On 11.12.2018 10:49, Wei Yang wrote: > On Mon, Dec 10, 2018 at 02:24:51PM +0100, Michal Hocko wrote: >> On Mon 10-12-18 14:07:12, Mikhail Zaslonko wrote: >>> If memory end is not aligned with the sparse memory section boundary, the >>> mapping of such a section is only partly initialized. >> >> It would be great to mention how you can end up in the situation like >> this(a user provided memmap or a strange HW). >> >>> This may lead to >>> VM_BUG_ON due to uninitialized struct page access from >>> is_mem_section_removable() or test_pages_in_a_zone() function triggered by >>> memory_hotplug sysfs handlers: >>> >>> page:000003d082008000 is uninitialized and poisoned >>> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) >>> Call Trace: >>> ([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160) >>> [<00000000008f15c4>] show_valid_zones+0x5c/0x190 >>> [<00000000008cf9c4>] dev_attr_show+0x34/0x70 >>> [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148 >>> [<00000000003e4194>] seq_read+0x204/0x480 >>> [<00000000003b53ea>] __vfs_read+0x32/0x178 >>> [<00000000003b55b2>] vfs_read+0x82/0x138 >>> [<00000000003b5be2>] ksys_read+0x5a/0xb0 >>> [<0000000000b86ba0>] system_call+0xdc/0x2d8 >>> Last Breaking-Event-Address: >>> [<0000000000385b26>] test_pages_in_a_zone+0xde/0x160 >>> Kernel panic - not syncing: Fatal exception: panic_on_oops >>> >>> Fix the problem by initializing the last memory section of the highest zone >>> in memmap_init_zone() till the very end, even if it goes beyond the zone >>> end. >> >> Why do we need to restrict this to the highest zone? In other words, why >> cannot we do what I was suggesting earlier [1]. What does prevent other >> zones to have an incomplete section boundary? >> >> [1] http://lkml.kernel.org/r/20181105183533.GQ4361@xxxxxxxxxxxxxx >> > > I tried to go through the original list and make myself familiar with > the bug. > > Confused why initialize the *last* end_pfn could fix this, since > is_mem_section_removable() will iterate on each page of a section. This > means we need to initialize all the pages left in the section. That's exactly what the fix does. We initialize all the pages left in the section. > > One way to fix this in my mind is to record the last pfn in mem_section. Do you mean last initialized pfn? I guess we have agreed upon that the entire section should be initialized. > This could be done in memory_preset(), since after that we may assume > the section is full. Not sure whether you would like it. >
