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. One way to fix this in my mind is to record the last pfn in mem_section. This could be done in memory_preset(), since after that we may assume the section is full. Not sure whether you would like it. -- Wei Yang Help you, Help me
