Date: Mon, 12 May 2014 13:05:04 +0000 (UTC) From: Ian Lepore <ian@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r265913 - head/sys/arm/arm Message-ID: <201405121305.s4CD54GW026630@svn.freebsd.org>
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Author: ian Date: Mon May 12 13:05:03 2014 New Revision: 265913 URL: http://svnweb.freebsd.org/changeset/base/265913 Log: Interrupts need to be disabled on entry to cpu_sleep() for ARM. Given that and the need to be in a critical section when switching to idleclock mode for event timers, use spinlock_enter()/exit() to achieve both needs. The ARM WFI (wait for interrupt) instruction blocks until an interrupt is asserted, and it will unblock even if interrupts are masked, and it will unblock immediately if an interrupt is already pending. It is necessary to execute it with interrupts disabled, otherwise the interrupt that should unblock it may occur and be serviced just prior to executing the instruction. At that point the system is inappropriately asleep until the next timer tick or some other random interrupt happens. In general, interrupts need to be disabled continuously from the time the decision is made that there is no work to be done and sleeping is needed until actually going to sleep, to avoid a race where handling a new interrupt changes the basis for deciding there is no work to be done. Submitted by: hps@ (in slightly different form) Modified: head/sys/arm/arm/machdep.c Modified: head/sys/arm/arm/machdep.c ============================================================================== --- head/sys/arm/arm/machdep.c Mon May 12 12:04:44 2014 (r265912) +++ head/sys/arm/arm/machdep.c Mon May 12 13:05:03 2014 (r265913) @@ -426,9 +426,9 @@ cpu_idle(int busy) CTR2(KTR_SPARE2, "cpu_idle(%d) at %d", busy, curcpu); + spinlock_enter(); #ifndef NO_EVENTTIMERS if (!busy) { - critical_enter(); cpu_idleclock(); } #endif @@ -437,9 +437,9 @@ cpu_idle(int busy) #ifndef NO_EVENTTIMERS if (!busy) { cpu_activeclock(); - critical_exit(); } #endif + spinlock_exit(); CTR2(KTR_SPARE2, "cpu_idle(%d) at %d done", busy, curcpu); }
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