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

[Eric Dumazet]

On Tue, 2015-04-21 at 22:12 +0200, Mateusz Guzik wrote:

> in dup_fd:
>        for (i = open_files; i != 0; i--) {
>                 struct file *f = *old_fds++;
>                 if (f) {
>                         get_file(f);
> 

I see no new requirement here. f is either NULL or not.
multi threaded programs never had a guarantee dup_fd() would catch a non
NULL pointer here.


> at least a data dependency barrier, or maybe smp_rmb for peace of mind
> 
> similarly in do_dup2:
>         tofree = fdt->fd[fd];
>         if (!tofree && fd_is_open(fd, fdt))
>                 goto Ebusy;

Same here.


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