On Wednesday 02 June 2010, Neil Brown wrote: > On Tue, 1 Jun 2010 12:50:01 +0200 (CEST) > Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > > On Tue, 1 Jun 2010, Neil Brown wrote: > > > > > > I think you have acknowledged that there is a race with suspend - thanks. > > > Next step was "can it be closed". > > > You seem to suggest that it can, but you describe it as a "work around" > > > rather than a "bug fix"... > > > > > > Do you agree that the race is a "bug", and therefore it is appropriate to > > > "fix" it assuming an acceptable fix can be found (which I think it can)? > > > > If we can fix it, yes we definitely should do and not work around it. > > > > Thanks, > > > > tglx > > OK. > Here is my suggestion. > > While I think this patch would actually work, and hope the ugly aspects are > reasonably balanced by the simplicity, I present it primarily as a base for > improvement. > The important part is to present how drivers and user-space can co-operate > to avoid losing wake-events. The details of what happens in the kernel are > certainly up for discussion (as is everything else really of course). > > The user-space suspend daemon avoids losing wake-events by using > fcntl(F_OWNER) to ensure it gets a signal whenever any important wake-event > is ready to be read by user-space. This may involve: > - the one daemon processing all wake events > - Both the suspend daemon and the main event handling daemon opening any > given device that delivers wake events (this should work with input > events ... unless grabbing is needed) > - The event handling daemon giving the suspend-daemon's pid as F_OWNER, and > using poll/select to get the events itself. > > When 'mem' is written to /sys/power/state, suspend_prepare waits in an > interruptible wait until any wake-event that might have been initiated before > the suspend was request, has had a chance to be queued for user-space and > trigger kill_fasync. > Currently this wait is a configurable time after the last wake-event was > initiated. This is hackish, but simple and probably adequate. > If more precise timing is needed and achievable, that can be added later. It > would be an entirely internal change and would not affect the API further. > Some of the code developed for suspend-blockers might be a starting point for > this. > > Drivers should call pm_suspend_delay() whenever a wake-event occurs. This > simply records the time so that the suspend process knows if there is in fact > any need to wait at all. > > The delay to wait after the last pm_suspend_delay() is limited to 10 seconds > and can be set by kernel parameter suspend_block_delay=number-of-milliseconds > It defaults to 2 jiffies (which is possibly too short). > > - Would this fix the "bug"?? > - and address the issues that suspend-blockers was created to address? > - or are the requirements on user-space too onerous? In theory wakeup events can also happen after wait_for_blockers() has returned 0 and I guess we should rollback the suspend in such cases. Rafael -- 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
