Messages in this thread | | | Date | Thu, 30 Aug 2018 14:39:41 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for NO_BOOTMEM |
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On Thu 30-08-18 14:09:26, Peter Zijlstra wrote: > On Thu, Aug 30, 2018 at 01:12:07PM +0200, Michal Hocko wrote: > > On Thu 30-08-18 12:44:02, 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. > > > > Well, there is endeavor to remove bootmem allocator altogether. So > > wasn't aware of that. why?
Because it is yet another allocator that we have to maintain and that is not really needed.
> > making earlycon depend on NO_BOOTMEM=n doesn't sound like a good fit to > > me. I am not familiar with this code path but why cannot we postpone the > > allocation to later or use a statically allocated storage? > > because 'early'... I suppose. Youu really want the early con up and > running asap.
Well, the memblock allocator is initialized quite early as well... If that is not early enough then we have to play tricks. -- Michal Hocko SUSE Labs
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