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Date: Tue, 25 Aug 2020 11:22:24 +0300 From: Mika Westerberg <mika.westerberg@...ux.intel.com> To: "Rafael J. Wysocki" <rjw@...ysocki.net> Cc: Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Linux ACPI <linux-acpi@...r.kernel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Alan Stern <stern@...land.harvard.edu>, Utkarsh H Patel <utkarsh.h.patel@...el.com>, Pengfei Xu <pengfei.xu@...el.com> Subject: Re: [PATCH v2] PM: sleep: core: Fix the handling of pending runtime resume requests Hi Rafael, On Mon, Aug 24, 2020 at 07:35:31PM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com> > > It has been reported that system-wide suspend may be aborted in the > absence of any wakeup events due to unforseen interactions of it with > the runtume PM framework. > > One failing scenario is when there are multiple devices sharing an > ACPI power resource and runtime-resume needs to be carried out for > one of them during system-wide suspend (for example, because it needs > to be reconfigured before the whole system goes to sleep). In that > case, the runtime-resume of that device involves turning the ACPI > power resource "on" which in turn causes runtime-resume requests > to be queued up for all of the other devices sharing it. Those > requests go to the runtime PM workqueue which is frozen during > system-wide suspend, so they are not actually taken care of until > the resume of the whole system, but the pm_runtime_barrier() > call in __device_suspend() sees them and triggers system wakeup > events for them which then cause the system-wide suspend to be > aborted if wakeup source objects are in active use. > > Of course, the logic that leads to triggering those wakeup events is > questionable in the first place, because clearly there are cases in > which a pending runtime resume request for a device is not connected > to any real wakeup events in any way (like the one above). Moreover, > it is racy, because the device may be resuming already by the time > the pm_runtime_barrier() runs and so if the driver doesn't take care > of signaling the wakeup event as appropriate, it will be lost. > However, if the driver does take care of that, the extra > pm_wakeup_event() call in the core is redundant. > > Accordingly, drop the conditional pm_wakeup_event() call fron > __device_suspend() and make the latter call pm_runtime_barrier() > alone. Also modify the comment next to that call to reflect the new > code and extend it to mention the need to avoid unwanted interactions > between runtime PM and system-wide device suspend callbacks. > > Fixes: 1e2ef05bb8cf8 ("PM: Limit race conditions between runtime PM and system sleep (v2)") > Reported-by: Mika Westerberg <mika.westerberg@...ux.intel.com> I guess the more correct here is Reported-by: Utkarsh H Patel <utkarsh.h.patel@...el.com> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com> I also got confirmation that this fixes the reported issue and did not seem to cause regressions either :) Please add the following tags: Tested-by: Utkarsh H Patel <utkarsh.h.patel@...el.com> Tested-by: Pengfei Xu <pengfei.xu@...el.com> Thanks for fixing this!
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