The zonelist_update_seq retry was limited to CONFIG_MEMORY_HOTREMOVE,
presumably because only hot-remove takes zones out of a zonelist.
However, build_zonerefs_node() rewrites the zonelists in place, so
onlining the first block of a zone shifts the entries that follow it
in every zonelist containing that zone. This can cause a spurious
allocation failure for a __GFP_THISNODE caller.
For a node with only ZONE_NORMAL, onlining its first ZONE_MOVABLE block
rewrites the node's ZONELIST_NOFALLBACK list as:
[NORMAL, NULL] -> [MOVABLE, NULL] -> [MOVABLE, NORMAL, NULL]
A concurrent GFP_KERNEL | __GFP_THISNODE allocation can observe the
intermediate list, skip ZONE_MOVABLE, and find no eligible zone. With
CONFIG_MEMORY_HOTREMOVE=n, check_retry_zonelist() returns 0 and the
allocation fails even though the node has free ZONE_NORMAL memory.
Gate the sequence checks on CONFIG_MEMORY_HOTPLUG, which covers every
configuration that rebuilds zonelists after boot.
Fixes: 3d36424b3b58 ("mm/page_alloc: fix race condition between
build_all_zonelists and page allocation")
Cc: [email protected]
Reviewed-by: Vlastimil Babka (SUSE) <[email protected]>
Signed-off-by: Gregory Price (Meta) <[email protected]>
---
mm/page_alloc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2daf358269ae7..c7125f6693574 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4404,7 +4404,7 @@ static DEFINE_SEQLOCK(zonelist_update_seq);
static unsigned int zonelist_iter_begin(void)
{
- if (IS_ENABLED(CONFIG_MEMORY_HOTREMOVE))
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
return read_seqbegin(&zonelist_update_seq);
return 0;
@@ -4412,7 +4412,7 @@ static unsigned int zonelist_iter_begin(void)
static unsigned int check_retry_zonelist(unsigned int seq)
{
- if (IS_ENABLED(CONFIG_MEMORY_HOTREMOVE))
+ if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
return read_seqretry(&zonelist_update_seq, seq);
return seq;
--
2.53.0-Meta
