Messages in this thread Patch in this message | | | From | Linus Torvalds <> | Date | Tue, 7 Jun 2011 20:31:02 -0700 | Subject | Re: tty breakage in X (Was: tty vs workqueue oddities) |
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On Tue, Jun 7, 2011 at 7:44 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > Hmm. The n_tty layer has some rather distressing locking, and doesn't > lock "tty->receive_room" changes at all, for example (and uses > multiple locks for some other things). > > It may well be that there is some SMP race there.
Actually, I think it's simpler than that.
Does this patch fix things for you? It just removes the "stop if you've seen the tail, but somebody added a new buffer in the meantime" logic.
We might want to keep the "re-arm the work" for just that case, but let's see what happens if we just remove the logic entirely.
Linus drivers/tty/tty_buffer.c | 14 ++------------ 1 files changed, 2 insertions(+), 12 deletions(-)
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index f1a7918d71aa..6c9b7cd6778a 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -413,8 +413,7 @@ static void flush_to_ldisc(struct work_struct *work) spin_lock_irqsave(&tty->buf.lock, flags); if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) { - struct tty_buffer *head, *tail = tty->buf.tail; - int seen_tail = 0; + struct tty_buffer *head; while ((head = tty->buf.head) != NULL) { int count; char *char_buf; @@ -424,15 +423,6 @@ static void flush_to_ldisc(struct work_struct *work) if (!count) { if (head->next == NULL) break; - /* - There's a possibility tty might get new buffer - added during the unlock window below. We could - end up spinning in here forever hogging the CPU - completely. To avoid this let's have a rest each - time we processed the tail buffer. - */ - if (tail == head) - seen_tail = 1; tty->buf.head = head->next; tty_buffer_free(tty, head); continue; @@ -442,7 +432,7 @@ static void flush_to_ldisc(struct work_struct *work) line discipline as we want to empty the queue */ if (test_bit(TTY_FLUSHPENDING, &tty->flags)) break; - if (!tty->receive_room || seen_tail) + if (!tty->receive_room) break; if (count > tty->receive_room) count = tty->receive_room; | |