linux/block/partition-generic.c
Yufen Yu 94a2c3a32b block: use rcu_work instead of call_rcu to avoid sleep in softirq
We recently got a stack by syzkaller like this:

BUG: sleeping function called from invalid context at mm/slab.h:361
in_atomic(): 1, irqs_disabled(): 0, pid: 6644, name: blkid
INFO: lockdep is turned off.
CPU: 1 PID: 6644 Comm: blkid Not tainted 4.4.163-514.55.6.9.x86_64+ #76
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
 0000000000000000 5ba6a6b879e50c00 ffff8801f6b07b10 ffffffff81cb2194
 0000000041b58ab3 ffffffff833c7745 ffffffff81cb2080 5ba6a6b879e50c00
 0000000000000000 0000000000000001 0000000000000004 0000000000000000
Call Trace:
 <IRQ>  [<ffffffff81cb2194>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ>  [<ffffffff81cb2194>] dump_stack+0x114/0x1a0 lib/dump_stack.c:51
 [<ffffffff8129a981>] ___might_sleep+0x291/0x490 kernel/sched/core.c:7675
 [<ffffffff8129ac33>] __might_sleep+0xb3/0x270 kernel/sched/core.c:7637
 [<ffffffff81794c13>] slab_pre_alloc_hook mm/slab.h:361 [inline]
 [<ffffffff81794c13>] slab_alloc_node mm/slub.c:2610 [inline]
 [<ffffffff81794c13>] slab_alloc mm/slub.c:2692 [inline]
 [<ffffffff81794c13>] kmem_cache_alloc_trace+0x2c3/0x5c0 mm/slub.c:2709
 [<ffffffff81cbe9a7>] kmalloc include/linux/slab.h:479 [inline]
 [<ffffffff81cbe9a7>] kzalloc include/linux/slab.h:623 [inline]
 [<ffffffff81cbe9a7>] kobject_uevent_env+0x2c7/0x1150 lib/kobject_uevent.c:227
 [<ffffffff81cbf84f>] kobject_uevent+0x1f/0x30 lib/kobject_uevent.c:374
 [<ffffffff81cbb5b9>] kobject_cleanup lib/kobject.c:633 [inline]
 [<ffffffff81cbb5b9>] kobject_release+0x229/0x440 lib/kobject.c:675
 [<ffffffff81cbb0a2>] kref_sub include/linux/kref.h:73 [inline]
 [<ffffffff81cbb0a2>] kref_put include/linux/kref.h:98 [inline]
 [<ffffffff81cbb0a2>] kobject_put+0x72/0xd0 lib/kobject.c:692
 [<ffffffff8216f095>] put_device+0x25/0x30 drivers/base/core.c:1237
 [<ffffffff81c4cc34>] delete_partition_rcu_cb+0x1d4/0x2f0 block/partition-generic.c:232
 [<ffffffff813c08bc>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff813c08bc>] rcu_do_batch kernel/rcu/tree.c:2705 [inline]
 [<ffffffff813c08bc>] invoke_rcu_callbacks kernel/rcu/tree.c:2973 [inline]
 [<ffffffff813c08bc>] __rcu_process_callbacks kernel/rcu/tree.c:2940 [inline]
 [<ffffffff813c08bc>] rcu_process_callbacks+0x59c/0x1c70 kernel/rcu/tree.c:2957
 [<ffffffff8120f509>] __do_softirq+0x299/0xe20 kernel/softirq.c:273
 [<ffffffff81210496>] invoke_softirq kernel/softirq.c:350 [inline]
 [<ffffffff81210496>] irq_exit+0x216/0x2c0 kernel/softirq.c:391
 [<ffffffff82c2cd7b>] exiting_irq arch/x86/include/asm/apic.h:652 [inline]
 [<ffffffff82c2cd7b>] smp_apic_timer_interrupt+0x8b/0xc0 arch/x86/kernel/apic/apic.c:926
 [<ffffffff82c2bc25>] apic_timer_interrupt+0xa5/0xb0 arch/x86/entry/entry_64.S:746
 <EOI>  [<ffffffff814cbf40>] ? audit_kill_trees+0x180/0x180
 [<ffffffff8187d2f7>] fd_install+0x57/0x80 fs/file.c:626
 [<ffffffff8180989e>] do_sys_open+0x45e/0x550 fs/open.c:1043
 [<ffffffff818099c2>] SYSC_open fs/open.c:1055 [inline]
 [<ffffffff818099c2>] SyS_open+0x32/0x40 fs/open.c:1050
 [<ffffffff82c299e1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

In softirq context, we call rcu callback function delete_partition_rcu_cb(),
which may allocate memory by kzalloc with GFP_KERNEL flag. If the
allocation cannot be satisfied, it may sleep. However, That is not allowed
in softirq contex.

Although we found this problem on linux 4.4, the latest kernel version
seems to have this problem as well. And it is very similar to the
previous one:
	https://lkml.org/lkml/2018/7/9/391

Fix it by using RCU workqueue, which allows sleep.

Reviewed-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-11-28 09:08:27 -07:00

678 lines
17 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Code extracted from drivers/block/genhd.c
* Copyright (C) 1991-1998 Linus Torvalds
* Re-organised Feb 1998 Russell King
*
* We now have independent partition support from the
* block drivers, which allows all the partition code to
* be grouped in one location, and it to be mostly self
* contained.
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/kmod.h>
#include <linux/ctype.h>
#include <linux/genhd.h>
#include <linux/blktrace_api.h>
#include "partitions/check.h"
#ifdef CONFIG_BLK_DEV_MD
extern void md_autodetect_dev(dev_t dev);
#endif
/*
* disk_name() is used by partition check code and the genhd driver.
* It formats the devicename of the indicated disk into
* the supplied buffer (of size at least 32), and returns
* a pointer to that same buffer (for convenience).
*/
char *disk_name(struct gendisk *hd, int partno, char *buf)
{
if (!partno)
snprintf(buf, BDEVNAME_SIZE, "%s", hd->disk_name);
else if (isdigit(hd->disk_name[strlen(hd->disk_name)-1]))
snprintf(buf, BDEVNAME_SIZE, "%sp%d", hd->disk_name, partno);
else
snprintf(buf, BDEVNAME_SIZE, "%s%d", hd->disk_name, partno);
return buf;
}
const char *bdevname(struct block_device *bdev, char *buf)
{
return disk_name(bdev->bd_disk, bdev->bd_part->partno, buf);
}
EXPORT_SYMBOL(bdevname);
const char *bio_devname(struct bio *bio, char *buf)
{
return disk_name(bio->bi_disk, bio->bi_partno, buf);
}
EXPORT_SYMBOL(bio_devname);
/*
* There's very little reason to use this, you should really
* have a struct block_device just about everywhere and use
* bdevname() instead.
*/
const char *__bdevname(dev_t dev, char *buffer)
{
scnprintf(buffer, BDEVNAME_SIZE, "unknown-block(%u,%u)",
MAJOR(dev), MINOR(dev));
return buffer;
}
EXPORT_SYMBOL(__bdevname);
static ssize_t part_partition_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct hd_struct *p = dev_to_part(dev);
return sprintf(buf, "%d\n", p->partno);
}
static ssize_t part_start_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->start_sect);
}
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)part_nr_sects_read(p));
}
static ssize_t part_ro_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct hd_struct *p = dev_to_part(dev);
return sprintf(buf, "%d\n", p->policy ? 1 : 0);
}
static ssize_t part_alignment_offset_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->alignment_offset);
}
static ssize_t part_discard_alignment_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct hd_struct *p = dev_to_part(dev);
return sprintf(buf, "%u\n", p->discard_alignment);
}
ssize_t part_stat_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct hd_struct *p = dev_to_part(dev);
struct request_queue *q = part_to_disk(p)->queue;
unsigned int inflight[2];
int cpu;
cpu = part_stat_lock();
part_round_stats(q, cpu, p);
part_stat_unlock();
part_in_flight(q, p, inflight);
return sprintf(buf,
"%8lu %8lu %8llu %8u "
"%8lu %8lu %8llu %8u "
"%8u %8u %8u "
"%8lu %8lu %8llu %8u"
"\n",
part_stat_read(p, ios[STAT_READ]),
part_stat_read(p, merges[STAT_READ]),
(unsigned long long)part_stat_read(p, sectors[STAT_READ]),
(unsigned int)part_stat_read_msecs(p, STAT_READ),
part_stat_read(p, ios[STAT_WRITE]),
part_stat_read(p, merges[STAT_WRITE]),
(unsigned long long)part_stat_read(p, sectors[STAT_WRITE]),
(unsigned int)part_stat_read_msecs(p, STAT_WRITE),
inflight[0],
jiffies_to_msecs(part_stat_read(p, io_ticks)),
jiffies_to_msecs(part_stat_read(p, time_in_queue)),
part_stat_read(p, ios[STAT_DISCARD]),
part_stat_read(p, merges[STAT_DISCARD]),
(unsigned long long)part_stat_read(p, sectors[STAT_DISCARD]),
(unsigned int)part_stat_read_msecs(p, STAT_DISCARD));
}
ssize_t part_inflight_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
struct hd_struct *p = dev_to_part(dev);
struct request_queue *q = part_to_disk(p)->queue;
unsigned int inflight[2];
part_in_flight_rw(q, p, inflight);
return sprintf(buf, "%8u %8u\n", inflight[0], inflight[1]);
}
#ifdef CONFIG_FAIL_MAKE_REQUEST
ssize_t part_fail_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct hd_struct *p = dev_to_part(dev);
return sprintf(buf, "%d\n", p->make_it_fail);
}
ssize_t part_fail_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
struct hd_struct *p = dev_to_part(dev);
int i;
if (count > 0 && sscanf(buf, "%d", &i) > 0)
p->make_it_fail = (i == 0) ? 0 : 1;
return count;
}
#endif
static DEVICE_ATTR(partition, 0444, part_partition_show, NULL);
static DEVICE_ATTR(start, 0444, part_start_show, NULL);
static DEVICE_ATTR(size, 0444, part_size_show, NULL);
static DEVICE_ATTR(ro, 0444, part_ro_show, NULL);
static DEVICE_ATTR(alignment_offset, 0444, part_alignment_offset_show, NULL);
static DEVICE_ATTR(discard_alignment, 0444, part_discard_alignment_show, NULL);
static DEVICE_ATTR(stat, 0444, part_stat_show, NULL);
static DEVICE_ATTR(inflight, 0444, part_inflight_show, NULL);
#ifdef CONFIG_FAIL_MAKE_REQUEST
static struct device_attribute dev_attr_fail =
__ATTR(make-it-fail, 0644, part_fail_show, part_fail_store);
#endif
static struct attribute *part_attrs[] = {
&dev_attr_partition.attr,
&dev_attr_start.attr,
&dev_attr_size.attr,
&dev_attr_ro.attr,
&dev_attr_alignment_offset.attr,
&dev_attr_discard_alignment.attr,
&dev_attr_stat.attr,
&dev_attr_inflight.attr,
#ifdef CONFIG_FAIL_MAKE_REQUEST
&dev_attr_fail.attr,
#endif
NULL
};
static struct attribute_group part_attr_group = {
.attrs = part_attrs,
};
static const struct attribute_group *part_attr_groups[] = {
&part_attr_group,
#ifdef CONFIG_BLK_DEV_IO_TRACE
&blk_trace_attr_group,
#endif
NULL
};
static void part_release(struct device *dev)
{
struct hd_struct *p = dev_to_part(dev);
blk_free_devt(dev->devt);
hd_free_part(p);
kfree(p);
}
static int part_uevent(struct device *dev, struct kobj_uevent_env *env)
{
struct hd_struct *part = dev_to_part(dev);
add_uevent_var(env, "PARTN=%u", part->partno);
if (part->info && part->info->volname[0])
add_uevent_var(env, "PARTNAME=%s", part->info->volname);
return 0;
}
struct device_type part_type = {
.name = "partition",
.groups = part_attr_groups,
.release = part_release,
.uevent = part_uevent,
};
static void delete_partition_work_fn(struct work_struct *work)
{
struct hd_struct *part = container_of(to_rcu_work(work), struct hd_struct,
rcu_work);
part->start_sect = 0;
part->nr_sects = 0;
part_stat_set_all(part, 0);
put_device(part_to_dev(part));
}
void __delete_partition(struct percpu_ref *ref)
{
struct hd_struct *part = container_of(ref, struct hd_struct, ref);
INIT_RCU_WORK(&part->rcu_work, delete_partition_work_fn);
queue_rcu_work(system_wq, &part->rcu_work);
}
/*
* Must be called either with bd_mutex held, before a disk can be opened or
* after all disk users are gone.
*/
void delete_partition(struct gendisk *disk, int partno)
{
struct disk_part_tbl *ptbl =
rcu_dereference_protected(disk->part_tbl, 1);
struct hd_struct *part;
if (partno >= ptbl->len)
return;
part = rcu_dereference_protected(ptbl->part[partno], 1);
if (!part)
return;
rcu_assign_pointer(ptbl->part[partno], NULL);
rcu_assign_pointer(ptbl->last_lookup, NULL);
kobject_put(part->holder_dir);
device_del(part_to_dev(part));
hd_struct_kill(part);
}
static ssize_t whole_disk_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
return 0;
}
static DEVICE_ATTR(whole_disk, 0444, whole_disk_show, NULL);
/*
* Must be called either with bd_mutex held, before a disk can be opened or
* after all disk users are gone.
*/
struct hd_struct *add_partition(struct gendisk *disk, int partno,
sector_t start, sector_t len, int flags,
struct partition_meta_info *info)
{
struct hd_struct *p;
dev_t devt = MKDEV(0, 0);
struct device *ddev = disk_to_dev(disk);
struct device *pdev;
struct disk_part_tbl *ptbl;
const char *dname;
int err;
err = disk_expand_part_tbl(disk, partno);
if (err)
return ERR_PTR(err);
ptbl = rcu_dereference_protected(disk->part_tbl, 1);
if (ptbl->part[partno])
return ERR_PTR(-EBUSY);
p = kzalloc(sizeof(*p), GFP_KERNEL);
if (!p)
return ERR_PTR(-EBUSY);
if (!init_part_stats(p)) {
err = -ENOMEM;
goto out_free;
}
seqcount_init(&p->nr_sects_seq);
pdev = part_to_dev(p);
p->start_sect = start;
p->alignment_offset =
queue_limit_alignment_offset(&disk->queue->limits, start);
p->discard_alignment =
queue_limit_discard_alignment(&disk->queue->limits, start);
p->nr_sects = len;
p->partno = partno;
p->policy = get_disk_ro(disk);
if (info) {
struct partition_meta_info *pinfo = alloc_part_info(disk);
if (!pinfo) {
err = -ENOMEM;
goto out_free_stats;
}
memcpy(pinfo, info, sizeof(*info));
p->info = pinfo;
}
dname = dev_name(ddev);
if (isdigit(dname[strlen(dname) - 1]))
dev_set_name(pdev, "%sp%d", dname, partno);
else
dev_set_name(pdev, "%s%d", dname, partno);
device_initialize(pdev);
pdev->class = &block_class;
pdev->type = &part_type;
pdev->parent = ddev;
err = blk_alloc_devt(p, &devt);
if (err)
goto out_free_info;
pdev->devt = devt;
/* delay uevent until 'holders' subdir is created */
dev_set_uevent_suppress(pdev, 1);
err = device_add(pdev);
if (err)
goto out_put;
err = -ENOMEM;
p->holder_dir = kobject_create_and_add("holders", &pdev->kobj);
if (!p->holder_dir)
goto out_del;
dev_set_uevent_suppress(pdev, 0);
if (flags & ADDPART_FLAG_WHOLEDISK) {
err = device_create_file(pdev, &dev_attr_whole_disk);
if (err)
goto out_del;
}
err = hd_ref_init(p);
if (err) {
if (flags & ADDPART_FLAG_WHOLEDISK)
goto out_remove_file;
goto out_del;
}
/* everything is up and running, commence */
rcu_assign_pointer(ptbl->part[partno], p);
/* suppress uevent if the disk suppresses it */
if (!dev_get_uevent_suppress(ddev))
kobject_uevent(&pdev->kobj, KOBJ_ADD);
return p;
out_free_info:
free_part_info(p);
out_free_stats:
free_part_stats(p);
out_free:
kfree(p);
return ERR_PTR(err);
out_remove_file:
device_remove_file(pdev, &dev_attr_whole_disk);
out_del:
kobject_put(p->holder_dir);
device_del(pdev);
out_put:
put_device(pdev);
return ERR_PTR(err);
}
static bool disk_unlock_native_capacity(struct gendisk *disk)
{
const struct block_device_operations *bdops = disk->fops;
if (bdops->unlock_native_capacity &&
!(disk->flags & GENHD_FL_NATIVE_CAPACITY)) {
printk(KERN_CONT "enabling native capacity\n");
bdops->unlock_native_capacity(disk);
disk->flags |= GENHD_FL_NATIVE_CAPACITY;
return true;
} else {
printk(KERN_CONT "truncated\n");
return false;
}
}
static int drop_partitions(struct gendisk *disk, struct block_device *bdev)
{
struct disk_part_iter piter;
struct hd_struct *part;
int res;
if (bdev->bd_part_count || bdev->bd_super)
return -EBUSY;
res = invalidate_partition(disk, 0);
if (res)
return res;
disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY);
while ((part = disk_part_iter_next(&piter)))
delete_partition(disk, part->partno);
disk_part_iter_exit(&piter);
return 0;
}
static bool part_zone_aligned(struct gendisk *disk,
struct block_device *bdev,
sector_t from, sector_t size)
{
unsigned int zone_sectors = bdev_zone_sectors(bdev);
/*
* If this function is called, then the disk is a zoned block device
* (host-aware or host-managed). This can be detected even if the
* zoned block device support is disabled (CONFIG_BLK_DEV_ZONED not
* set). In this case, however, only host-aware devices will be seen
* as a block device is not created for host-managed devices. Without
* zoned block device support, host-aware drives can still be used as
* regular block devices (no zone operation) and their zone size will
* be reported as 0. Allow this case.
*/
if (!zone_sectors)
return true;
/*
* Check partition start and size alignement. If the drive has a
* smaller last runt zone, ignore it and allow the partition to
* use it. Check the zone size too: it should be a power of 2 number
* of sectors.
*/
if (WARN_ON_ONCE(!is_power_of_2(zone_sectors))) {
u32 rem;
div_u64_rem(from, zone_sectors, &rem);
if (rem)
return false;
if ((from + size) < get_capacity(disk)) {
div_u64_rem(size, zone_sectors, &rem);
if (rem)
return false;
}
} else {
if (from & (zone_sectors - 1))
return false;
if ((from + size) < get_capacity(disk) &&
(size & (zone_sectors - 1)))
return false;
}
return true;
}
int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
{
struct parsed_partitions *state = NULL;
struct hd_struct *part;
int p, highest, res;
rescan:
if (state && !IS_ERR(state)) {
free_partitions(state);
state = NULL;
}
res = drop_partitions(disk, bdev);
if (res)
return res;
if (disk->fops->revalidate_disk)
disk->fops->revalidate_disk(disk);
check_disk_size_change(disk, bdev, true);
bdev->bd_invalidated = 0;
if (!get_capacity(disk) || !(state = check_partition(disk, bdev)))
return 0;
if (IS_ERR(state)) {
/*
* I/O error reading the partition table. If any
* partition code tried to read beyond EOD, retry
* after unlocking native capacity.
*/
if (PTR_ERR(state) == -ENOSPC) {
printk(KERN_WARNING "%s: partition table beyond EOD, ",
disk->disk_name);
if (disk_unlock_native_capacity(disk))
goto rescan;
}
return -EIO;
}
/*
* If any partition code tried to read beyond EOD, try
* unlocking native capacity even if partition table is
* successfully read as we could be missing some partitions.
*/
if (state->access_beyond_eod) {
printk(KERN_WARNING
"%s: partition table partially beyond EOD, ",
disk->disk_name);
if (disk_unlock_native_capacity(disk))
goto rescan;
}
/* tell userspace that the media / partition table may have changed */
kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
/* Detect the highest partition number and preallocate
* disk->part_tbl. This is an optimization and not strictly
* necessary.
*/
for (p = 1, highest = 0; p < state->limit; p++)
if (state->parts[p].size)
highest = p;
disk_expand_part_tbl(disk, highest);
/* add partitions */
for (p = 1; p < state->limit; p++) {
sector_t size, from;
size = state->parts[p].size;
if (!size)
continue;
from = state->parts[p].from;
if (from >= get_capacity(disk)) {
printk(KERN_WARNING
"%s: p%d start %llu is beyond EOD, ",
disk->disk_name, p, (unsigned long long) from);
if (disk_unlock_native_capacity(disk))
goto rescan;
continue;
}
if (from + size > get_capacity(disk)) {
printk(KERN_WARNING
"%s: p%d size %llu extends beyond EOD, ",
disk->disk_name, p, (unsigned long long) size);
if (disk_unlock_native_capacity(disk)) {
/* free state and restart */
goto rescan;
} else {
/*
* we can not ignore partitions of broken tables
* created by for example camera firmware, but
* we limit them to the end of the disk to avoid
* creating invalid block devices
*/
size = get_capacity(disk) - from;
}
}
/*
* On a zoned block device, partitions should be aligned on the
* device zone size (i.e. zone boundary crossing not allowed).
* Otherwise, resetting the write pointer of the last zone of
* one partition may impact the following partition.
*/
if (bdev_is_zoned(bdev) &&
!part_zone_aligned(disk, bdev, from, size)) {
printk(KERN_WARNING
"%s: p%d start %llu+%llu is not zone aligned\n",
disk->disk_name, p, (unsigned long long) from,
(unsigned long long) size);
continue;
}
part = add_partition(disk, p, from, size,
state->parts[p].flags,
&state->parts[p].info);
if (IS_ERR(part)) {
printk(KERN_ERR " %s: p%d could not be added: %ld\n",
disk->disk_name, p, -PTR_ERR(part));
continue;
}
#ifdef CONFIG_BLK_DEV_MD
if (state->parts[p].flags & ADDPART_FLAG_RAID)
md_autodetect_dev(part_to_dev(part)->devt);
#endif
}
free_partitions(state);
return 0;
}
int invalidate_partitions(struct gendisk *disk, struct block_device *bdev)
{
int res;
if (!bdev->bd_invalidated)
return 0;
res = drop_partitions(disk, bdev);
if (res)
return res;
set_capacity(disk, 0);
check_disk_size_change(disk, bdev, false);
bdev->bd_invalidated = 0;
/* tell userspace that the media / partition table may have changed */
kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);
return 0;
}
unsigned char *read_dev_sector(struct block_device *bdev, sector_t n, Sector *p)
{
struct address_space *mapping = bdev->bd_inode->i_mapping;
struct page *page;
page = read_mapping_page(mapping, (pgoff_t)(n >> (PAGE_SHIFT-9)), NULL);
if (!IS_ERR(page)) {
if (PageError(page))
goto fail;
p->v = page;
return (unsigned char *)page_address(page) + ((n & ((1 << (PAGE_SHIFT - 9)) - 1)) << 9);
fail:
put_page(page);
}
p->v = NULL;
return NULL;
}
EXPORT_SYMBOL(read_dev_sector);