block: add partition resize function to blkpg ioctl
Add a new operation code (BLKPG_RESIZE_PARTITION) to the BLKPG ioctl that allows altering the size of an existing partition, even if it is currently in use. This patch converts hd_struct->nr_sects into sequence counter because One might extend a partition while IO is happening to it and update of nr_sects can be non-atomic on 32bit machines with 64bit sector_t. This can lead to issues like reading inconsistent size of a partition. Sequence counter have been used so that readers don't have to take bdev mutex lock as we call sector_in_part() very frequently. Now all the access to hd_struct->nr_sects should happen using sequence counter read/update helper functions part_nr_sects_read/part_nr_sects_write. There is one exception though, set_capacity()/get_capacity(). I think theoritically race should exist there too but this patch does not modify set_capacity()/get_capacity() due to sheer number of call sites and I am afraid that change might break something. I have left that as a TODO item. We can handle it later if need be. This patch does not introduce any new races as such w.r.t set_capacity()/get_capacity(). v2: Add CONFIG_LBDAF test to UP preempt case as suggested by Phillip. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Phillip Susi <psusi@ubuntu.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Vivek Goyal
Jens Axboe
Родитель
4638a83e86
Коммит
c83f6bf98d
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@ -154,7 +154,7 @@ struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter)
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part = rcu_dereference(ptbl->part[piter->idx]);
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if (!part)
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continue;
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if (!part->nr_sects &&
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if (!part_nr_sects_read(part) &&
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!(piter->flags & DISK_PITER_INCL_EMPTY) &&
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!(piter->flags & DISK_PITER_INCL_EMPTY_PART0 &&
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piter->idx == 0))
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@ -191,7 +191,7 @@ EXPORT_SYMBOL_GPL(disk_part_iter_exit);
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static inline int sector_in_part(struct hd_struct *part, sector_t sector)
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{
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return part->start_sect <= sector &&
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sector < part->start_sect + part->nr_sects;
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sector < part->start_sect + part_nr_sects_read(part);
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}
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/**
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@ -769,8 +769,8 @@ void __init printk_all_partitions(void)
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printk("%s%s %10llu %s %s", is_part0 ? "" : " ",
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bdevt_str(part_devt(part), devt_buf),
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(unsigned long long)part->nr_sects >> 1,
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disk_name(disk, part->partno, name_buf),
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(unsigned long long)part_nr_sects_read(part) >> 1
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, disk_name(disk, part->partno, name_buf),
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uuid_buf);
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if (is_part0) {
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if (disk->driverfs_dev != NULL &&
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@ -862,7 +862,7 @@ static int show_partition(struct seq_file *seqf, void *v)
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while ((part = disk_part_iter_next(&piter)))
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seq_printf(seqf, "%4d %7d %10llu %s\n",
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MAJOR(part_devt(part)), MINOR(part_devt(part)),
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(unsigned long long)part->nr_sects >> 1,
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(unsigned long long)part_nr_sects_read(part) >> 1,
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disk_name(sgp, part->partno, buf));
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disk_part_iter_exit(&piter);
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@ -1268,6 +1268,16 @@ struct gendisk *alloc_disk_node(int minors, int node_id)
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}
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disk->part_tbl->part[0] = &disk->part0;
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/*
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* set_capacity() and get_capacity() currently don't use
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* seqcounter to read/update the part0->nr_sects. Still init
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* the counter as we can read the sectors in IO submission
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* patch using seqence counters.
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*
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* TODO: Ideally set_capacity() and get_capacity() should be
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* converted to make use of bd_mutex and sequence counters.
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*/
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seqcount_init(&disk->part0.nr_sects_seq);
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hd_ref_init(&disk->part0);
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disk->minors = minors;
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@ -13,7 +13,7 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
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{
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struct block_device *bdevp;
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struct gendisk *disk;
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struct hd_struct *part;
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struct hd_struct *part, *lpart;
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struct blkpg_ioctl_arg a;
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struct blkpg_partition p;
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struct disk_part_iter piter;
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@ -36,8 +36,8 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
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case BLKPG_ADD_PARTITION:
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start = p.start >> 9;
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length = p.length >> 9;
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/* check for fit in a hd_struct */
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if (sizeof(sector_t) == sizeof(long) &&
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/* check for fit in a hd_struct */
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if (sizeof(sector_t) == sizeof(long) &&
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sizeof(long long) > sizeof(long)) {
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long pstart = start, plength = length;
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if (pstart != start || plength != length
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@ -91,6 +91,59 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
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mutex_unlock(&bdevp->bd_mutex);
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bdput(bdevp);
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return 0;
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case BLKPG_RESIZE_PARTITION:
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start = p.start >> 9;
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/* new length of partition in bytes */
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length = p.length >> 9;
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/* check for fit in a hd_struct */
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if (sizeof(sector_t) == sizeof(long) &&
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sizeof(long long) > sizeof(long)) {
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long pstart = start, plength = length;
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if (pstart != start || plength != length
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|| pstart < 0 || plength < 0)
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return -EINVAL;
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}
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part = disk_get_part(disk, partno);
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if (!part)
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return -ENXIO;
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bdevp = bdget(part_devt(part));
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if (!bdevp) {
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disk_put_part(part);
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return -ENOMEM;
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}
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mutex_lock(&bdevp->bd_mutex);
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mutex_lock_nested(&bdev->bd_mutex, 1);
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if (start != part->start_sect) {
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mutex_unlock(&bdevp->bd_mutex);
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mutex_unlock(&bdev->bd_mutex);
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bdput(bdevp);
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disk_put_part(part);
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return -EINVAL;
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}
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/* overlap? */
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disk_part_iter_init(&piter, disk,
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DISK_PITER_INCL_EMPTY);
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while ((lpart = disk_part_iter_next(&piter))) {
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if (lpart->partno != partno &&
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!(start + length <= lpart->start_sect ||
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start >= lpart->start_sect + lpart->nr_sects)
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) {
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disk_part_iter_exit(&piter);
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mutex_unlock(&bdevp->bd_mutex);
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mutex_unlock(&bdev->bd_mutex);
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bdput(bdevp);
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disk_put_part(part);
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return -EBUSY;
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}
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}
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disk_part_iter_exit(&piter);
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part_nr_sects_write(part, (sector_t)length);
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i_size_write(bdevp->bd_inode, p.length);
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mutex_unlock(&bdevp->bd_mutex);
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mutex_unlock(&bdev->bd_mutex);
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bdput(bdevp);
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disk_put_part(part);
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return 0;
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default:
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return -EINVAL;
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@ -84,7 +84,7 @@ ssize_t part_size_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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struct hd_struct *p = dev_to_part(dev);
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return sprintf(buf, "%llu\n",(unsigned long long)p->nr_sects);
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return sprintf(buf, "%llu\n",(unsigned long long)part_nr_sects_read(p));
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}
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static ssize_t part_ro_show(struct device *dev,
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@ -294,6 +294,8 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
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err = -ENOMEM;
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goto out_free;
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}
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seqcount_init(&p->nr_sects_seq);
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pdev = part_to_dev(p);
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p->start_sect = start;
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@ -40,6 +40,7 @@ struct blkpg_ioctl_arg {
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/* The subfunctions (for the op field) */
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#define BLKPG_ADD_PARTITION 1
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#define BLKPG_DEL_PARTITION 2
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#define BLKPG_RESIZE_PARTITION 3
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/* Sizes of name fields. Unused at present. */
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#define BLKPG_DEVNAMELTH 64
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@ -98,7 +98,13 @@ struct partition_meta_info {
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struct hd_struct {
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sector_t start_sect;
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/*
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* nr_sects is protected by sequence counter. One might extend a
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* partition while IO is happening to it and update of nr_sects
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* can be non-atomic on 32bit machines with 64bit sector_t.
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*/
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sector_t nr_sects;
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seqcount_t nr_sects_seq;
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sector_t alignment_offset;
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unsigned int discard_alignment;
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struct device __dev;
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@ -648,6 +654,57 @@ static inline void hd_struct_put(struct hd_struct *part)
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__delete_partition(part);
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}
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/*
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* Any access of part->nr_sects which is not protected by partition
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* bd_mutex or gendisk bdev bd_mutex, should be done using this
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* accessor function.
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*
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* Code written along the lines of i_size_read() and i_size_write().
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* CONFIG_PREEMPT case optimizes the case of UP kernel with preemption
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* on.
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*/
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static inline sector_t part_nr_sects_read(struct hd_struct *part)
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{
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#if BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_SMP)
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sector_t nr_sects;
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unsigned seq;
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do {
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seq = read_seqcount_begin(&part->nr_sects_seq);
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nr_sects = part->nr_sects;
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} while (read_seqcount_retry(&part->nr_sects_seq, seq));
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return nr_sects;
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#elif BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_PREEMPT)
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sector_t nr_sects;
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preempt_disable();
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nr_sects = part->nr_sects;
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preempt_enable();
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return nr_sects;
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#else
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return part->nr_sects;
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#endif
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}
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/*
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* Should be called with mutex lock held (typically bd_mutex) of partition
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* to provide mutual exlusion among writers otherwise seqcount might be
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* left in wrong state leaving the readers spinning infinitely.
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*/
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static inline void part_nr_sects_write(struct hd_struct *part, sector_t size)
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{
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#if BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_SMP)
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write_seqcount_begin(&part->nr_sects_seq);
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part->nr_sects = size;
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write_seqcount_end(&part->nr_sects_seq);
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#elif BITS_PER_LONG==32 && defined(CONFIG_LBDAF) && defined(CONFIG_PREEMPT)
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preempt_disable();
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part->nr_sects = size;
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preempt_enable();
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#else
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part->nr_sects = size;
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#endif
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}
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#else /* CONFIG_BLOCK */
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static inline void printk_all_partitions(void) { }
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