On Tue, Jul 10, 2018 at 12:06 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: > [+cc Kishon] > > On Mon, Jul 9, 2018 at 4:35 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: >> >> On Mon, Jul 9, 2018 at 3:57 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: >> > On Fri, Jul 6, 2018 at 5:01 AM Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: >> >> >> >> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> >> >> >> >> The devices_kset_move_last() call in really_probe() is a mistake >> >> as it may cause parents to follow children in the devices_kset list >> >> which then causes system shutdown to fail. Namely, if a device has >> >> children before really_probe() is called for it (which is not >> >> uncommon), that call will cause it to be reordered after the children >> >> in the devices_kset list and the ordering of that list will not >> >> reflect the correct device shutdown order. >> >> >> >> Also it causes the devices_kset list to be constantly reordered >> >> until all drivers have been probed which is totally pointless >> >> overhead in the majority of cases. >> >> >> >> For that reason, revert the really_probe() modifications made by >> >> commit 52cdbdd49853. >> > >> > I'm sure you've considered this, but I can't figure out whether this >> > patch will reintroduce the problem that was solved by 52cdbdd49853. >> > That patch updated two places: (1) really_probe(), the change you're >> > reverting here, and (2) device_move(). >> > >> > device_move() is only called from 4-5 places, none of which look >> > related to the problem fixed by 52cdbdd49853, so it seems like that >> > problem was probably resolved by the hunk you're reverting. >> >> That's right, but I don't want to revert all of it. The other parts >> of it are kind of useful as they make the handling of the devices_kset >> list be consistent with the handling of dpm_list. >> >> The hunk I'm reverting, however, is completely off. It not only is >> incorrect (as per the above), but it also causes the devices_kset list >> and dpm_list to be handled differently. > > If I understand correctly, you are saying: > > - the 52cdbdd49853 really_probe() hunk fixed a problem, but It papered over a shutdown failure. Calling it a "fix" is an overstatement IMO. > - that hunk was the wrong fix for it, and > - this patch removes the wrong fix (and probably reintroduces the problem) > > If devices_kset is supposed to be ordered so children follow parents, > I agree the really_probe() hunk doesn't make much sense because the > parent/child relation is determined by the circuit design, not by the > probe order. Exactly. > It just seems like it's worth being clear that we're reintroducing the > problem fixed by 52cdbdd49853, so it needs to be solved a different > way. OK > Ideally that would be done before this patch so there's not a > regression, and this changelog could mention what's happening. Well, commit 52cdbdd49853 introduced a regression by itself, but that regression has only been reported recently. I don't really want to go into a discussion on which of the two regressions is more painful, but then IMO going back to the state from before commit 52cdbdd49853 is fair enough. Hence the patch. >> It had attempted to fix something, but it failed miserably at that. > > If you're saying that 52cdbdd49853 *tried* to fix a DRA7XX_evm reboot > problem, but in fact, it did not fix that problem, then I guess there > should be no issue with reverting that hunk. Again, it hid the reboot problem by changing the core in a way that led to a shutdown regression elsewhere. Also it looks like the platform(s) having that reboot issue do(es)n't really do system-wide suspend/resume, because that "fix" obviously doesn't help there. >> >> Fixes: 52cdbdd49853 (driver core: correct device's shutdown order) >> >> Link: https://lore.kernel.org/lkml/CAFgQCTt7VfqM=UyCnvNFxrSw8Z6cUtAi3HUwR4_xPAc03SgHjQ@xxxxxxxxxxxxxx/ >> >> Reported-by: Pingfan Liu <kernelfans@xxxxxxxxx> >> >> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> >> >> --- >> >> drivers/base/dd.c | 8 -------- >> >> 1 file changed, 8 deletions(-) >> >> >> >> Index: linux-pm/drivers/base/dd.c >> >> =================================================================== >> >> --- linux-pm.orig/drivers/base/dd.c >> >> +++ linux-pm/drivers/base/dd.c >> >> @@ -434,14 +434,6 @@ re_probe: >> >> goto probe_failed; >> >> } >> >> >> >> - /* >> >> - * Ensure devices are listed in devices_kset in correct order >> >> - * It's important to move Dev to the end of devices_kset before >> >> - * calling .probe, because it could be recursive and parent Dev >> >> - * should always go first >> >> - */ >> >> - devices_kset_move_last(dev); >> >> - >> >> if (dev->bus->probe) { >> >> ret = dev->bus->probe(dev); >> >> if (ret) >> >>
