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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH v6 11/34] iov_iter, block: Make bio structs pin pages rather than ref'ing if appropriate From: David Howells To: Al Viro Cc: Jens Axboe , Jan Kara , Christoph Hellwig , Matthew Wilcox , Logan Gunthorpe , linux-block@vger.kernel.org, dhowells@redhat.com, Christoph Hellwig , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Date: Mon, 16 Jan 2023 23:09:20 +0000 Message-ID: <167391056047.2311931.6772604381276147664.stgit@warthog.procyon.org.uk> In-Reply-To: <167391047703.2311931.8115712773222260073.stgit@warthog.procyon.org.uk> References: <167391047703.2311931.8115712773222260073.stgit@warthog.procyon.org.uk> User-Agent: StGit/1.5 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Convert the block layer's bio code to use iov_iter_extract_pages() instead of iov_iter_get_pages(). This will pin pages or leave them unaltered rather than getting a ref on them as appropriate to the source iterator. The pages need to be pinned for DIO-read rather than having refs taken on them to prevent VM copy-on-write from malfunctioning during a concurrent fork() (the result of the I/O would otherwise end up only visible to the child process and not the parent). To implement this: (1) If the BIO_PAGE_REFFED flag is set, this causes attached pages to be passed to put_page() during cleanup. (2) A BIO_PAGE_PINNED flag is provided. If set, this causes attached pages to be passed to unpin_user_page() during cleanup. (3) BIO_PAGE_REFFED is set by default and BIO_PAGE_PINNED is cleared by default when the bio is (re-)initialised. (4) If iov_iter_extract_pages() indicates FOLL_GET, this causes BIO_PAGE_REFFED to be set and if FOLL_PIN is indicated, this causes BIO_PAGE_PINNED to be set. If it returns neither FOLL_* flag, then both BIO_PAGE_* flags will be cleared. Mixing sets of pages with different clean up modes is not supported. (5) Cloned bio structs have both flags cleared. (6) bio_release_pages() will do the release if either BIO_PAGE_* flag is set. [!] Note that this is tested a bit with ext4, but nothing else. Changes ======= ver #5) - Transcribe the FOLL_* flags returned by iov_iter_extract_pages() to BIO_* flags and got rid of bi_cleanup_mode. - Replaced BIO_NO_PAGE_REF to BIO_PAGE_REFFED in the preceding patch. Signed-off-by: David Howells cc: Al Viro cc: Jens Axboe cc: Jan Kara cc: Christoph Hellwig cc: Matthew Wilcox cc: Logan Gunthorpe cc: linux-block@vger.kernel.org Link: https://lore.kernel.org/r/167305166150.1521586.10220949115402059720.stgit@warthog.procyon.org.uk/ # v4 Link: https://lore.kernel.org/r/167344731521.2425628.5403113335062567245.stgit@warthog.procyon.org.uk/ # v5 --- block/bio.c | 34 +++++++++++++++++++--------------- block/blk-map.c | 22 +++++++++++----------- block/blk.h | 25 +++++++++++++++++++++++++ include/linux/bio.h | 3 ++- 4 files changed, 57 insertions(+), 27 deletions(-) diff --git a/block/bio.c b/block/bio.c index d8c636cefcdd..f9ee3625d65c 100644 --- a/block/bio.c +++ b/block/bio.c @@ -245,8 +245,9 @@ static void bio_free(struct bio *bio) * when IO has completed, or when the bio is released. * * We set the initial assumption that pages attached to the bio will be - * released with put_page() by setting BIO_PAGE_REFFED; if the pages - * should not be put, this flag should be cleared. + * released with put_page() by setting BIO_PAGE_REFFED, but this should be set + * to BIO_PAGE_PINNED if the page should be unpinned instead; if the pages + * should not be put or unpinned, these flags should be cleared. */ void bio_init(struct bio *bio, struct block_device *bdev, struct bio_vec *table, unsigned short max_vecs, blk_opf_t opf) @@ -819,6 +820,7 @@ static int __bio_clone(struct bio *bio, struct bio *bio_src, gfp_t gfp) { bio_set_flag(bio, BIO_CLONED); bio_clear_flag(bio, BIO_PAGE_REFFED); + bio_clear_flag(bio, BIO_PAGE_PINNED); bio->bi_ioprio = bio_src->bi_ioprio; bio->bi_iter = bio_src->bi_iter; @@ -1183,7 +1185,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty) bio_for_each_segment_all(bvec, bio, iter_all) { if (mark_dirty && !PageCompound(bvec->bv_page)) set_page_dirty_lock(bvec->bv_page); - put_page(bvec->bv_page); + bio_release_page(bio, bvec->bv_page); } } EXPORT_SYMBOL_GPL(__bio_release_pages); @@ -1220,7 +1222,7 @@ static int bio_iov_add_page(struct bio *bio, struct page *page, } if (same_page) - put_page(page); + bio_release_page(bio, page); return 0; } @@ -1234,7 +1236,7 @@ static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page, queue_max_zone_append_sectors(q), &same_page) != len) return -EINVAL; if (same_page) - put_page(page); + bio_release_page(bio, page); return 0; } @@ -1245,10 +1247,10 @@ static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page, * @bio: bio to add pages to * @iter: iov iterator describing the region to be mapped * - * Pins pages from *iter and appends them to @bio's bvec array. The - * pages will have to be released using put_page() when done. - * For multi-segment *iter, this function only adds pages from the - * next non-empty segment of the iov iterator. + * Extracts pages from *iter and appends them to @bio's bvec array. The pages + * will have to be cleaned up in the way indicated by the BIO_PAGE_REFFED and + * BIO_PAGE_PINNED flags. For a multi-segment *iter, this function only adds + * pages from the next non-empty segment of the iov iterator. * * The I/O direction is determined from the bio operation type. */ @@ -1284,12 +1286,14 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) * result to ensure the bio's total size is correct. The remainder of * the iov data will be picked up in the next bio iteration. */ - size = iov_iter_get_pages(iter, pages, - UINT_MAX - bio->bi_iter.bi_size, - nr_pages, &offset, gup_flags); + size = iov_iter_extract_pages(iter, &pages, + UINT_MAX - bio->bi_iter.bi_size, + nr_pages, gup_flags, &offset); if (unlikely(size <= 0)) return size ? size : -EFAULT; + bio_set_cleanup_mode(bio, iter, gup_flags); + nr_pages = DIV_ROUND_UP(offset + size, PAGE_SIZE); trim = size & (bdev_logical_block_size(bio->bi_bdev) - 1); @@ -1319,7 +1323,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) iov_iter_revert(iter, left); out: while (i < nr_pages) - put_page(pages[i++]); + bio_release_page(bio, pages[i++]); return ret; } @@ -1502,8 +1506,8 @@ void bio_set_pages_dirty(struct bio *bio) * the BIO and re-dirty the pages in process context. * * It is expected that bio_check_pages_dirty() will wholly own the BIO from - * here on. It will run one put_page() against each page and will run one - * bio_put() against the BIO. + * here on. It will run one put_page() or unpin_user_page() against each page + * and will run one bio_put() against the BIO. */ static void bio_dirty_fn(struct work_struct *work); diff --git a/block/blk-map.c b/block/blk-map.c index c30be529fb55..be769f889eca 100644 --- a/block/blk-map.c +++ b/block/blk-map.c @@ -285,24 +285,24 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter, gup_flags |= FOLL_PCI_P2PDMA; while (iov_iter_count(iter)) { - struct page **pages, *stack_pages[UIO_FASTIOV]; + struct page *stack_pages[UIO_FASTIOV]; + struct page **pages = stack_pages; ssize_t bytes; size_t offs; int npages; - if (nr_vecs <= ARRAY_SIZE(stack_pages)) { - pages = stack_pages; - bytes = iov_iter_get_pages(iter, pages, LONG_MAX, - nr_vecs, &offs, gup_flags); - } else { - bytes = iov_iter_get_pages_alloc(iter, &pages, - LONG_MAX, &offs, gup_flags); - } + if (nr_vecs > ARRAY_SIZE(stack_pages)) + pages = NULL; + + bytes = iov_iter_extract_pages(iter, &pages, LONG_MAX, + nr_vecs, gup_flags, &offs); if (unlikely(bytes <= 0)) { ret = bytes ? bytes : -EFAULT; goto out_unmap; } + bio_set_cleanup_mode(bio, iter, gup_flags); + npages = DIV_ROUND_UP(offs + bytes, PAGE_SIZE); if (unlikely(offs & queue_dma_alignment(rq->q))) @@ -319,7 +319,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter, if (!bio_add_hw_page(rq->q, bio, page, n, offs, max_sectors, &same_page)) { if (same_page) - put_page(page); + bio_release_page(bio, page); break; } @@ -331,7 +331,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter, * release the pages we didn't map into the bio, if any */ while (j < npages) - put_page(pages[j++]); + bio_release_page(bio, pages[j++]); if (pages != stack_pages) kvfree(pages); /* couldn't stuff something into bio? */ diff --git a/block/blk.h b/block/blk.h index 4c3b3325219a..29f12f758915 100644 --- a/block/blk.h +++ b/block/blk.h @@ -425,6 +425,31 @@ int bio_add_hw_page(struct request_queue *q, struct bio *bio, struct page *page, unsigned int len, unsigned int offset, unsigned int max_sectors, bool *same_page); +/* + * Set the cleanup mode for a bio from an iterator and the GUP flags. + */ +static inline void bio_set_cleanup_mode(struct bio *bio, struct iov_iter *iter, + unsigned int gup_flags) +{ + unsigned int cleanup_mode; + + bio_clear_flag(bio, BIO_PAGE_REFFED); + cleanup_mode = iov_iter_extract_mode(iter, gup_flags); + if (cleanup_mode & FOLL_GET) + bio_set_flag(bio, BIO_PAGE_REFFED); + if (cleanup_mode & FOLL_PIN) + bio_set_flag(bio, BIO_PAGE_PINNED); +} + +/* + * Clean up a page appropriately, where the page may be pinned, may have a + * ref taken on it or neither. + */ +static inline void bio_release_page(struct bio *bio, struct page *page) +{ + page_put_unpin(page, bio->bi_flags & (FOLL_GET | FOLL_PIN)); +} + struct request_queue *blk_alloc_queue(int node_id); int disk_scan_partitions(struct gendisk *disk, fmode_t mode, void *owner); diff --git a/include/linux/bio.h b/include/linux/bio.h index 69b32c5532f6..856b28e41d24 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -496,7 +496,8 @@ void zero_fill_bio(struct bio *bio); static inline void bio_release_pages(struct bio *bio, bool mark_dirty) { - if (bio_flagged(bio, BIO_PAGE_REFFED)) + if (bio_flagged(bio, BIO_PAGE_REFFED) || + bio_flagged(bio, BIO_PAGE_PINNED)) __bio_release_pages(bio, mark_dirty); }