On Tue, 2006-01-24 at 04:48 +0100, Diego Calleja wrote:
> El Mon, 23 Jan 2006 03:42:43 +0100,
> Diego Calleja <[email protected]> escribió:
>
> > Ok - I seem to be able to reproduce it in a unpatched kernel using
> > a lengthy session. I will try your patch and report back.
>
> It doesn't seems to happen today at least, after a lentghty session
> similar to the one which triggered the bug.
I reasonably sure that your problem is lack
of locking for the new tty buffering scheme.
There is a question of how to best fix it
with minimal code change and impact on performance.
Alan:
Look at the attached patches against 2.6.16-rc1
1. I added an active flag for each tty buffer
2. I added locking to anything that manipulates the
buffer lists or sets/clears an active flag
This uses a lock dedicated to the tty buffer lists
instead of using the tty->read_lock to reduce lock
contention.
3. Calls to tty insertion functions set the active
flag for the tail buffer:
tty_buffer_request_room()
tty_insert_flip_string()
tty_insert_flip_string_flags()
tty_prepare_flip_string()
tty_prepare_flip_string_flags()
tty_insert_flip_char()
4. The active flag is cleared when calling
tty_schedule_flip()
con_schedule_flip()
tty_flip_buffer_push()
This lets the tail buffer be 'owned' by the driver
while filling it. flush_to_ldisc stops when an
active buffer is encountered. Calling the scheduling
functions in #4 releases the buffer for use by flush_to_ldisc.
This scheme centralizes the locking so every driver does not
need to be modified, and avoids excessive locking/unlocking
for each inserted character. The lock is grabbed once by
the driver to activate (get ownership of) the tail buffer.
The driver fills the buffer (possibly one char at a time).
When the driver is done, the buffer is marked inactive and
flush_to_ldisc can process it.
I've done some initial testing with success.
Let me know what you think.
--- linux-2.6.16-rc1/drivers/char/tty_io.c 2006-01-24 15:31:45.000000000 -0600
+++ linux-2.6.16-rc1-mg/drivers/char/tty_io.c 2006-01-24 15:33:28.000000000 -0600
@@ -253,6 +253,7 @@ static void tty_buffer_free_all(struct t
static void tty_buffer_init(struct tty_struct *tty)
{
+ spin_lock_init(&tty->buf.lock);
tty->buf.head = NULL;
tty->buf.tail = NULL;
tty->buf.free = NULL;
@@ -266,6 +267,7 @@ static struct tty_buffer *tty_buffer_all
p->used = 0;
p->size = size;
p->next = NULL;
+ p->active = 0;
p->char_buf_ptr = (char *)(p->data);
p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
/* printk("Flip create %p\n", p); */
@@ -312,25 +314,36 @@ static struct tty_buffer *tty_buffer_fin
int tty_buffer_request_room(struct tty_struct *tty, size_t size)
{
- struct tty_buffer *b = tty->buf.tail, *n;
+ struct tty_buffer *b, *n;
int left = 0;
+ unsigned long flags;
+
+ spin_lock_irqsave(&tty->buf.lock, flags);
/* OPTIMISATION: We could keep a per tty "zero" sized buffer to
remove this conditional if its worth it. This would be invisible
to the callers */
- if(b != NULL)
+ if ((b = tty->buf.tail) != NULL)
left = b->size - b->used;
if(left >= size)
- return size;
+ goto done;
+
/* This is the slow path - looking for new buffers to use */
n = tty_buffer_find(tty, size);
- if(n == NULL)
- return left;
+ if(n == NULL) {
+ size = left;
+ goto done;
+ }
if(b != NULL)
b->next = n;
else
tty->buf.head = n;
tty->buf.tail = n;
+
+done:
+ if (tty->buf.tail != NULL)
+ tty->buf.tail->active = 1;
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
return size;
}
@@ -396,10 +409,12 @@ EXPORT_SYMBOL_GPL(tty_insert_flip_string
int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars, size_t size)
{
int space = tty_buffer_request_room(tty, size);
- struct tty_buffer *tb = tty->buf.tail;
- *chars = tb->char_buf_ptr + tb->used;
- memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
- tb->used += space;
+ if (space) {
+ struct tty_buffer *tb = tty->buf.tail;
+ *chars = tb->char_buf_ptr + tb->used;
+ memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
+ tb->used += space;
+ }
return space;
}
@@ -416,10 +431,12 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_strin
int tty_prepare_flip_string_flags(struct tty_struct *tty, unsigned char **chars, char **flags, size_t size)
{
int space = tty_buffer_request_room(tty, size);
- struct tty_buffer *tb = tty->buf.tail;
- *chars = tb->char_buf_ptr + tb->used;
- *flags = tb->flag_buf_ptr + tb->used;
- tb->used += space;
+ if (space) {
+ struct tty_buffer *tb = tty->buf.tail;
+ *chars = tb->char_buf_ptr + tb->used;
+ *flags = tb->flag_buf_ptr + tb->used;
+ tb->used += space;
+ }
return space;
}
@@ -2748,7 +2765,7 @@ static void flush_to_ldisc(void *private
goto out;
}
spin_lock_irqsave(&tty->read_lock, flags);
- while((tbuf = tty->buf.head) != NULL) {
+ while((tbuf = tty->buf.head) != NULL && !tbuf->active) {
tty->buf.head = tbuf->next;
if (tty->buf.head == NULL)
tty->buf.tail = NULL;
@@ -2852,6 +2869,12 @@ EXPORT_SYMBOL(tty_get_baud_rate);
void tty_flip_buffer_push(struct tty_struct *tty)
{
+ unsigned long flags;
+ spin_lock_irqsave(&tty->buf.lock, flags);
+ if (tty->buf.tail != NULL)
+ tty->buf.tail->active = 0;
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
+
if (tty->low_latency)
flush_to_ldisc((void *) tty);
else
--- linux-2.6.16-rc1/include/linux/tty.h 2006-01-17 09:31:30.000000000 -0600
+++ linux-2.6.16-rc1-mg/include/linux/tty.h 2006-01-24 14:12:19.000000000 -0600
@@ -57,6 +57,7 @@ struct tty_buffer {
unsigned char *flag_buf_ptr;
int used;
int size;
+ int active;
/* Data points here */
unsigned long data[0];
};
@@ -64,6 +65,7 @@ struct tty_buffer {
struct tty_bufhead {
struct work_struct work;
struct semaphore pty_sem;
+ spinlock_t lock;
struct tty_buffer *head; /* Queue head */
struct tty_buffer *tail; /* Active buffer */
struct tty_buffer *free; /* Free queue head */
--- linux-2.6.16-rc1/include/linux/tty_flip.h 2006-01-24 12:24:47.000000000 -0600
+++ linux-2.6.16-rc1-mg/include/linux/tty_flip.h 2006-01-24 14:46:59.000000000 -0600
@@ -17,7 +17,7 @@ _INLINE_ int tty_insert_flip_char(struct
unsigned char ch, char flag)
{
struct tty_buffer *tb = tty->buf.tail;
- if (tb && tb->used < tb->size) {
+ if (tb && tb->active && tb->used < tb->size) {
tb->flag_buf_ptr[tb->used] = flag;
tb->char_buf_ptr[tb->used++] = ch;
return 1;
@@ -27,6 +27,11 @@ _INLINE_ int tty_insert_flip_char(struct
_INLINE_ void tty_schedule_flip(struct tty_struct *tty)
{
+ unsigned long flags;
+ spin_lock_irqsave(&tty->buf.lock, flags);
+ if (tty->buf.tail != NULL)
+ tty->buf.tail->active = 0;
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
schedule_delayed_work(&tty->buf.work, 1);
}
--- linux-2.6.16-rc1/include/linux/kbd_kern.h 2006-01-17 09:31:29.000000000 -0600
+++ linux-2.6.16-rc1-mg/include/linux/kbd_kern.h 2006-01-24 15:38:19.000000000 -0600
@@ -151,6 +151,11 @@ extern unsigned int keymap_count;
static inline void con_schedule_flip(struct tty_struct *t)
{
+ unsigned long flags;
+ spin_lock_irqsave(&t->buf.lock, flags);
+ if (t->buf.tail != NULL)
+ t->buf.tail->active = 0;
+ spin_unlock_irqrestore(&t->buf.lock, flags);
schedule_work(&t->buf.work);
}
-
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