Re: [RFC PATCH] fs: use a sequence counter instead of file_lock in fd_install

Al Viro
2015-04-16T18:09:59Z

On Thu, Apr 16, 2015 at 02:16:31PM +0200, Mateusz Guzik wrote:
> @@ -165,8 +165,10 @@ static int expand_fdtable(struct files_struct *files, int nr)
> cur_fdt = files_fdtable(files);
> if (nr >= cur_fdt->max_fds) {
> /* Continue as planned */
> + write_seqcount_begin(&files->fdt_seqcount);
> copy_fdtable(new_fdt, cur_fdt);
> rcu_assign_pointer(files->fdt, new_fdt);
> + write_seqcount_end(&files->fdt_seqcount);
> if (cur_fdt != &files->fdtab)
> call_rcu(&cur_fdt->rcu, free_fdtable_rcu);

Interesting. AFAICS, your test doesn't step anywhere near that path,
does it? So basically you never hit the retries during that...