[PATCH 07/17] proc/fd: In tid_fd_mode use fcheck_task

Eric W. Biederman
2020-08-17T22:10:18Z

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.

Using fcheck_task instead of get_files_struct clarifies tid_fd_mode by
removing a step.

[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/proc/fd.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 81882a13212d..4048a87c51ee 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -83,18 +83,13 @@ static const struct file_operations proc_fdinfo_file_operations = {

static bool tid_fd_mode(struct task_struct *task, unsigned fd, fmode_t *mode)
{
- struct files_struct *files = get_files_struct(task);
struct file *file;

- if (!files)
- return false;
-
rcu_read_lock();
- file = fcheck_files(files, fd);
+ file = fcheck_task(task, fd);
if (file)
*mode = file->f_mode;
rcu_read_unlock();
- put_files_struct(files);
return !!file;
}

--
2.25.0