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SubjectRe: [PATCH 1/1] mm/cma: fix alloc_contig_range ret code/potential leak
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On 11/20/2017 08:39 PM, Mike Kravetz wrote:
> If the call __alloc_contig_migrate_range() in alloc_contig_range
> returns -EBUSY, processing continues so that test_pages_isolated()
> is called where there is a tracepoint to identify the busy pages.
> However, it is possible for busy pages to become available between
> the calls to these two routines. In this case, the range of pages
> may be allocated. Unfortunately, the original return code (ret
> == -EBUSY) is still set and returned to the caller. Therefore,
> the caller believes the pages were not allocated and they are leaked.
>
> Update the return code with the value from test_pages_isolated().

Good catch and seems ok for a stable fix. But it's another indication
that this area needs some larger rewrite.

For example, it seems that the tracepoints in test_pages_isolated() will
report not only pages which were busy during migration attempt, but also
pages that were not at all attempted, because
__alloc_contig_migrate_range() gave up?

> Fixes: 8ef5849fa8a2 ("mm/cma: always check which page caused allocation failure")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
> 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 77e4d3c5c57b..3605ca82fd29 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7632,10 +7632,10 @@ int alloc_contig_range(unsigned long start, unsigned long end,
> }
>
> /* Make sure the range is really isolated. */
> - if (test_pages_isolated(outer_start, end, false)) {
> + ret = test_pages_isolated(outer_start, end, false);
> + if (ret) {
> pr_info_ratelimited("%s: [%lx, %lx) PFNs busy\n",
> __func__, outer_start, end);
> - ret = -EBUSY;
> goto done;
> }
>
>

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