[PATCH 19/26] percpu: clean up all mappings when pcpu_map_pages() fails

[Brendan Jackman]

From: Yosry Ahmed <yosryahmed@xxxxxxxxxx>

In pcpu_map_pages(), if __pcpu_map_pages() fails on a CPU, we call
__pcpu_unmap_pages() to clean up mappings on all CPUs where mappings
were created, but not on the CPU where __pcpu_map_pages() fails.

__pcpu_map_pages() and __pcpu_unmap_pages() are wrappers around
vmap_pages_range_noflush() and vunmap_range_noflush(). All other callers
of vmap_pages_range_noflush() call vunmap_range_noflush() when mapping
fails, except pcpu_map_pages(). The reason could be that partial
mappings may be left behind from a failed mapping attempt.

Call __pcpu_unmap_pages() for the failed CPU as well in
pcpu_map_pages().

This was found by code inspection, no failures or bugs were observed.

Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Acked-by: Dennis Zhou <dennis@xxxxxxxxxx>

(am from https://lore.kernel.org/lkml/20240311194346.2291333-1-yosryahmed@xxxxxxxxxx/)
---
 mm/percpu-vm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
index 2054c9213c43..cd69caf6aa8d 100644
--- a/mm/percpu-vm.c
+++ b/mm/percpu-vm.c
@@ -231,10 +231,10 @@ static int pcpu_map_pages(struct pcpu_chunk *chunk,
 	return 0;
 err:
 	for_each_possible_cpu(tcpu) {
-		if (tcpu == cpu)
-			break;
 		__pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start),
 				   page_end - page_start);
+		if (tcpu == cpu)
+			break;
 	}
 	pcpu_post_unmap_tlb_flush(chunk, page_start, page_end);
 	return err;

-- 
2.45.2.993.g49e7a77208-goog