* Re: [PATCH] iomap: Fix the write_count in iomap_add_to_ioend().
2020-08-21 6:07 ` [PATCH] iomap: Fix the write_count in iomap_add_to_ioend() Christoph Hellwig
@ 2020-08-21 8:53 ` Ritesh Harjani
2020-08-21 14:49 ` Jens Axboe
1 sibling, 0 replies; 3+ messages in thread
From: Ritesh Harjani @ 2020-08-21 8:53 UTC (permalink / raw)
To: Christoph Hellwig, Anju T Sudhakar, linux-block
Cc: darrick.wong, linux-xfs, linux-fsdevel, linux-kernel, willy
On 8/21/20 11:37 AM, Christoph Hellwig wrote:
> On Wed, Aug 19, 2020 at 03:58:41PM +0530, Anju T Sudhakar wrote:
>> From: Ritesh Harjani <riteshh@linux.ibm.com>
>>
>> __bio_try_merge_page() may return same_page = 1 and merged = 0.
>> This could happen when bio->bi_iter.bi_size + len > UINT_MAX.
>> Handle this case in iomap_add_to_ioend() by incrementing write_count.
>> This scenario mostly happens where we have too much dirty data accumulated.
>>
>> w/o the patch we hit below kernel warning,
>
> I think this is better fixed in the block layer rather than working
> around the problem in the callers. Something like this:
>
> diff --git a/block/bio.c b/block/bio.c
> index c63ba04bd62967..ef321cd1072e4e 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -879,8 +879,10 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
> struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
>
> if (page_is_mergeable(bv, page, len, off, same_page)) {
> - if (bio->bi_iter.bi_size > UINT_MAX - len)
> + if (bio->bi_iter.bi_size > UINT_MAX - len) {
> + *same_page = false;
> return false;
> + }
> bv->bv_len += len;
> bio->bi_iter.bi_size += len;
> return true;
>
Ya, we had think of that. But what we then thought was, maybe the
API does return the right thing. Meaning, what API says is, same_page is
true, but the page couldn't be merged hence it returned ret = false.
With that thought, we fixed this in the caller.
But agree with you that with ret = false, there is no meaning of
same_page being true. Ok, so let linux-block comment on whether
above also looks good. If yes, I can spin out an official patch with
all details.
-ritesh
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] iomap: Fix the write_count in iomap_add_to_ioend().
2020-08-21 6:07 ` [PATCH] iomap: Fix the write_count in iomap_add_to_ioend() Christoph Hellwig
2020-08-21 8:53 ` Ritesh Harjani
@ 2020-08-21 14:49 ` Jens Axboe
1 sibling, 0 replies; 3+ messages in thread
From: Jens Axboe @ 2020-08-21 14:49 UTC (permalink / raw)
To: Christoph Hellwig, Anju T Sudhakar
Cc: darrick.wong, linux-xfs, linux-fsdevel, linux-kernel, willy,
riteshh, linux-block
On 8/21/20 12:07 AM, Christoph Hellwig wrote:
> On Wed, Aug 19, 2020 at 03:58:41PM +0530, Anju T Sudhakar wrote:
>> From: Ritesh Harjani <riteshh@linux.ibm.com>
>>
>> __bio_try_merge_page() may return same_page = 1 and merged = 0.
>> This could happen when bio->bi_iter.bi_size + len > UINT_MAX.
>> Handle this case in iomap_add_to_ioend() by incrementing write_count.
>> This scenario mostly happens where we have too much dirty data accumulated.
>>
>> w/o the patch we hit below kernel warning,
>
> I think this is better fixed in the block layer rather than working
> around the problem in the callers. Something like this:
>
> diff --git a/block/bio.c b/block/bio.c
> index c63ba04bd62967..ef321cd1072e4e 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -879,8 +879,10 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
> struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
>
> if (page_is_mergeable(bv, page, len, off, same_page)) {
> - if (bio->bi_iter.bi_size > UINT_MAX - len)
> + if (bio->bi_iter.bi_size > UINT_MAX - len) {
> + *same_page = false;
> return false;
> + }
> bv->bv_len += len;
> bio->bi_iter.bi_size += len;
> return true;
>
This looks good to me.
--
Jens Axboe
^ permalink raw reply [flat|nested] 3+ messages in thread