We used to include an alignment overhead into a search length, in that
case we guarantee that a found area will definitely fit after applying a
specific alignment that user specifies.  From the other hand we do not
guarantee that an area has the lowest address if an alignment is >=
PAGE_SIZE.

It means that, when a user specifies a special alignment together with a
range that corresponds to an exact requested size then an allocation
will fail.  This is what happens to KASAN, it wants the free block that
exactly matches a specified range during onlining memory banks:

    [root@vm-0 fedora]# echo online > /sys/devices/system/memory/memory82/state
    [root@vm-0 fedora]# echo online > /sys/devices/system/memory/memory83/state
    [root@vm-0 fedora]# echo online > /sys/devices/system/memory/memory85/state
    [root@vm-0 fedora]# echo online > /sys/devices/system/memory/memory84/state
    vmap allocation for size 16777216 failed: use vmalloc=<size> to increase size
    bash: vmalloc: allocation failure: 16777216 bytes, mode:0x6000c0(GFP_KERNEL), nodemask=(null),cpuset=/,mems_allowed=0
    CPU: 4 PID: 1644 Comm: bash Kdump: loaded Not tainted 4.18.0-339.el8.x86_64+debug #1
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
    Call Trace:
     dump_stack+0x8e/0xd0
     warn_alloc.cold.90+0x8a/0x1b2
     ? zone_watermark_ok_safe+0x300/0x300
     ? slab_free_freelist_hook+0x85/0x1a0
     ? __get_vm_area_node+0x240/0x2c0
     ? kfree+0xdd/0x570
     ? kmem_cache_alloc_node_trace+0x157/0x230
     ? notifier_call_chain+0x90/0x160
     __vmalloc_node_range+0x465/0x840
     ? mark_held_locks+0xb7/0x120

Fix it by making sure that find_vmap_lowest_match() returns lowest start
address with any given alignment value, i.e.  for alignments bigger then
PAGE_SIZE the algorithm rolls back toward parent nodes checking right
sub-trees if the most left free block did not fit due to alignment
overhead.

Link: https://lkml.kernel.org/r/20211004142829.22222-1-urezki@gmail.com
Fixes: 68ad4a33 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reported-by: Ping Fang <pifang@redhat.com>
Tested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>