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Message-ID: <dffa941d-63b5-2068-80f4-dd012f520147@huawei.com>
Date: Fri, 19 Mar 2021 10:15:18 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Gao Xiang <hsiangkao@....com>, <linux-erofs@...ts.ozlabs.org>,
Chao Yu <chao@...nel.org>
CC: <linux-kernel@...r.kernel.org>, Gao Xiang <hsiangkao@...hat.com>,
"Martin DEVERA" <devik@...labs.cz>
Subject: Re: [PATCH v2] erofs: fix bio->bi_max_vecs behavior change
On 2021/3/6 12:04, Gao Xiang wrote:
> From: Gao Xiang <hsiangkao@...hat.com>
>
> Martin reported an issue that directory read could be hung on the
> latest -rc kernel with some certain image. The root cause is that
> commit baa2c7c97153 ("block: set .bi_max_vecs as actual allocated
> vector number") changes .bi_max_vecs behavior. bio->bi_max_vecs
> is set as actual allocated vector number rather than the requested
> number now.
>
> Let's avoid using .bi_max_vecs completely instead.
>
> Reported-by: Martin DEVERA <devik@...labs.cz>
> Signed-off-by: Gao Xiang <hsiangkao@...hat.com>
> ---
> change since v1:
> - since bio->bi_max_vecs doesn't record extent blocks anymore,
> introduce a remaining extent block to avoid extent excess.
>
> fs/erofs/data.c | 28 +++++++++++-----------------
> 1 file changed, 11 insertions(+), 17 deletions(-)
>
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index f88851c5c250..1249e74b3bf0 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -129,6 +129,7 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
> struct page *page,
> erofs_off_t *last_block,
> unsigned int nblocks,
> + unsigned int *eblks,
> bool ra)
> {
> struct inode *const inode = mapping->host;
> @@ -145,8 +146,7 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
>
> /* note that for readpage case, bio also equals to NULL */
> if (bio &&
> - /* not continuous */
> - *last_block + 1 != current_block) {
> + (*last_block + 1 != current_block || !*eblks)) {
Xiang,
I found below function during checking bi_max_vecs usage in f2fs:
/**
* bio_full - check if the bio is full
* @bio: bio to check
* @len: length of one segment to be added
*
* Return true if @bio is full and one segment with @len bytes can't be
* added to the bio, otherwise return false
*/
static inline bool bio_full(struct bio *bio, unsigned len)
{
if (bio->bi_vcnt >= bio->bi_max_vecs)
return true;
if (bio->bi_iter.bi_size > UINT_MAX - len)
return true;
return false;
}
Could you please check that whether it will be better to use bio_full()
rather than using left-space-in-bio maintained by erofs itself? something
like:
if (bio && (bio_full(bio, PAGE_SIZE) ||
/* not continuous */
(*last_block + 1 != current_block))
I'm thinking we need to decouple bio detail implementation as much as
possible, to avoid regression whenever bio used/max size definition
updates, though I've no idea how to fix f2fs case.
Let me know if you have other concern.
Thanks,
> submit_bio_retry:
> submit_bio(bio);
> bio = NULL;
> @@ -216,7 +216,8 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
> if (nblocks > DIV_ROUND_UP(map.m_plen, PAGE_SIZE))
> nblocks = DIV_ROUND_UP(map.m_plen, PAGE_SIZE);
>
> - bio = bio_alloc(GFP_NOIO, bio_max_segs(nblocks));
> + *eblks = bio_max_segs(nblocks);
> + bio = bio_alloc(GFP_NOIO, *eblks);
>
> bio->bi_end_io = erofs_readendio;
> bio_set_dev(bio, sb->s_bdev);
> @@ -229,16 +230,8 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
> /* out of the extent or bio is full */
> if (err < PAGE_SIZE)
> goto submit_bio_retry;
> -
> + --*eblks;
> *last_block = current_block;
> -
> - /* shift in advance in case of it followed by too many gaps */
> - if (bio->bi_iter.bi_size >= bio->bi_max_vecs * PAGE_SIZE) {
> - /* err should reassign to 0 after submitting */
> - err = 0;
> - goto submit_bio_out;
> - }
> -
> return bio;
>
> err_out:
> @@ -252,7 +245,6 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
>
> /* if updated manually, continuous pages has a gap */
> if (bio)
> -submit_bio_out:
> submit_bio(bio);
> return err ? ERR_PTR(err) : NULL;
> }
> @@ -264,23 +256,26 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio,
> static int erofs_raw_access_readpage(struct file *file, struct page *page)
> {
> erofs_off_t last_block;
> + unsigned int eblks;
> struct bio *bio;
>
> trace_erofs_readpage(page, true);
>
> bio = erofs_read_raw_page(NULL, page->mapping,
> - page, &last_block, 1, false);
> + page, &last_block, 1, &eblks, false);
>
> if (IS_ERR(bio))
> return PTR_ERR(bio);
>
> - DBG_BUGON(bio); /* since we have only one bio -- must be NULL */
> + if (bio)
> + submit_bio(bio);
> return 0;
> }
>
> static void erofs_raw_access_readahead(struct readahead_control *rac)
> {
> erofs_off_t last_block;
> + unsigned int eblks;
> struct bio *bio = NULL;
> struct page *page;
>
> @@ -291,7 +286,7 @@ static void erofs_raw_access_readahead(struct readahead_control *rac)
> prefetchw(&page->flags);
>
> bio = erofs_read_raw_page(bio, rac->mapping, page, &last_block,
> - readahead_count(rac), true);
> + readahead_count(rac), &eblks, true);
>
> /* all the page errors are ignored when readahead */
> if (IS_ERR(bio)) {
> @@ -305,7 +300,6 @@ static void erofs_raw_access_readahead(struct readahead_control *rac)
> put_page(page);
> }
>
> - /* the rare case (end in gaps) */
> if (bio)
> submit_bio(bio);
> }
>
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