Hi Peter, On Thu, Aug 30, 2018 at 12:44:02PM +0200, Peter Zijlstra wrote: > On Thu, Aug 30, 2018 at 05:03:19PM +0800, Feng Tang wrote: > > We hit a kernel panic when enabling earlycon for a platform, the > > call trace is: > > > > panic+0xd2/0x220 > > __alloc_bootmem+0x31/0x34 > > spp_getpage+0x60/0x8a > > fill_pte+0x71/0x130 > > __set_pte_vaddr+0x1d/0x50 > > set_pte_vaddr+0x3c/0x60 > > __native_set_fixmap+0x23/0x30 > > native_set_fixmap+0x30/0x40 > > setup_earlycon+0x1e0/0x32f > > param_setup_earlycon+0x13/0x22 > > do_early_param+0x5b/0x90 > > parse_args+0x1f7/0x300 > > parse_early_options+0x24/0x28 > > parse_early_param+0x65/0x73 > > setup_arch+0x31e/0x9f1 > > start_kernel+0x58/0x44e > > > > The root cause is that when CONFIG_NO_BOOTMEM=y, before > > e820__memblock_setup() is called there is no memory for bootmem > > to allocate, > > Which you bloody well asked for by using NO_BOOTMEM=y. > > Going down this route; adding hacks for every little thing that does > want bootmem, completely defeats the purpose. > > If anything, make the earlycon thing depend on NO_BOOTMEM=n. That also > solves your problem. No earlycon, no panic.
In current x86, the NO_BOOTMEM is "y" by default, and almost all the servers/desktops I could access have CONFIG_BOOTMEM=y, while earlycon is important for enabling new platforms, as well as kernel debugging. IMHO, it's better to keep earlycon capability. Also any alloc_bootmem() call in that time window will trigger panic. Thanks, Feng
