percpu: clean up all mappings when pcpu_map_pages() fails

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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Yosry Ahmed <[e-mail]>
Acked-by: Dennis Zhou <[e-mail]>
Cc: Christoph Lameter (Ampere) <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/percpu-vm.c

···
 	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;