On Wed, Mar 03, 2021 at 07:04:33PM +0000, Catalin Marinas wrote: > On Thu, Feb 11, 2021 at 01:35:56PM +0100, David Hildenbrand wrote: > > On 11.02.21 13:10, Anshuman Khandual wrote: > > > On 2/11/21 5:23 PM, Will Deacon wrote: > > > > ... and dropped. These patches appear to be responsible for a boot > > > > regression reported by CKI: > > > > > > Ahh, boot regression ? These patches only change the behaviour > > > for non boot memory only. > > > > > > > https://lore.kernel.org/r/cki.8D1CB60FEC.K6NJMEFQPV@xxxxxxxxxx > > > > > > Will look into the logs and see if there is something pointing to > > > the problem. > > > > It's strange. One thing I can imagine is a mis-detection of early sections. > > However, I don't see that happening: > > > > In sparse_init_nid(), we: > > 1. Initialize the memmap > > 2. Set SECTION_IS_EARLY | SECTION_HAS_MEM_MAP via > > sparse_init_one_section() > > > > Only hotplugged sections (DIMMs, dax/kmem) set SECTION_HAS_MEM_MAP without > > SECTION_IS_EARLY - which is correct, because these are not early. > > > > So once we know that we have valid_section() -- SECTION_HAS_MEM_MAP is set > > -- early_section() should be correct. > > > > Even if someone would be doing a pfn_valid() after > > memblocks_present()->memory_present() but before > > sparse_init_nid(), we should be fine (!valid_section() -> return 0). > > I couldn't figure out how this could fail with Anshuman's patches. > Will's suspicion is that some invalid/null pointer gets dereferenced > before being initialised but the only case I see is somewhere in > pfn_section_valid() (ms->usage) if valid_section() && !early_section(). > > Assuming that we do get a valid_section(ms) && !early_section(ms), is > there a case where ms->usage is not initialised? I guess races with > section_deactivate() are not possible this early. > > Another situation could be that pfn_valid() returns true when no memory > is mapped for that pfn. The case I wondered about was __pfn_to_section() with a bogus pfn, since with patch 2/2 we call that *before* checking that pfn_to_section_nr() is sane. Will
