Messages in this thread | | | Date | Fri, 3 Apr 2009 02:33:02 +0200 | From | Johannes Weiner <> | Subject | Re: mutex_lock_slowpath warning using mxser tty driver (input/output error) |
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On Thu, Apr 02, 2009 at 11:55:08PM +0100, Alan Cox wrote: > On Thu, 02 Apr 2009 22:23:57 +0200 > Jiri Slaby <jirislaby@gmail.com> wrote: > > > On 04/02/2009 08:44 PM, Alan Cox wrote: > > >> It appears to want to lock a mutex in interrupt context, something > > >> that's a definite no-no. > > >> > > >> CCed the folks who might know a thing or two about the driver. > > > > > > Moxa is not a USB driver so the USB trace at the end makes no sense at > > > all. > > > > Yes, unreliable stack entries, but echo_set_canon_col is called from irq > > context and locks mutex. > > Which means that either the driver is calling the ldisc receive handlers > from an IRQ directly (not allowed) or calling the tty_flip_buffer_push > paths and set tty->low_latency > > 2.6.29 is the first kernel that catches this bug with warnings.
It sets tty->low_latency = 1 on ->open(), unconditionally, and does tty_flip_buffer_push() from the interrupt handler.
Both things seem to have been there for a very long time (git-blame says longer than git).
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