Messages in this thread | | | Subject | Re: [PATCH v3 2/3] block: introduce new field bd_flags in block_device | From | Yu Kuai <> | Date | Wed, 22 Nov 2023 15:06:23 +0800 |
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Hi,
在 2023/11/22 11:52, Michael Kelley 写道: > From: Yu Kuai <yukuai1@huaweicloud.com> Sent: Wednesday, November 22, 2023 2:31 AM >> >> There are multiple switches in struct block_device, use separate bool >> fields for them is not gracefully. Add a new field bd_flags and replace >> swithes to a bit, there are no functional changes, and prepare to add >> a new switch in the next patch. In order to keep bd_flags in the first >> cacheline and prevent layout to be affected, define it as u16. >> >> Also add new helpers to set/clear/test each bit like 'bio->bi_flags'. >> >> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >> --- >> block/bdev.c | 15 ++++++++------- >> block/blk-core.c | 7 ++++--- >> block/genhd.c | 15 +++++++++++---- >> block/ioctl.c | 6 +++++- >> include/linux/blk_types.h | 27 +++++++++++++++++++++------ >> include/linux/blkdev.h | 5 +++-- >> 6 files changed, 52 insertions(+), 23 deletions(-) >> >> diff --git a/block/bdev.c b/block/bdev.c >> index e4cfb7adb645..10f524a7416c 100644 >> --- a/block/bdev.c >> +++ b/block/bdev.c >> @@ -402,10 +402,10 @@ struct block_device *bdev_alloc(struct gendisk >> *disk, u8 partno) >> bdev->bd_partno = partno; >> bdev->bd_inode = inode; >> bdev->bd_queue = disk->queue; >> - if (partno) >> - bdev->bd_has_submit_bio = disk->part0->bd_has_submit_bio; >> + if (partno && bdev_flagged(disk->part0, BD_FLAG_HAS_SUBMIT_BIO)) >> + bdev_set_flag(bdev, BD_FLAG_HAS_SUBMIT_BIO); >> else >> - bdev->bd_has_submit_bio = false; >> + bdev_clear_flag(bdev, BD_FLAG_HAS_SUBMIT_BIO); >> bdev->bd_stats = alloc_percpu(struct disk_stats); >> if (!bdev->bd_stats) { >> iput(inode); >> @@ -606,7 +606,7 @@ static void bd_end_claim(struct block_device *bdev, void *holder) >> bdev->bd_holder = NULL; >> bdev->bd_holder_ops = NULL; >> mutex_unlock(&bdev->bd_holder_lock); >> - if (bdev->bd_write_holder) >> + if (bdev_flagged(bdev, BD_FLAG_WRITE_HOLDER)) >> unblock = true; >> } >> if (!whole->bd_holders) >> @@ -619,7 +619,7 @@ static void bd_end_claim(struct block_device *bdev, void *holder) >> */ >> if (unblock) { >> disk_unblock_events(bdev->bd_disk); >> - bdev->bd_write_holder = false; >> + bdev_clear_flag(bdev, BD_FLAG_WRITE_HOLDER); >> } >> } >> >> @@ -805,9 +805,10 @@ struct block_device *blkdev_get_by_dev(dev_t dev, >> blk_mode_t mode, void *holder, >> * writeable reference is too fragile given the way @mode is >> * used in blkdev_get/put(). >> */ >> - if ((mode & BLK_OPEN_WRITE) && !bdev->bd_write_holder && >> + if ((mode & BLK_OPEN_WRITE) && >> + !bdev_flagged(bdev, BD_FLAG_WRITE_HOLDER) && >> (disk->event_flags & DISK_EVENT_FLAG_BLOCK_ON_EXCL_WRITE)) { >> - bdev->bd_write_holder = true; >> + bdev_set_flag(bdev, BD_FLAG_WRITE_HOLDER); >> unblock_events = false; >> } >> } >> diff --git a/block/blk-core.c b/block/blk-core.c >> index fdf25b8d6e78..f9f8b12ba626 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -482,7 +482,8 @@ __setup("fail_make_request=", >> setup_fail_make_request); >> >> bool should_fail_request(struct block_device *part, unsigned int bytes) >> { >> - return part->bd_make_it_fail && should_fail(&fail_make_request, bytes); >> + return bdev_flagged(part, BD_FLAG_MAKE_IT_FAIL) && >> + should_fail(&fail_make_request, bytes); >> } >> >> static int __init fail_make_request_debugfs(void) >> @@ -595,7 +596,7 @@ static void __submit_bio(struct bio *bio) >> if (unlikely(!blk_crypto_bio_prep(&bio))) >> return; >> >> - if (!bio->bi_bdev->bd_has_submit_bio) { >> + if (!bdev_flagged(bio->bi_bdev, BD_FLAG_HAS_SUBMIT_BIO)) { >> blk_mq_submit_bio(bio); >> } else if (likely(bio_queue_enter(bio) == 0)) { >> struct gendisk *disk = bio->bi_bdev->bd_disk; >> @@ -703,7 +704,7 @@ void submit_bio_noacct_nocheck(struct bio *bio) >> */ >> if (current->bio_list) >> bio_list_add(¤t->bio_list[0], bio); >> - else if (!bio->bi_bdev->bd_has_submit_bio) >> + else if (!bdev_flagged(bio->bi_bdev, BD_FLAG_HAS_SUBMIT_BIO)) >> __submit_bio_noacct_mq(bio); >> else >> __submit_bio_noacct(bio); >> diff --git a/block/genhd.c b/block/genhd.c >> index c9d06f72c587..57f96c0c8da0 100644 >> --- a/block/genhd.c >> +++ b/block/genhd.c >> @@ -413,7 +413,8 @@ int __must_check device_add_disk(struct device >> *parent, struct gendisk *disk, >> elevator_init_mq(disk->queue); >> >> /* Mark bdev as having a submit_bio, if needed */ >> - disk->part0->bd_has_submit_bio = disk->fops->submit_bio != NULL; >> + if (disk->fops->submit_bio) >> + bdev_set_flag(disk->part0, BD_FLAG_HAS_SUBMIT_BIO); >> >> /* >> * If the driver provides an explicit major number it also must provide >> @@ -1062,7 +1063,8 @@ static DEVICE_ATTR(diskseq, 0444, diskseq_show, NULL); >> ssize_t part_fail_show(struct device *dev, >> struct device_attribute *attr, char *buf) >> { >> - return sprintf(buf, "%d\n", dev_to_bdev(dev)->bd_make_it_fail); >> + return sprintf(buf, "%d\n", >> + bdev_flagged(dev_to_bdev(dev), BD_FLAG_MAKE_IT_FAIL)); >> } >> >> ssize_t part_fail_store(struct device *dev, >> @@ -1071,8 +1073,13 @@ ssize_t part_fail_store(struct device *dev, >> { >> int i; >> >> - if (count > 0 && sscanf(buf, "%d", &i) > 0) >> - dev_to_bdev(dev)->bd_make_it_fail = i; >> + if (count > 0 && sscanf(buf, "%d", &i) > 0) { >> + if (!i) >> + bdev_clear_flag(dev_to_bdev(dev), BD_FLAG_MAKE_IT_FAIL); >> + else >> + bdev_set_flag(dev_to_bdev(dev), BD_FLAG_MAKE_IT_FAIL); >> + >> + } >> >> return count; >> } >> diff --git a/block/ioctl.c b/block/ioctl.c >> index 4160f4e6bd5b..a64440f4c96b 100644 >> --- a/block/ioctl.c >> +++ b/block/ioctl.c >> @@ -394,7 +394,11 @@ static int blkdev_roset(struct block_device *bdev, unsigned cmd, >> if (ret) >> return ret; >> } >> - bdev->bd_read_only = n; >> + >> + if (!n) >> + bdev_clear_flag(bdev, BD_FLAG_READ_ONLY); >> + else >> + bdev_set_flag(bdev, BD_FLAG_READ_ONLY); >> return 0; >> } >> >> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h >> index f7d40692dd94..de652045111b 100644 >> --- a/include/linux/blk_types.h >> +++ b/include/linux/blk_types.h >> @@ -37,6 +37,11 @@ struct bio_crypt_ctx; >> #define PAGE_SECTORS (1 << PAGE_SECTORS_SHIFT) >> #define SECTOR_MASK (PAGE_SECTORS - 1) >> >> +#define BD_FLAG_READ_ONLY 0 /* read-only-policy */ >> +#define BD_FLAG_WRITE_HOLDER 1 >> +#define BD_FLAG_HAS_SUBMIT_BIO 2 >> +#define BD_FLAG_MAKE_IT_FAIL 3 >> + >> struct block_device { >> sector_t bd_start_sect; >> sector_t bd_nr_sectors; >> @@ -44,10 +49,8 @@ struct block_device { >> struct request_queue * bd_queue; >> struct disk_stats __percpu *bd_stats; >> unsigned long bd_stamp; >> - bool bd_read_only; /* read-only policy */ >> + unsigned short bd_flags; >> u8 bd_partno; >> - bool bd_write_holder; >> - bool bd_has_submit_bio; >> dev_t bd_dev; >> struct inode *bd_inode; /* will die */ >> >> @@ -67,9 +70,6 @@ struct block_device { >> struct super_block *bd_fsfreeze_sb; >> >> struct partition_meta_info *bd_meta_info; >> -#ifdef CONFIG_FAIL_MAKE_REQUEST >> - bool bd_make_it_fail; >> -#endif >> /* >> * keep this out-of-line as it's both big and not needed in the fast >> * path >> @@ -86,6 +86,21 @@ struct block_device { >> #define bdev_kobj(_bdev) \ >> (&((_bdev)->bd_device.kobj)) >> >> +static inline bool bdev_flagged(struct block_device *bdev, unsigned int bit) >> +{ >> + return bdev->bd_flags & (1U << bit); >> +} >> + >> +static inline void bdev_set_flag(struct block_device *bdev, unsigned int bit) >> +{ >> + bdev->bd_flags |= (1U << bit); >> +} >> + >> +static inline void bdev_clear_flag(struct block_device *bdev, unsigned int bit) >> +{ >> + bdev->bd_flags &= ~(1U << bit); >> +} > > It seems like there's atomicity problem with this approach. In the above > code, setting and clearing a bd_flag is *not* atomic with respect to > setting/clearing some other bd_flag. For example, setting/clearing > BD_FLAG_MAKE_IT_FAIL via the /sys interface could race with > setting/clearing BD_FLAG_READ_ONLY via an ioctl, and one of the > two changes could be lost. This problem wouldn't happen when > each flag was a separate field. Admittedly, the likelihood of a > problem with BD_FLAG_MAKE_IT_FAIL is extremely low, but > conceptually the lack of atomicity is still wrong. There might > be a similar problem with BD_FLAG_WRITE_HOLDER, but I > didn't investigate thoroughly.
Thanks for the explanation, however, currently bio->bi_opf, bio->bi_flags and req->rq_flags, and I can't understand now how do they prevent to change bit concurrently? I'm probably missing something...
Thanks, Kuai
> > Michael > >> + >> /* >> * Block error status values. See block/blk-core:blk_errors for the details. >> * Alpha cannot write a byte atomically, so we need to use 32-bit value. >> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h >> index 51fa7ffdee83..fc1d55ef5107 100644 >> --- a/include/linux/blkdev.h >> +++ b/include/linux/blkdev.h >> @@ -741,13 +741,14 @@ void disk_uevent(struct gendisk *disk, enum >> kobject_action action); >> >> static inline int get_disk_ro(struct gendisk *disk) >> { >> - return disk->part0->bd_read_only || >> + return bdev_flagged(disk->part0, BD_FLAG_READ_ONLY) || >> test_bit(GD_READ_ONLY, &disk->state); >> } >> >> static inline int bdev_read_only(struct block_device *bdev) >> { >> - return bdev->bd_read_only || get_disk_ro(bdev->bd_disk); >> + return bdev_flagged(bdev, BD_FLAG_READ_ONLY) || >> + get_disk_ro(bdev->bd_disk); >> } >> >> bool set_capacity_and_notify(struct gendisk *disk, sector_t size); >> -- >> 2.39.2 > > . >
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