On Thu, Mar 04, 2021 at 09:12:31AM +0100, David Hildenbrand wrote: > On 04.03.21 04:31, Anshuman Khandual wrote: > > On 3/4/21 2:54 AM, Will Deacon wrote: > > > 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. > > > > Right, that is problematic. __pfn_to_section() should not be called without > > first validating pfn_to_section_nr(), as it could cause out-of-bound access > > on mem_section buffer. Will fix that order but as there is no test scenario > > which is definitive for this reported regression, how should we ensure that > > it fixes the problem ? > > Oh, right, I missed that in patch #2. (and when comparing to generic > pfn_valid()). > > I thought bisecting pointed at patch #1, that's why I didn't even have > another look at patch #2. Makes sense. I don't think we ever bisected it beyond these two patches, so it could be either of them. Anshuman -- please work with Veronika on this, as she has access to the problematic machine and was really helpful in debugging this last time. Will
