[RFC PATCH 4/4] mm/percpu: stop unmapping the CPU that failed to map

[Hao Ge <hao.ge@linux.dev>]

__pcpu_map_pages() clears the PTEs it installed when it fails, so
pcpu_map_pages() only has to tear down the CPUs it mapped before
the failing one.

Signed-off-by: Hao Ge <hao.ge@linux.dev>
---
 mm/percpu-vm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
index 509d8901835c..59d3a336a6bd 100644
--- a/mm/percpu-vm.c
+++ b/mm/percpu-vm.c
@@ -252,10 +252,11 @@ static int pcpu_map_pages(struct pcpu_chunk *chunk, struct page **pages,
 	return 0;
 err:
 	for_each_possible_cpu(tcpu) {
-		__pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start),
-				   page_end - page_start);
+		/* The failing CPU's partial mapping undoes itself */
 		if (tcpu == cpu)
 			break;
+		__pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start),
+				   page_end - page_start);
 	}
 	pcpu_post_unmap_tlb_flush(chunk, page_start, page_end);
 	return err;
-- 
2.25.1