On Sun, 19 Jun 2011, Rafael J. Wysocki wrote: > Well, that was kind of difficult to debug, but not impossible. :-) > > The problem here turns out to be related to the SCSI subsystem. > Namely, when the AHCI controller is suspended, it uses the SCSI error > handling mechanism for scheduling the suspend operation (I'm still at a little > loss why that is necessary, but Tejun says it is :-)). This (after several > convoluted operations) causes scsi_error_handler() to be woken up and > it calls scsi_autopm_get_host(shost), which returns error code (-EAGAIN), > because the runtime PM has been disabled at the host level. Oh no. I was afraid something like this was going to happen eventually. It's clear that we don't want runtime PM kicking in while the SCSI error handler is running. That's why I added the scsi_autopm_get_host(). But this also means we will run into trouble if the error handler needs to be used during a power transition. > This happens because scsi_autopm_get_host() uses > pm_runtime_get_sync(&shost->shost_gendev) and returns error code when > shost_gendev.power.disable_depth is nonzero. Maybe get_sync doesn't need to return an error if the runtime status is already ACTIVE. I'm not sure about this; it's just an idea... > So, the problem is either in scsi_autopm_get_host() that should check the > error code returned by pm_runtime_get_sync(), or in rpm_suspend() that should > return 0 if RPM_GET_PUT is set in flags. I'm inclined to say that the > problem should be fixed in rpm_suspend() and hence the appended patch that > works (well, it probably should be split into three separate patches). Maybe it would be good enough if the error handler ended up doing a get_noresume instead of get_sync? Although I could be wrong, I don't think scsi_error_handler() will ever run in a situation where the host adapter is not runtime-active. Tejun, does that sound right to you? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
