On Mon, Aug 17, 2020 at 05:04:20PM -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. > > Instead hold task_lock for the duration that task->files needs to be > stable in seq_show. The task_lock was already taken in > get_files_struct, and so skipping get_files_struct performs less work > overall, and avoids the problems with the files_struct reference > count. > > [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>
