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SubjectRe: 174cc7187e6f ACPICA: Tables: Back port acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux kernel
On Tue, Jan 10, 2017 at 02:27:16AM +0100, Rafael J. Wysocki wrote:
> On Tue, Jan 10, 2017 at 12:52 AM, Borislav Petkov <bp@alien8.de> wrote:
> > On Tue, Jan 10, 2017 at 12:40:39AM +0100, Borislav Petkov wrote:
> >> Lemme run it.
> >
> > Well, it boots but I get:
> >
> > [ 0.291447] ------------[ cut here ]------------
> > [ 0.291702] WARNING: CPU: 0 PID: 1 at kernel/rcu/tree.c:3993 rcu_scheduler_starting+0x5c/0x70
> > [ 0.292107] Modules linked in:
> > [ 0.292277] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.10.0-rc3+ #21
> > [ 0.292540] Hardware name: HP HP EliteBook 745 G3/807E, BIOS N73 Ver. 01.08 01/28/2016
> > [ 0.292893] Call Trace:
> > [ 0.293072] ? dump_stack+0x46/0x63
> > [ 0.293285] ? __warn+0xec/0x110
> > [ 0.293487] ? rcu_scheduler_starting+0x5c/0x70
> > [ 0.293735] ? kernel_init_freeable+0x58/0x19a
> > [ 0.293976] ? rest_init+0x80/0x80
> > [ 0.294153] ? kernel_init+0xa/0x100
> > [ 0.294334] ? ret_from_fork+0x22/0x30
> > [ 0.294525] ---[ end trace 4c0fe009ed4dc740 ]---
> >
> > TBH, I like Rafael's suggestion in the other mail to stick with fixing
> > this in ACPI, especially this is an ACPI problem, not RCU. Well,
> > more or less: RCU could be taught to *not* do schedule_work() if
> > workqueue_init() hasn't happened yet but that's a tangential.
> >
> > So, I'm going to bed. When I wake up, I want to see working fixes!
> >
> > :-)))
>
> Well, if the https://patchwork.kernel.org/patch/9504277/ patch from Lv
> worked, the attached one should work too (please test), but it can be
> justified in a slightly more convincing way.
>
> Namely, the idea is that acpi_os_read/write_memory() should never be
> used before invoking acpi_os_initialize() and since those are the only
> places where the list of memory regions is walked under RCU without
> extra locking, it is safe to skip the RCU synchronization until that
> happens.
>
> Thanks,
> Rafael

Makes sense to me!

It looks like I can make the grace-period-free boot-time window
for CONFIG_PREEMPT=y kernels quite a bit narrower, but it does not
look like something suitable for jamming into 4.10.

Thanx, Paul

> ---
> drivers/acpi/osl.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> Index: linux-pm/drivers/acpi/osl.c
> ===================================================================
> --- linux-pm.orig/drivers/acpi/osl.c
> +++ linux-pm/drivers/acpi/osl.c
> @@ -378,7 +378,9 @@ static void acpi_os_drop_map_ref(struct
> static void acpi_os_map_cleanup(struct acpi_ioremap *map)
> {
> if (!map->refcount) {
> - synchronize_rcu_expedited();
> + if (acpi_os_initialized)
> + synchronize_rcu_expedited();
> +
> acpi_unmap(map->phys, map->virt);
> kfree(map);
> }
> @@ -671,6 +673,8 @@ acpi_os_read_memory(acpi_physical_addres
> bool unmap = false;
> u64 dummy;
>
> + WARN_ON_ONCE(!acpi_os_initialized);
> +
> rcu_read_lock();
> virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
> if (!virt_addr) {
> @@ -716,6 +720,8 @@ acpi_os_write_memory(acpi_physical_addre
> unsigned int size = width / 8;
> bool unmap = false;
>
> + WARN_ON_ONCE(!acpi_os_initialized);
> +
> rcu_read_lock();
> virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
> if (!virt_addr) {

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