Re: [PATCH 1/1] mm/cma: fix alloc_contig_range ret code/potential leak

[Michal Hocko]

On Mon 20-11-17 11:39:30, 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().

I find the description in 0/0 much more easier to grasp so I would
vote for merging it into the changelog. It took me a while to realize
that we are talking about the success path just from staring into the
diff which doesn't have a sufficient scope to tell the whole story.

Btw. I find embeded description in the diffstat area much more easier to
follow for single patches. Having a cover for a single patch sounds more
like a distraction. Just my 2c

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

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  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;
>  	}
>  
> -- 
> 2.13.6
> 

-- 
Michal Hocko
SUSE Labs