Re: [PATCH 10/17] proc/fd: In proc_readfd_common use fnext_task

Al Viro
2020-08-18T02:23:08Z

On Mon, Aug 17, 2020 at 05:04:18PM -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 fnext_task simplifies proc_readfd_common, by moving the checking
> for the maximum file descritor into the generic code, and by
> remvoing the need for capturing and releasing a reference on
> files_struct.

Yecchhh... So you keep locking/unlocking the damn thing for each
descriptor?