[patch 093/262] mm/vmalloc: do not adjust the search size for alignment overhead

Andrew Morton
2021-11-05T20:39:34Z

From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Subject: mm/vmalloc: do not adjust the search size for alignment overhead

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
[ 223.858115] vmap allocation for size 16777216 failed: use vmalloc=<size> to increase size
[ 223.859415] bash: vmalloc: allocation failure: 16777216 bytes, mode:0x6000c0(GFP_KERNEL), nodemask=(null),cpuset=/,mems_allowed=0
[ 223.860992] CPU: 4 PID: 1644 Comm: bash Kdump: loaded Not tainted 4.18.0-339.el8.x86_64+debug #1
[ 223.862149] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 223.863580] Call Trace:
[ 223.863946] dump_stack+0x8e/0xd0
[ 223.864420] warn_alloc.cold.90+0x8a/0x1b2
[ 223.864990] ? zone_watermark_ok_safe+0x300/0x300
[ 223.865626] ? slab_free_freelist_hook+0x85/0x1a0
[ 223.866264] ? __get_vm_area_node+0x240/0x2c0
[ 223.866858] ? kfree+0xdd/0x570
[ 223.867309] ? kmem_cache_alloc_node_trace+0x157/0x230
[ 223.868028] ? notifier_call_chain+0x90/0x160
[ 223.868625] __vmalloc_node_range+0x465/0x840
[ 223.869230] ? 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: 68ad4a330433 ("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>
---

mm/vmalloc.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

--- a/mm/vmalloc.c~mm-vmalloc-do-not-adjust-the-search-size-for-alignment-overhead
+++ a/mm/vmalloc.c
@@ -1195,18 +1195,14 @@ find_vmap_lowest_match(unsigned long siz
{
struct vmap_area *va;
struct rb_node *node;
- unsigned long length;

/* Start from the root. */
node = free_vmap_area_root.rb_node;

- /* Adjust the search size for alignment overhead. */
- length = size + align - 1;
-
while (node) {
va = rb_entry(node, struct vmap_area, rb_node);

- if (get_subtree_max_size(node->rb_left) >= length &&
+ if (get_subtree_max_size(node->rb_left) >= size &&
vstart < va->va_start) {
node = node->rb_left;
} else {
@@ -1216,9 +1212,9 @@ find_vmap_lowest_match(unsigned long siz
/*
* Does not make sense to go deeper towards the right
* sub-tree if it does not have a free block that is
- * equal or bigger to the requested search length.
+ * equal or bigger to the requested search size.
*/
- if (get_subtree_max_size(node->rb_right) >= length) {
+ if (get_subtree_max_size(node->rb_right) >= size) {
node = node->rb_right;
continue;
}
@@ -1226,15 +1222,23 @@ find_vmap_lowest_match(unsigned long siz
/*
* OK. We roll back and find the first right sub-tree,
* that will satisfy the search criteria. It can happen
- * only once due to "vstart" restriction.
+ * due to "vstart" restriction or an alignment overhead
+ * that is bigger then PAGE_SIZE.
*/
while ((node = rb_parent(node))) {
va = rb_entry(node, struct vmap_area, rb_node);
if (is_within_this_va(va, size, align, vstart))
return va;

- if (get_subtree_max_size(node->rb_right) >= length &&
+ if (get_subtree_max_size(node->rb_right) >= size &&
vstart <= va->va_start) {
+ /*
+ * Shift the vstart forward. Please note, we update it with
+ * parent's start address adding "1" because we do not want
+ * to enter same sub-tree after it has already been checked
+ * and no suitable free block found there.
+ */
+ vstart = va->va_start + 1;
node = node->rb_right;
break;
}
_