On Tue, 2013-01-22 at 23:30 +0000, Seiji Aguchi wrote:
> [Issue]
>
> Current erst driver is kicked in panic case.
> On the other hand, a dynamic memory allocation seems to run in it
> with a following code path.
>
> erst_writer -> erst_write -> __erst_write_to_storage -> many of apei_exec_run
> ->
> ctx->ins_table[entry->instruction].run()
>
> which are functions defined in erst_ins_type table i.e:
>
> apei_exec_read_register -> apei_read -> acpi_os_read_memory64 ->
> acpi_os_ioremap -> ioremap_cache
>
> which possibly involve IOMMU allocator.
>
> I may cause a failure of an erst driver if the panic happens in an interrupt
> context.
>
> [Idea]
>
> If we can remove ioremap_cache() from acpi_os_read_memory() as follows,
> It is easy to fix this issue.
> But I'm not sure if it is feasible because I can't see the reason of tying
> acpi_os_ioremap() from a git log...
>
> Any comment?
>
> <snip>
> @@ -918,10 +918,7 @@ acpi_os_read_memory(acpi_physical_address phys_addr, u64
> *value, u32 width)
> virt_addr = acpi_map_vaddr_lookup(phys_addr, size);
> if (!virt_addr) {
> rcu_read_unlock();
> - virt_addr = acpi_os_ioremap(phys_addr, size);
> - if (!virt_addr)
> - return AE_BAD_ADDRESS;
> - unmap = true;
> + return AE_BAD_ADDRESS;
No. We can not do that. Because some users rely on acpi_os_read_memory
to do ioremap for them.
The correct fixing should be pre-map the io-memory that may be accessed
in erst code patch with acpi_map().
Best Regards,
Huang Ying
> }
>
> if (!value)
> <snip>
>
> Seiji
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