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SubjectRe: [patch 01/27] fs: cleanup files_lock
On Sat, Apr 25, 2009 at 10:42:34AM +0100, Alan Cox wrote:
> On Sat, 25 Apr 2009 11:20:21 +1000
> npiggin@suse.de wrote:
>
> > Lock tty_files with tty_mutex, provide helpers to manipulate the per-sb
> > files list, and unexport the files_lock spinlock.
>
> This looks half like a backward step to me: It swaps clean method calls
> for open coded stuff and it adds more random undocumented uses to
> tty_mutex, which has far too much already.
>
> I don't think
>
> - file_move(filp, &tty->tty_files);
> +
> + mutex_lock(&tty_mutex);
> + file_list_del(filp);
> + list_add(&filp->f_u.fu_list, &tty->tty_files);
> + mutex_unlock(&tty_mutex);
>
> is exactly an improvement, nor is
>
> - file_move(filp, &tty->tty_files);
> - check_tty_count(tty, "tty_open");
> + mutex_lock(&tty_mutex);
> + BUG_ON(list_empty(&filp->f_u.fu_list));
> + file_list_del(filp); /* __dentry_open has put it on the sb list
> */
> + list_add(&filp->f_u.fu_list, &tty->tty_files);
> + __check_tty_count(tty, "tty_open");
> + mutex_unlock(&tty_mutex);
>
> The basic idea looks totally sound but it can use its own lock and there
> should be helpers so this stuff doesn't have to get open coded.

Yes, I agree it was silly to try reusing tty_mutex for this, as you
and Al point out. I've just added a new spinlock for the tty layer
for the moment, which makes it much more like a mechanical search/
replace.



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