Re: [PATCH 1/2] Add partition resize function to BLKPG ioctl

From: Phillip Susi
Date: Thu Dec 08 2011 - 21:53:21 EST

On 12/08/2011 11:28 AM, Vivek Goyal wrote:
> I thought I have found couple of places where we don't take mutex. For
> example.

I merged your seq changes into my patch. How does this look?


From 8dbca9e824dd18eeb44079717234db0e853f8478 Mon Sep 17 00:00:00 2001
From: Phillip Susi <psusi@xxxxxxxxxx>
Date: Wed, 30 Nov 2011 22:05:24 -0500
Subject: [PATCH 1/3] Add partition resize function to BLKPG ioctl

Add a new operation code ( BLKPG_RES_PARTITION ) to the
BLKPG ioctl that allows altering the size of an existing
partition, even if it is currently in use.
---
block/genhd.c | 10 ++++----
block/ioctl.c | 51 +++++++++++++++++++++++++++++++++++++-
fs/partitions/check.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++-
include/linux/blkpg.h | 1 +
include/linux/genhd.h | 7 +++++
5 files changed, 126 insertions(+), 8 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 02e9fca..b34fb90 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -154,7 +154,7 @@ struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter)
part = rcu_dereference(ptbl->part[piter->idx]);
if (!part)
continue;
- if (!part->nr_sects &&
+ if (!part_nr_sects_read(part) &&
!(piter->flags & DISK_PITER_INCL_EMPTY) &&
!(piter->flags & DISK_PITER_INCL_EMPTY_PART0 &&
piter->idx == 0))
@@ -191,7 +191,7 @@ EXPORT_SYMBOL_GPL(disk_part_iter_exit);
static inline int sector_in_part(struct hd_struct *part, sector_t sector)
{
return part->start_sect <= sector &&
- sector < part->start_sect + part->nr_sects;
+ sector < part->start_sect + part_nr_sects_read(part);
}

/**
@@ -766,8 +766,8 @@ void __init printk_all_partitions(void)

printk("%s%s %10llu %s %s", is_part0 ? "" : " ",
bdevt_str(part_devt(part), devt_buf),
- (unsigned long long)part->nr_sects >> 1,
- disk_name(disk, part->partno, name_buf), uuid);
+ (unsigned long long)part_nr_sects_read(part) >> 1
+ , disk_name(disk, part->partno, name_buf), uuid);
if (is_part0) {
if (disk->driverfs_dev != NULL &&
disk->driverfs_dev->driver != NULL)
@@ -858,7 +858,7 @@ static int show_partition(struct seq_file *seqf, void *v)
while ((part = disk_part_iter_next(&piter)))
seq_printf(seqf, "%4d %7d %10llu %s\n",
MAJOR(part_devt(part)), MINOR(part_devt(part)),
- (unsigned long long)part->nr_sects >> 1,
+ (unsigned long long)part_nr_sects_read(part) >> 1,
disk_name(sgp, part->partno, buf));
disk_part_iter_exit(&piter);

diff --git a/block/ioctl.c b/block/ioctl.c
index ca939fc..f97e6a4 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -36,8 +36,8 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
case BLKPG_ADD_PARTITION:
start = p.start >> 9;
length = p.length >> 9;
- /* check for fit in a hd_struct */
- if (sizeof(sector_t) == sizeof(long) &&
+ /* check for fit in a hd_struct */
+ if (sizeof(sector_t) == sizeof(long) &&
sizeof(long long) > sizeof(long)) {
long pstart = start, plength = length;
if (pstart != start || plength != length
@@ -92,6 +92,53 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
bdput(bdevp);

return 0;
+ case BLKPG_RES_PARTITION:
+ start = p.start >> 9;
+ length = p.length >> 9;
+ /* check for fit in a hd_struct */
+ if (sizeof(sector_t) == sizeof(long) &&
+ sizeof(long long) > sizeof(long)) {
+ long pstart = start, plength = length;
+ if (pstart != start || plength != length
+ || pstart < 0 || plength < 0)
+ return -EINVAL;
+ }
+
+ mutex_lock(&bdev->bd_mutex);
+
+ /* overlap? */
+ disk_part_iter_init(&piter, disk,
+ DISK_PITER_INCL_EMPTY);
+ while ((part = disk_part_iter_next(&piter))) {
+ if (part->partno != partno && !(start + length <= part->start_sect ||
+ start >= part->start_sect + part->nr_sects)) {
+ disk_part_iter_exit(&piter);
+ mutex_unlock(&bdev->bd_mutex);
+ return -EBUSY;
+ }
+ }
+ disk_part_iter_exit(&piter);
+ part = disk_get_part(disk, partno);
+ if (!part)
+ {
+ mutex_unlock(&bdev->bd_mutex);
+ return -ENXIO;
+ }
+ if (start != part->start_sect)
+ {
+ mutex_unlock(&bdev->bd_mutex);
+ disk_put_part(part);
+ return -EINVAL;
+ }
+ part->nr_sects = length;
+ bdevp = bdget(part_devt(part));
+ mutex_lock(&bdevp->bd_mutex);
+ i_size_write(bdevp->bd_inode, p.length);
+ mutex_unlock(&bdevp->bd_mutex);
+ bdput(bdevp);
+ disk_put_part(part);
+ mutex_unlock(&bdev->bd_mutex);
+ return 0;
default:
return -EINVAL;
}
diff --git a/fs/partitions/check.c b/fs/partitions/check.c
index e3c63d1..090ee1a 100644
--- a/fs/partitions/check.c
+++ b/fs/partitions/check.c
@@ -234,7 +234,7 @@ ssize_t part_size_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct hd_struct *p = dev_to_part(dev);
- return sprintf(buf, "%llu\n",(unsigned long long)p->nr_sects);
+ return sprintf(buf, "%llu\n",(unsigned long long)part_nr_sects_read(p));
}

static ssize_t part_ro_show(struct device *dev,
@@ -408,6 +408,69 @@ void delete_partition(struct gendisk *disk, int partno)
hd_struct_put(part);
}

+#if BITS_PER_LONG == 32 && defined(CONFIG_LBDAF)
+static inline void part_nr_sects_write_begin(struct seqcount_t *seq)
+{
+ write_seqcount_begin(&seq);
+}
+
+static inline void part_nr_sects_write_end(struct seqcount_t *seq)
+{
+ write_seqcount_end(&seq);
+}
+
+/*
+ * Any access of part->nr_sects which is not protected by partition
+ * bd_mutex or gendisk bdev bd_mutex, hould be done using this accessor
+ * function.
+ */
+sector_t part_nr_sects_read(struct hd_struct *part)
+{
+ sector_t nr_sects;
+ unsigned seq;
+
+ do {
+ seq = read_seqcount_begin(&part->seq);
+ nr_sects = part->nr_sects;
+ } while (read_seqcount_retry(&part->seq, seq));
+
+ return nr_sects;
+}
+#else
+static inline void part_nr_sects_write_begin(seqcount_t *seq) {}
+static inline void part_nr_sects_write_end(seqcount_t *seq) {}
+sector_t part_nr_sects_read(struct hd_struct *part)
+{
+ return part->nr_sects;
+}
+#endif
+
+int extend_partition(struct gendisk *disk, int partno, sector_t size)
+{
+ struct disk_part_tbl *ptbl = disk->part_tbl;
+ struct hd_struct *part;
+ unsigned long flags;
+
+ if (partno >= ptbl->len)
+ return 1;
+
+ part = ptbl->part[partno];
+ if (!part)
+ return 1;
+
+ /*
+ * It is called with mutex held for writer mutual exclusion. Disabling
+ * interrupts to protect against a reader in interrupt/softirq
+ * context. Is it not needed?
+ */
+ local_irq_save(flags);
+ part_nr_sects_write_begin(&part->seq);
+ part->nr_sects += size;
+ part_nr_sects_write_end(&part->seq);
+ local_irq_restore(flags);
+ return 0;
+}
+
static ssize_t whole_disk_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
diff --git a/include/linux/blkpg.h b/include/linux/blkpg.h
index faf8a45..103da38 100644
--- a/include/linux/blkpg.h
+++ b/include/linux/blkpg.h
@@ -40,6 +40,7 @@ struct blkpg_ioctl_arg {
/* The subfunctions (for the op field) */
#define BLKPG_ADD_PARTITION 1
#define BLKPG_DEL_PARTITION 2
+#define BLKPG_RES_PARTITION 3

/* Sizes of name fields. Unused at present. */
#define BLKPG_DEVNAMELTH 64
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 6d18f35..a55ce2c 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -98,7 +98,13 @@ struct partition_meta_info {

struct hd_struct {
sector_t start_sect;
+ /*
+ * nr_sects is protected by sequence counter. 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.
+ */
sector_t nr_sects;
+ seqcount_t seq;
sector_t alignment_offset;
unsigned int discard_alignment;
struct device __dev;
@@ -604,6 +610,7 @@ extern struct hd_struct * __must_check add_partition(struct gendisk *disk,
extern void __delete_partition(struct hd_struct *);
extern void delete_partition(struct gendisk *, int);
extern void printk_all_partitions(void);
+extern sector_t part_nr_sects_read(struct hd_struct *part);

extern struct gendisk *alloc_disk_node(int minors, int node_id);
extern struct gendisk *alloc_disk(int minors);
--
1.7.5.4

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