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SubjectRe: [patch 01/27] fs: cleanup files_lock
[Alan Cc'ed due to tty part of it]

On Sat, Apr 25, 2009 at 11:20:21AM +1000, npiggin@suse.de wrote:

> set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
> filp->private_data = tty;
> - 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 there any problem with just shifting mutex_unlock down from several lines
above?


(in do_tty_hangup)
> + mutex_lock(&tty_mutex);
> +
> /* inuse_filps is protected by the single kernel lock */
> lock_kernel();

isn't it too early?

> @@ -553,8 +566,7 @@ static void do_tty_hangup(struct work_st
> }
> spin_unlock(&redirect_lock);
>
> - check_tty_count(tty, "do_tty_hangup");
> - file_list_lock();

i.e. why not here?

> + __check_tty_count(tty, "do_tty_hangup");
> /* This breaks for file handles being sent over AF_UNIX sockets ? */
> list_for_each_entry(filp, &tty->tty_files, f_u.fu_list) {
> if (filp->f_op->write == redirected_tty_write)

> @@ -1467,9 +1479,9 @@ static void release_one_tty(struct kref
> tty_driver_kref_put(driver);
> module_put(driver->owner);
>
> - file_list_lock();
> + mutex_lock(&tty_mutex);
> list_del_init(&tty->tty_files);
> - file_list_unlock();
> + mutex_unlock(&tty_mutex);

Umm... why is it safe from the deadlock POV?

> @@ -1836,8 +1849,12 @@ got_driver:
> return PTR_ERR(tty);
>
> filp->private_data = tty;
> - 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);

a) why not simply shift mutex_unlock from several lines above?
b) that code really looks b0rken - what happens if you block on that
mutex_lock and somebody else comes and sees (at least) inconsistent
tty->count?

====

Could you split that into direct move (one patch) + changes?

> +/**
> + * mark_files_ro - mark all files read-only
> + * @sb: superblock in question
> + *
> + * All files are marked read-only. We don't care about pending
> + * delete files so this should be used in 'force' mode only.
> + */
> +void mark_files_ro(struct super_block *sb)

BTW, I'd rather merge mnt_write_count one first, so reordering of those
would be appreciated; mnt_write_count + move that function + this patch
is the order I'd prefer.


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