Runtime PM causes oops on next-20151015

[Thierry Reding]

Hi Rafael, Wonhong,

Todays linux-next breaks rather spectacularly for drivers using runtime
PM. The culprit seems to be this commit:

	commit 7d24068e144adc03b805806645d732cf79488717
	Author: Wonhong Kwon <wonhongkwon@xxxxxxxxx>
	Date:   Tue Oct 6 10:10:20 2015 +0900

	    PM / hibernate: Move pm_init/pm_disk_init to late_initcall_sync

	    pm_init is being invoked by core_initcall and hibernate_image_size_init
	    calculates preferred image size (image_size) based on total pages
	    (totalram_pages). This totalram_pages can be modified during various
	    initcall-s phase and this can cause miscalculated image_size.

	    For example, when CMA is being used, init_cma_reserved_pageblock tries
	    to change the totalram_pages and this job is done during core_initcall.
	    In order words, the totalram_pages doesn't take CMA reserved pages into
	    account when image_size is calculated and it can be too small.

	    Move pm_init and pm_disk_init to late_initcall_sync so that it happens
	    after all other initcall-s change the totalram_pages.

	    Reported-by: Sangseok Lee <sangseok.lee@xxxxxxx>
	    Signed-off-by: Wonhong Kwon <wonhong.kwon@xxxxxxx>
	    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

I can't reply to it directly because I don't have it in any of my mail
boxes (it seems to have been sent only to the linux-pm mailing list,
even Google finds only a single match).

Here's an extract of the oops:

	[    1.395928] Unable to handle kernel NULL pointer dereference at virtual address 00000100
	[    1.404013] pgd = ffffffc000e0e000
	[    1.407417] [00000100] *pgd=000000013c007003, *pud=000000013c007003, *pmd=000000013c008003, *pte=0060000050041707
	[    1.417746] Internal error: Oops: 96000005 [#1] PREEMPT SMP
	[    1.423316] Modules linked in:
	[    1.426400] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.3.0-rc5-next-20151015+ #1338
	[    1.434138] Hardware name: NVIDIA Tegra210 P2371 (P2180/P2597) reference board (DT)
	[    1.441789] task: ffffffc0bc0a8000 ti: ffffffc0bc084000 task.ti: ffffffc0bc084000
	[    1.449280] PC is at __queue_work+0x2c/0x240
	[    1.453551] LR is at queue_work_on+0x60/0x78
	...
	[    1.836517] Call trace:
	[    1.838968] [<ffffffc0000b4134>] __queue_work+0x2c/0x240
	[    1.844280] [<ffffffc0000b43a4>] queue_work_on+0x5c/0x78
	[    1.849599] [<ffffffc00052e508>] rpm_idle+0xc0/0x140
	[    1.854565] [<ffffffc00052e5dc>] __pm_runtime_idle+0x54/0x98
	[    1.860229] [<ffffffc00052414c>] driver_probe_device+0x164/0x2f8
	[    1.866236] [<ffffffc000524378>] __driver_attach+0x98/0xa0
	[    1.871724] [<ffffffc00052231c>] bus_for_each_dev+0x5c/0xa0
	[    1.877294] [<ffffffc000523ab4>] driver_attach+0x1c/0x28
	[    1.882608] [<ffffffc0005236e4>] bus_add_driver+0x1cc/0x238
	[    1.888180] [<ffffffc000524b1c>] driver_register+0x5c/0xf8
	[    1.893675] [<ffffffc000431800>] mipi_dsi_driver_register_full+0x50/0x60
	[    1.900374] [<ffffffc000ba1570>] panel_simple_init+0x2c/0x44
	[    1.906035] [<ffffffc000082934>] do_one_initcall+0x8c/0x1a0
	[    1.911612] [<ffffffc000b80aa8>] kernel_init_freeable+0x150/0x1f8
	[    1.917711] [<ffffffc0007f78fc>] kernel_init+0xc/0xe0

Instrumenting the code shows that pm_wq (passed to queue_work in the
rpm_idle() function) is NULL at this point. This matches up with the
change done in the above-mentioned commit, since now pm_wq only gets
initialized at late_initcall time, whereas all built-in drivers will
already be probed at device_initcall time. So I suspect that this is
going to cause crashes on a whole lot of systems (essentially every
system that tries to use runtime PM from a built-in driver).

Given the commit message I suspect that the right fix would be to split
pm_init() into two functions, one that initializes the hibernation image
and another with the PM core initialization. The pm_hibernate_init() is
probably going to work fine as late_initcall (I assume this was tested)
but the rest should probably stay at core_initcall.

I can provide a patch for the latter if everyone agrees that it's the
right thing, but in the meantime, can you please drop the above patch
from your tree to unbreak linux-next for all affected users?

Thanks,
Thierry

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