if (unlikely(!file_ref_get(&file->f_ref)))
 			continue;
 
 		/*
diff --git a/fs/file_table.c b/fs/file_table.c
index 4b23eb7b79dd9d4ec779f4c01ba2e902988895dc..3f5dc4176b21ff82cc9440ed92a0ad962fdb2046 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -178,7 +178,7 @@ static int init_file(struct file *f, int flags, const struct cred *cred)
 	 * fget-rcu pattern users need to be able to handle spurious
 	 * refcount bumps we should reinitialize the reused file first.
 	 */
-	atomic_long_set(&f->f_count, 1);
+	file_ref_init(&f->f_ref, 1);
 	return 0;
 }
 
@@ -483,7 +483,7 @@ static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
 
 void fput(struct file *file)
 {
-	if (atomic_long_dec_and_test(&file->f_count)) {
+	if (file_ref_put(&file->f_ref)) {
 		struct task_struct *task = current;
 
 		if (unlikely(!(file->f_mode & (FMODE_BACKING | FMODE_OPENED)))) {
@@ -516,7 +516,7 @@ void fput(struct file *file)
  */
 void __fput_sync(struct file *file)
 {
-	if (atomic_long_dec_and_test(&file->f_count))
+	if (file_ref_put(&file->f_ref))
 		__fput(file);
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e3c603d01337650d562405500013f5c4cfed8eb6..fece097d41a8fb47a1483e5418f1e7319405bba2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -45,6 +45,7 @@
 #include <linux/slab.h>
 #include <linux/maple_tree.h>
 #include <linux/rw_hint.h>
+#include <linux/file_ref.h>
 
 #include <asm/byteorder.h>
 #include <uapi/linux/fs.h>
@@ -1030,7 +1031,7 @@ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
  * @f_freeptr: Pointer used by SLAB_TYPESAFE_BY_RCU file cache (don't touch.)
  */
 struct file {
-	atomic_long_t			f_count;
+	file_ref_t			f_ref;
 	spinlock_t			f_lock;
 	fmode_t				f_mode;
 	const struct file_operations	*f_op;
@@ -1078,15 +1079,15 @@ struct file_handle {
 
 static inline struct file *get_file(struct file *f)
 {
-	long prior = atomic_long_fetch_inc_relaxed(&f->f_count);
-	WARN_ONCE(!prior, "struct file::f_count incremented from zero; use-after-free condition present!\n");
+	WARN_ONCE(!file_ref_get(&f->f_ref),
+		  "struct file::f_ref incremented from zero; use-after-free condition present!\n");
 	return f;
 }
 
 struct file *get_file_rcu(struct file __rcu **f);
 struct file *get_file_active(struct file **f);
 
-#define file_count(x)	atomic_long_read(&(x)->f_count)
+#define file_count(f)	file_ref_read(&(f)->f_ref)
 
 #define	MAX_NON_LFS	((1UL<<31) - 1)
 

-- 
2.45.2