On Sun, 26 Jun 2011, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rjw@xxxxxxx> > > One of the roles of the PM core is to prevent different PM callbacks > executed for the same device object from racing with each other. > Unfortunately, after commit e8665002477f0278f84f898145b1f141ba26ee26 > (PM: Allow pm_runtime_suspend() to succeed during system suspend) > runtime PM callbacks may be executed concurrently with system > suspend/resume callbacks for the same device. ... > Index: linux-2.6/Documentation/power/runtime_pm.txt > =================================================================== > --- linux-2.6.orig/Documentation/power/runtime_pm.txt > +++ linux-2.6/Documentation/power/runtime_pm.txt > +The PM core does its best to reduce the probability of race conditions between > +the runtime PM and system suspend/resume (and hibernation) callbacks by carrying > +out the following operations: > + > + * During system suspend it acquires a runtime PM reference to every device > + and resume it if there's a runtime PM resume request pending right before > + executing the subsystem-level .suspend() callback for it. In addition to > + that it disables the runtime PM framework for every device right after > + executing the subsystem-level .suspend() callback for it. > + > + * During system resume it enables the runtime PM framework for all devices > + right before executing the subsystem-level .resume() callbacks for them. > + Additionally, it drops references to all devices right after executing the > + subsystem-level .resume() callbacks for them. I think it would be better to be a little more specific here. Instead of "acquires a runtime PM reference", say "calls pm_runtime_get_noresume()". Or at least, say "increments the run-time usage counter". Likewise, instead of "disables the runtime PM framework", say "calls pm_runtime_disable()" or at least "increments power.disable_depth". Hmmm, come to think of it... The documentation for pm_runtime_enable() and pm_runtime_disable() fails to mention power.disable_depth, which is a surprising omission. In particular, the description of pm_runtime_enable() is wrong because it ignores the possibility of nested disables. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
