On Fri, 21 Mar 2008 02:36:51 +0100 Michael Buesch <mb@xxxxxxxxx> wrote: > On Friday 21 March 2008 02:31:44 Alan Stern wrote: > > On Thu, 20 Mar 2008, Andrew Morton wrote: > > > > > On Thu, 20 Mar 2008 21:36:04 -0300 Henrique de Moraes Holschuh <hmh@xxxxxxxxxx> wrote: > > > > > > > Well, so far so good for LEDs, but what about the other users of in_atomic > > > > that apparently should not be doing it either? > > > > > > Ho hum. Lots of cc's added. > > > > ... > > > > > The usual pattern for most of the above is > > > > > > if (!in_atomic()) > > > do_something_which_might_sleep(); > > > > > > problem is, in_atomic() returns false inside spinlock on non-preptible > > > kernels. So if anyone calls those functions inside spinlock they will > > > incorrectly schedule and another task can then come in and try take the > > > already-held lock. > > > > > > Now, it happens that in_atomic() returns true on non-preemtible kernels > > > when running in interrupt or softirq context. But if the above code really > > > is using in_atomic() to detect am-i-called-from-interrupt and NOT > > > am-i-called-from-inside-spinlock, they should be using in_irq(), > > > in_softirq() or in_interrupt(). > > > > Presumably most of these places are actually trying to detect > > am-i-allowed-to-sleep. Isn't that what in_atomic() is supposed to do? > > No, I think there is no such check in the kernel. Most likely for performance > reasons, as it would require a global flag that is set on each spinlock. Yup. non-preemptible kernels avoid the inc/dec of current_thread_info->preempt_count on spin_lock/spin_unlock > You simply must always _know_, if you are allowed to sleep or not. This is > done by defining an API. The call-context is part of any kernel API. Yup. 99.99% of kernel code manages to do this... -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
