On Mon, Aug 17, 2020 at 05:04:16PM -0500, Eric W. Biederman wrote: > 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 simplifies proc_fd_link by > removing unnecessary locking, and reference counting. > > [1] https://lkml.kernel.org/r/20180915160423.GA31461@xxxxxxxxxx > Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx> > Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > --- Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx> > fs/proc/fd.c | 14 ++++---------- > 1 file changed, 4 insertions(+), 10 deletions(-) > > diff --git a/fs/proc/fd.c b/fs/proc/fd.c > index 4048a87c51ee..abfdcb21cc79 100644 > --- a/fs/proc/fd.c > +++ b/fs/proc/fd.c > @@ -141,29 +141,23 @@ static const struct dentry_operations tid_fd_dentry_operations = { > > static int proc_fd_link(struct dentry *dentry, struct path *path) > { > - struct files_struct *files = NULL; > struct task_struct *task; > int ret = -ENOENT; > > task = get_proc_task(d_inode(dentry)); > if (task) { > - files = get_files_struct(task); > - put_task_struct(task); > - } > - > - if (files) { > unsigned int fd = proc_fd(d_inode(dentry)); > struct file *fd_file; > > - spin_lock(&files->file_lock); > - fd_file = fcheck_files(files, fd); > + rcu_read_lock(); > + fd_file = fcheck_task(task, fd); > if (fd_file) { > *path = fd_file->f_path; > path_get(&fd_file->f_path); > ret = 0; > } > - spin_unlock(&files->file_lock); > - put_files_struct(files); > + rcu_read_unlock(); > + put_task_struct(task); > } > > return ret; > -- > 2.25.0 >
