mm/cma: fix placement of trace_cma_alloc_start/finish

The current placement of trace_cma_alloc_start/finish misses the fail
cases: !cma || !cma->count || !cma->bitmap.

trace_cma_alloc_finish is also not emitted for the failure case
where bitmap_count > bitmap_maxno.

Fix these missed cases by moving the start event before the failure
checks and moving the finish event to the out label.

Link: https://lkml.kernel.org/r/20240110012234.3793639-1-kaleshsingh@google.com
Fixes: 7bc1aec5 ("mm: cma: add trace events for CMA alloc perf testing")
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Liam Mark <lmark@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/cma.c

@@ -436,6 +436,9 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
 	unsigned long i;
 	struct page *page = NULL;
 	int ret = -ENOMEM;
+	const char *name = cma ? cma->name : NULL;
+
+	trace_cma_alloc_start(name, count, align);
 
 	if (!cma || !cma->count || !cma->bitmap)
 		goto out;
@@ -446,8 +449,6 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
 	if (!count)
 		goto out;
 
-	trace_cma_alloc_start(cma->name, count, align);
-
 	mask = cma_bitmap_aligned_mask(cma, align);
 	offset = cma_bitmap_aligned_offset(cma, align);
 	bitmap_maxno = cma_bitmap_maxno(cma);
@@ -496,8 +497,6 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
 		start = bitmap_no + mask + 1;
 	}
 
-	trace_cma_alloc_finish(cma->name, pfn, page, count, align, ret);
-
 	/*
 	 * CMA can allocate multiple page blocks, which results in different
 	 * blocks being marked with different tags. Reset the tags to ignore
@@ -516,6 +515,7 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
 
 	pr_debug("%s(): returned %p\n", __func__, page);
 out:
+	trace_cma_alloc_finish(name, pfn, page, count, align, ret);
 	if (page) {
 		count_vm_event(CMA_ALLOC_SUCCESS);
 		cma_sysfs_account_success_pages(cma, count);