Re: [PATCH] lib/dma-debug.c: fix __hash_bucket_find

From: Shuah Khan
Date: Thu Oct 18 2012 - 13:21:24 EST


On Thu, 2012-10-18 at 23:53 +0800, Ming Lei wrote:
> Hi,
>
> Below v1 should be more efficient and simper, sorry for the noise.
>
>
> Thanks,
> --
> Ming Lei
>
> --
> From d275d195794ff80e018145f2fae714b35ddc49e2 Mon Sep 17 00:00:00 2001
> From: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> Date: Thu, 18 Oct 2012 23:30:57 +0800
> Subject: [PATCH v1] lib/dma-debug.c: fix __hash_bucket_find
>
> If there is only one match, the unique matched entry should be returned.
>
> Without the fix, the commit f62566214fe31c9f9b3218a42f1b19e6a9e6844a
>
> dma-debug: new interfaces to debug dma mapping errors
>
> can't work reliably because only device and dma_addr are passed to
> dma_mapping_error().
>
> Cc: Joerg Roedel <joerg.roedel@xxxxxxx>
> Cc: Shuah Khan <shuah.khan@xxxxxx>
> Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Jakub Kicinski <kubakici@xxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> ---
> lib/dma-debug.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/dma-debug.c b/lib/dma-debug.c
> index 94aa94e..59f4a1a 100644
> --- a/lib/dma-debug.c
> +++ b/lib/dma-debug.c
> @@ -277,7 +277,7 @@ static struct dma_debug_entry
> *__hash_bucket_find(struct hash_bucket *bucket,
> match_fn match)
> {
> struct dma_debug_entry *entry, *ret = NULL;
> - int matches = 0, match_lvl, last_lvl = 0;
> + int matches = 0, match_lvl, last_lvl = -1;
>
> list_for_each_entry(entry, &bucket->list, list) {
> if (!match(ref, entry))
> @@ -306,7 +306,7 @@ static struct dma_debug_entry
> *__hash_bucket_find(struct hash_bucket *bucket,
> } else if (match_lvl > last_lvl) {
> /*
> * We found an entry that fits better then the
> - * previous one
> + * previous one or it is the 1st match.
> */
> last_lvl = match_lvl;
> ret = entry;

Thanks for finding and fixing the problem. This fixes the problem
Fengguang Wu reported: adding him to the thread.

https://lkml.org/lkml/2012/10/14/233

I have a reliable test case and test system that reproduces the problem.
Re-tested it with and without patch and didn't see the warning with your
patch.

That said, this patch is malformed and didn't apply cleanly.
You have my

Tested-by: Shuah Khan <shuah.khan@xxxxxx>

Thanks,
-- Shuah


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