Re: [PATCH] block: read i_size with i_size_read()

From: Neil Brown
Date: Fri Nov 05 2010 - 15:38:26 EST

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On Fri, 5 Nov 2010 15:27:21 -0400
Mike Snitzer <snitzer@xxxxxxxxxx> wrote:

> Convert direct reads of an inode's i_size to using i_size_read().
>
> i_size_{read,write} use a seqcount to protect reads from accessing
> incomple writes. Concurrent i_size_write()s require mutual exclussion
> to protect the seqcount that is used by i_size_{read,write}. But
> i_size_read() callers do not need to use additional locking.
>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: Jens Axboe <jaxboe@xxxxxxxxxxxx>
> Cc: Neil Brown <neilb@xxxxxxx>
> Cc: drbd-dev@xxxxxxxxxxxxxxxx

MD bits
Acked-by: NeilBrown <neilb@xxxxxxx>

It is of course OK to read i_size when you hold the appropriate mutex,
but we don't in any of these cases.

Thanks,
NeilBrown

> ---
> block/blk-core.c | 4 ++--
> block/compat_ioctl.c | 4 ++--
> block/ioctl.c | 6 +++---
> drivers/block/drbd/drbd_int.h | 2 +-
> drivers/md/md.c | 18 +++++++++---------
> 5 files changed, 17 insertions(+), 17 deletions(-)
>
> NOTE: I stopped short of fixing drbd and nbd to use revalidate_disk
> and/or i_size_write. I also have no intention of auditing all the
> direct i_size readers/writers in fs/, maybe others will have an
> interest.
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index f0834e2..17fcb83 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1351,7 +1351,7 @@ static void handle_bad_sector(struct bio *bio)
> bdevname(bio->bi_bdev, b),
> bio->bi_rw,
> (unsigned long long)bio->bi_sector +
> bio_sectors(bio),
> - (long long)(bio->bi_bdev->bd_inode->i_size
> >> 9));
> + (long
> long)(i_size_read(bio->bi_bdev->bd_inode) >> 9));
> set_bit(BIO_EOF, &bio->bi_flags);
> }
> @@ -1404,7 +1404,7 @@ static inline int bio_check_eod(struct bio
> *bio, unsigned int nr_sectors) return 0;
>
> /* Test device or partition size, when known. */
> - maxsector = bio->bi_bdev->bd_inode->i_size >> 9;
> + maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
> if (maxsector) {
> sector_t sector = bio->bi_sector;
>
> diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
> index 119f07b..58c6ee5 100644
> --- a/block/compat_ioctl.c
> +++ b/block/compat_ioctl.c
> @@ -744,13 +744,13 @@ long compat_blkdev_ioctl(struct file *file,
> unsigned cmd, unsigned long arg) bdi->ra_pages = (arg * 512) /
> PAGE_CACHE_SIZE; return 0;
> case BLKGETSIZE:
> - size = bdev->bd_inode->i_size;
> + size = i_size_read(bdev->bd_inode);
> if ((size >> 9) > ~0UL)
> return -EFBIG;
> return compat_put_ulong(arg, size >> 9);
>
> case BLKGETSIZE64_32:
> - return compat_put_u64(arg, bdev->bd_inode->i_size);
> + return compat_put_u64(arg,
> i_size_read(bdev->bd_inode));
> case BLKTRACESETUP32:
> case BLKTRACESTART: /* compatible */
> diff --git a/block/ioctl.c b/block/ioctl.c
> index d724ceb..38aa194 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -125,7 +125,7 @@ static int blk_ioctl_discard(struct block_device
> *bdev, uint64_t start, start >>= 9;
> len >>= 9;
>
> - if (start + len > (bdev->bd_inode->i_size >> 9))
> + if (start + len > (i_size_read(bdev->bd_inode) >> 9))
> return -EINVAL;
> if (secure)
> flags |= BLKDEV_DISCARD_SECURE;
> @@ -307,12 +307,12 @@ int blkdev_ioctl(struct block_device *bdev,
> fmode_t mode, unsigned cmd, ret = blkdev_reread_part(bdev);
> break;
> case BLKGETSIZE:
> - size = bdev->bd_inode->i_size;
> + size = i_size_read(bdev->bd_inode);
> if ((size >> 9) > ~0UL)
> return -EFBIG;
> return put_ulong(arg, size >> 9);
> case BLKGETSIZE64:
> - return put_u64(arg, bdev->bd_inode->i_size);
> + return put_u64(arg, i_size_read(bdev->bd_inode));
> case BLKTRACESTART:
> case BLKTRACESTOP:
> case BLKTRACESETUP:
> diff --git a/drivers/block/drbd/drbd_int.h
> b/drivers/block/drbd/drbd_int.h index 9bdcf43..2637f49 100644
> --- a/drivers/block/drbd/drbd_int.h
> +++ b/drivers/block/drbd/drbd_int.h
> @@ -1874,7 +1874,7 @@ static inline sector_t
> drbd_md_last_sector(struct drbd_backing_dev *bdev) static inline
> sector_t drbd_get_capacity(struct block_device *bdev) {
> /* return bdev ? get_capacity(bdev->bd_disk) : 0; */
> - return bdev ? bdev->bd_inode->i_size >> 9 : 0;
> + return bdev ? i_size_read(bdev->bd_inode) >> 9 : 0;
> }
>
> /**
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 4e957f3..02607b1 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -706,7 +706,7 @@ static struct mdk_personality *find_pers(int
> level, char *clevel) /* return the offset of the super block in
> 512byte sectors */ static inline sector_t calc_dev_sboffset(struct
> block_device *bdev) {
> - sector_t num_sectors = bdev->bd_inode->i_size / 512;
> + sector_t num_sectors = i_size_read(bdev->bd_inode) / 512;
> return MD_NEW_SIZE_SECTORS(num_sectors);
> }
>
> @@ -1386,7 +1386,7 @@ static int super_1_load(mdk_rdev_t *rdev,
> mdk_rdev_t *refdev, int minor_version) */
> switch(minor_version) {
> case 0:
> - sb_start = rdev->bdev->bd_inode->i_size >> 9;
> + sb_start = i_size_read(rdev->bdev->bd_inode) >> 9;
> sb_start -= 8*2;
> sb_start &= ~(sector_t)(4*2-1);
> break;
> @@ -1472,7 +1472,7 @@ static int super_1_load(mdk_rdev_t *rdev,
> mdk_rdev_t *refdev, int minor_version) ret = 0;
> }
> if (minor_version)
> - rdev->sectors = (rdev->bdev->bd_inode->i_size >> 9) -
> + rdev->sectors = (i_size_read(rdev->bdev->bd_inode)
> >> 9) - le64_to_cpu(sb->data_offset);
> else
> rdev->sectors = rdev->sb_start;
> @@ -1680,7 +1680,7 @@ super_1_rdev_size_change(mdk_rdev_t *rdev,
> sector_t num_sectors) return 0; /* component must fit device */
> if (rdev->sb_start < rdev->data_offset) {
> /* minor versions 1 and 2; superblock before data */
> - max_sectors = rdev->bdev->bd_inode->i_size >> 9;
> + max_sectors = i_size_read(rdev->bdev->bd_inode) >> 9;
> max_sectors -= rdev->data_offset;
> if (!num_sectors || num_sectors > max_sectors)
> num_sectors = max_sectors;
> @@ -1690,7 +1690,7 @@ super_1_rdev_size_change(mdk_rdev_t *rdev,
> sector_t num_sectors) } else {
> /* minor version 0; superblock after data */
> sector_t sb_start;
> - sb_start = (rdev->bdev->bd_inode->i_size >> 9) - 8*2;
> + sb_start = (i_size_read(rdev->bdev->bd_inode) >> 9)
> - 8*2; sb_start &= ~(sector_t)(4*2 - 1);
> max_sectors = rdev->sectors + sb_start -
> rdev->sb_start; if (!num_sectors || num_sectors > max_sectors)
> @@ -2584,7 +2584,7 @@ rdev_size_store(mdk_rdev_t *rdev, const char
> *buf, size_t len) if (!sectors)
> return -EBUSY;
> } else if (!sectors)
> - sectors = (rdev->bdev->bd_inode->i_size >>
> 9) -
> + sectors = (i_size_read(rdev->bdev->bd_inode)
> >> 9) - rdev->data_offset;
> }
> if (sectors < my_mddev->dev_sectors)
> @@ -2797,7 +2797,7 @@ static mdk_rdev_t *md_import_device(dev_t
> newdev, int super_format, int super_mi
> kobject_init(&rdev->kobj, &rdev_ktype);
>
> - size = rdev->bdev->bd_inode->i_size >> BLOCK_SIZE_BITS;
> + size = i_size_read(rdev->bdev->bd_inode) >> BLOCK_SIZE_BITS;
> if (!size) {
> printk(KERN_WARNING
> "md: %s has zero or unknown size, marking
> faulty!\n", @@ -5235,7 +5235,7 @@ static int add_new_disk(mddev_t *
> mddev, mdu_disk_info_t *info)
> if (!mddev->persistent) {
> printk(KERN_INFO "md: nonpersistent
> superblock ...\n");
> - rdev->sb_start =
> rdev->bdev->bd_inode->i_size / 512;
> + rdev->sb_start =
> i_size_read(rdev->bdev->bd_inode) / 512; } else
> rdev->sb_start =
> calc_dev_sboffset(rdev->bdev); rdev->sectors = rdev->sb_start;
> @@ -5306,7 +5306,7 @@ static int hot_add_disk(mddev_t * mddev, dev_t
> dev) if (mddev->persistent)
> rdev->sb_start = calc_dev_sboffset(rdev->bdev);
> else
> - rdev->sb_start = rdev->bdev->bd_inode->i_size / 512;
> + rdev->sb_start = i_size_read(rdev->bdev->bd_inode) /
> 512;
> rdev->sectors = rdev->sb_start;
>

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Next message: Andrew Morton: "Re: [PATCH] atomic: add atomic_inc_not_zero_hint()"
Previous message: Andrew Morton: "Re: [PATCH v2] sysfs: device-core: open - close notifier"
In reply to: Mike Snitzer: "[PATCH] block: read i_size with i_size_read()"
Next in thread: Lars Ellenberg: "Re: [Drbd-dev] [PATCH] block: read i_size with i_size_read()"
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