Commit b48845af authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

bpf: In bpf_task_fd_query use fget_task 

Use the helper fget_task to simplify bpf_task_fd_query.

As well as simplifying the code this removes one unnecessary increment of
struct files_struct.  This unnecessary increment of files_struct.count can
result in exec unnecessarily unsharing files_struct and breaking posix
locks, and it can result in fget_light having to fallback to fget reducing
performance.

This simplification comes from the observation that none of the
callers of get_files_struct actually need to call get_files_struct
that was made when discussing[1] exec and posix file locks.

[1] https://lkml.kernel.org/r/20180915160423.GA31461@redhat.com


Suggested-by: default avatarOleg Nesterov <oleg@redhat.com>
v1: https://lkml.kernel.org/r/20200817220425.9389-5-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/20201120231441.29911-5-ebiederm@xmission.com


Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
parent f43c283a

kernel/bpf/syscall.c

+3 −17
Original line number Diff line number Diff line
@@ -3878,7 +3878,6 @@ static int bpf_task_fd_query(const union bpf_attr *attr, 
	pid_t pid = attr->task_fd_query.pid;

	u32 fd = attr->task_fd_query.fd;

	const struct perf_event *event;

	struct files_struct *files;

	struct task_struct *task;

	struct file *file;

	int err;
@@ -3896,23 +3895,11 @@ static int bpf_task_fd_query(const union bpf_attr *attr, 
	if (!task)

		return -ENOENT;



	files = get_files_struct(task);

	put_task_struct(task);

	if (!files)

		return -ENOENT;



	err = 0;

	spin_lock(&files->file_lock);

	file = fcheck_files(files, fd);

	file = fget_task(task, fd);

	put_task_struct(task);

	if (!file)

		err = -EBADF;

	else

		get_file(file);

	spin_unlock(&files->file_lock);

	put_files_struct(files);



	if (err)

		goto out;

		return -EBADF;



	if (file->f_op == &bpf_link_fops) {

		struct bpf_link *link = file->private_data;
@@ -3952,7 +3939,6 @@ static int bpf_task_fd_query(const union bpf_attr *attr, 
	err = -ENOTSUPP;

put_file:

	fput(file);

out:

	return err;

}