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@xxxxxxxxx> 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) { -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
