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SubjectRe: TODO: drivers/pcmcia/ds.c: ds_read & ds_write. SMP locks are missing fix
On Thu, Oct 12, 2000 at 11:38:11AM -0400, Yong Chi wrote:
> Hopefully this will do for SMP locks. =)

Holding a spinlock for this long (especially when you might sleep there in two
places (interruptible_sleep_on, put_user)) is basically a bad idea.
spinlocks are designed to be holded only for short time.
Either protect just a small critical section with a spinlock, or use
semaphores.

> --- ds.c.bak Wed Oct 11 13:05:16 2000
> +++ ds.c Thu Oct 12 11:25:20 2000
> @@ -95,6 +95,7 @@
> u_int user_magic;
> int event_head, event_tail;
> event_t event[MAX_EVENTS];
> + spinlock_t lock;
> struct user_info_t *next;
> } user_info_t;
>
> @@ -567,6 +568,7 @@
> user->event_tail = user->event_head = 0;
> user->next = s->user;
> user->user_magic = USER_MAGIC;
> + spin_lock_init(&user->lock);
> s->user = user;
> file->private_data = user;
>
> @@ -616,6 +618,7 @@
> socket_t i = MINOR(file->f_dentry->d_inode->i_rdev);
> socket_info_t *s;
> user_info_t *user;
> + ssize_t retval=4;
>
> DEBUG(2, "ds_read(socket %d)\n", i);
>
> @@ -625,16 +628,23 @@
> return -EINVAL;
> s = &socket_table[i];
> user = file->private_data;
> - if (CHECK_USER(user))
> - return -EIO;
> -
> + spin_lock(&user->lock);
> + if (CHECK_USER(user)) {
> + retval= -EIO;
> + goto read_out;
> + }
> +
> if (queue_empty(user)) {
> interruptible_sleep_on(&s->queue);
> if (signal_pending(current))
> - return -EINTR;
> + retval= -EINTR;
> + goto read_out;
> }
> put_user(get_queued_event(user), (int *)buf);
> - return 4;
> +
> +read_out:
> + spin_unlock(&user->lock);
> + return retval;
> } /* ds_read */
>
> /*====================================================================*/
> @@ -645,6 +655,7 @@
> socket_t i = MINOR(file->f_dentry->d_inode->i_rdev);
> socket_info_t *s;
> user_info_t *user;
> + ssize_t retval=4;
>
> DEBUG(2, "ds_write(socket %d)\n", i);
>
> @@ -656,18 +667,25 @@
> return -EBADF;
> s = &socket_table[i];
> user = file->private_data;
> - if (CHECK_USER(user))
> - return -EIO;
> + spin_lock(&user->lock);
> + if (CHECK_USER(user)) {
> + retval= -EIO;
> + goto write_out;
> + }
>
> if (s->req_pending) {
> s->req_pending--;
> get_user(s->req_result, (int *)buf);
> if ((s->req_result != 0) || (s->req_pending == 0))
> wake_up_interruptible(&s->request);
> - } else
> - return -EIO;
> + } else {
> + retval= -EIO;
> + goto write_out;
> + }
>
> - return 4;
> +write_out:
> + spin_unlock(&user->lock);
> + return retval;
> } /* ds_write */
>
> /*====================================================================*/


Jakub
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