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On Tue, 25 Mar 2008 01:52:58 -0700, Junio C Hamano wrote: > corbet@lwn.net (Jonathan Corbet) writes: > > > diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h > > index 4982998..63a7782 100644 > > --- a/include/linux/hardirq.h > > +++ b/include/linux/hardirq.h > > @@ -72,6 +72,13 @@ > > #define in_softirq() (softirq_count()) > > #define in_interrupt() (irq_count()) > > > > +/* > > + * Are we running in atomic context? WARNING: this macro cannot > > + * always detect atomic context; in particular, it cannot know about > > + * held spinlocks in non-preemptible kernels. Thus it should not be > > + * used in the general case to determine whether sleeping is possible. > > + * Do not use in_atomic() in driver code. > > + */ > > #define in_atomic() ((preempt_count() & ~PREEMPT_ACTIVE) != 0) > > > > #ifdef CONFIG_PREEMPT > > Is it just me who feels this comment that says "in_atomic() is not a way > to tell if we are in atomic reliably and cannot be used for such and such" > very reader-unfriendly? Ok, maybe the macro is not reliable and is not > meant to be used for the purpose its name seems to suggest (at least to a > non-kernel person). An inevitable question is, then what is it good for? > What's the right situation to use this macro? > > I guess an additional comment "even if this says no, you could still be in > atomic, but if this says yes, then you definitely are in atomic and cannot > sleep" may help unconfuse a clueless reader like myself. Andrew explained that in_atomic() could deadlock if called in a condition where it is unreliable (although I did not understand the details). Documenting that a "yes" from in_atomic() can always be trusted, would invite driver authors to still use it, when my understanding is that they still shouldn't. If drivers shouldn't use in_atomic() at all then I think that the long-term solution is to move its definition out of <linux/hardirq.h>. But of course this means fixing all the drivers that still use it first. -- Jean Delvare -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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