Messages in this thread | | | Subject | Re: [PATCH v9 2/3] PCI: Add tango PCIe host bridge support | From | Mason <> | Date | Tue, 4 Jul 2017 15:08:43 +0200 |
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On 04/07/2017 09:09, Peter Zijlstra wrote:
> On Mon, Jul 03, 2017 at 05:30:28PM +0200, Marc Gonzalez wrote: > >> And at the end of smp8759_config_read: >> >> printk("in_atomic_preempt_off = %d\n", in_atomic_preempt_off()); > > That's confused...
That much is certain. I am indeed grasping at straws.
I grepped "scheduling while atomic", found __schedule_bug() in kernel/sched/core.c and saw
if (IS_ENABLED(CONFIG_DEBUG_PREEMPT) && in_atomic_preempt_off()) { pr_err("Preemption disabled at:"); print_ip_sym(preempt_disable_ip); pr_cont("\n"); }
I thought printing the value of in_atomic_preempt_off() in the callback would indicate whether preemption had already been turned off at that point.
It doesn't work like that?
BTW, why didn't print_ip_sym(preempt_disable_ip); say where preemption had been disabled?
>> [ 1.026568] BUG: scheduling while atomic: swapper/0/1/0x00000002 >> [ 1.032625] 5 locks held by swapper/0/1: >> [ 1.036575] #0: (&dev->mutex){......}, at: [<c038c684>] __driver_attach+0x50/0xd0 >> [ 1.044319] #1: (&dev->mutex){......}, at: [<c038c694>] __driver_attach+0x60/0xd0 >> [ 1.052050] #2: (pci_lock){+.+...}, at: [<c03309d8>] pci_bus_read_config_dword+0x44/0x94 > > This is a raw_spinlock_t, that disables preemption
drivers/pci/access.c
/* * This interrupt-safe spinlock protects all accesses to PCI * configuration space. */ DEFINE_RAW_SPINLOCK(pci_lock);
raw_spin_lock_irqsave(&pci_lock, flags); res = bus->ops->read(bus, devfn, pos, len, &data);
IIUC, it's not possible to call stop_machine() while holding a raw spinlock? What about regular spinlocks? IIUC, in RT, regular spinlocks may sleep?
I didn't find "preempt" or "schedul" in the spinlock doc. https://www.kernel.org/doc/Documentation/locking/spinlocks.txt
> Using stop_machine() is per definition doing it wrong ;-)
Here's the high-level view. My HW is borked and muxes config space and mem space. So I need a way to freeze the entire system, make the config space access, and then return the system to normal. (AFAICT, config space accesses are rare, so if I kill performance for these accesses, the system might remain usable.)
Is there a way to do this? Mark suggested stop_machine but it seems using it in my situation is not quite straight-forward.
Regards.
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