On 05/27/2014 07:24 PM, Maurizio Lombardi wrote:
> On Tue, May 27, 2014 at 10:43:59AM +0200, Maurizio Lombardi wrote:
>>
>> But now I'm suspicious of this part of commit 3979ef4dcf:
>>
>> failed:
>> bvec->bv_page = NULL;
>> bvec->bv_len = 0;
>> bvec->bv_offset = 0;
>> bio->bi_vcnt--; <----------------
>> blk_recount_segments(q, bio);
>> return 0;
>>
>> Is decreasing bi_vcnt sufficient to guarantee that blk_recount_segments()
>> recalculates the correct number of physical segments?
>> Looking at the __blk_recalc_rq_segments() it appears it may not be the case.
>>
>> The question is how can we restore the correct number of physical segments
>> in case
>> of failure without breaking anything...
>>
>
> If my hypothesis is correct, the following patch should trigger a kernel
> panic,
> Jet Chen, can you try it and let me know whether the BUG_ON is hit or not?
Sorry for late respond. Dongsu has sent a patch for this issue.
message-id
<1401289778-9840-1-git-send-email-dongsu.p...@profitbricks.com>
Do you still need me to test the following patch ?
>
> diff --git a/block/bio.c b/block/bio.c
> index 0443694..763868f 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -701,6 +701,7 @@ static int __bio_add_page(struct request_queue *q, struct
> bio *bio, struct page
> unsigned int max_sectors)
> {
> int retried_segments = 0;
> + unsigned int phys_segments_orig;
> struct bio_vec *bvec;
>
> /*
> @@ -751,6 +752,9 @@ static int __bio_add_page(struct request_queue *q, struct
> bio *bio, struct page
> if (bio->bi_vcnt >= bio->bi_max_vecs)
> return 0;
>
> + blk_recount_segments(q, bio);
> + phys_segments_orig = bio->bi_phys_segments;
> +
> /*
> * setup the new entry, we might clear it again later if we
> * cannot add the page
> @@ -811,6 +815,7 @@ static int __bio_add_page(struct request_queue *q, struct
> bio *bio, struct page
> bvec->bv_offset = 0;
> bio->bi_vcnt--;
> blk_recount_segments(q, bio);
> + BUG_ON(phys_segments_orig != bio->bi_phys_segments);
> return 0;
> }
>
>
> Regards,
> Maurizio Lombardi
>
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