[PATCH 13/17] file: Remove get_files_struct

Eric W. Biederman
2020-08-17T22:13:08Z

When discussing[1] exec and posix file locks it was realized that none
of the callers of get_files_struct fundamentally needed to call
get_files_struct, and that by switching them to helper functions
instead it will both simplify their code and remove unnecessary
increments of files_struct.count. Those unnecessary increments can
result in exec unnecessarily unsharing files_struct which breaking
posix locks, and it can result in fget_light having to fallback to
fget reducing system performance.

Now that get_files_struct has no more users and can not cause the
problems for posix file locking and fget_light remove get_files_struct
so that it does not gain any new users.

[1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/file.c | 13 -------------
include/linux/fdtable.h | 1 -
2 files changed, 14 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 88f9f78869f8..605e756f3c63 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -410,19 +410,6 @@ static struct fdtable *close_files(struct files_struct * files)
return fdt;
}

-struct files_struct *get_files_struct(struct task_struct *task)
-{
- struct files_struct *files;
-
- task_lock(task);
- files = task->files;
- if (files)
- atomic_inc(&files->count);
- task_unlock(task);
-
- return files;
-}
-
void put_files_struct(struct files_struct *files)
{
if (atomic_dec_and_test(&files->count)) {
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index a3a054084f49..8c4bc6aa19c9 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -108,7 +108,6 @@ struct file *fnext_task(struct task_struct *task, unsigned int *fd);

struct task_struct;

-struct files_struct *get_files_struct(struct task_struct *);
void put_files_struct(struct files_struct *fs);
int unshare_files(void);
struct files_struct *dup_fd(struct files_struct *, unsigned, int *) __latent_entropy;
--
2.25.0