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Subject[PATCH 3/5] block, dax: fix lifetime of in-kernel dax mappings with dax_map_atomic()
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The DAX implementation needs to protect new calls to ->direct_access()
and usage of its return value against unbind of the underlying block
device. Use blk_queue_enter()/blk_queue_exit() to either prevent
blk_cleanup_queue() from proceeding, or fail the dax_map_atomic() if the
request_queue is being torn down.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
block/blk.h | 2 -
fs/dax.c | 165 ++++++++++++++++++++++++++++++++----------------
include/linux/blkdev.h | 2 +
3 files changed, 112 insertions(+), 57 deletions(-)

diff --git a/block/blk.h b/block/blk.h
index 157c93d54dc9..dc7d9411fa45 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -72,8 +72,6 @@ void blk_dequeue_request(struct request *rq);
void __blk_queue_free_tags(struct request_queue *q);
bool __blk_end_bidi_request(struct request *rq, int error,
unsigned int nr_bytes, unsigned int bidi_bytes);
-int blk_queue_enter(struct request_queue *q, gfp_t gfp);
-void blk_queue_exit(struct request_queue *q);
void blk_freeze_queue(struct request_queue *q);

static inline void blk_queue_enter_live(struct request_queue *q)
diff --git a/fs/dax.c b/fs/dax.c
index f8e543839e5c..a480729c00ec 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -30,6 +30,40 @@
#include <linux/vmstat.h>
#include <linux/sizes.h>

+static void __pmem *__dax_map_atomic(struct block_device *bdev, sector_t sector,
+ long size, unsigned long *pfn, long *len)
+{
+ long rc;
+ void __pmem *addr;
+ struct request_queue *q = bdev->bd_queue;
+
+ if (blk_queue_enter(q, GFP_NOWAIT) != 0)
+ return (void __pmem *) ERR_PTR(-EIO);
+ rc = bdev_direct_access(bdev, sector, &addr, pfn, size);
+ if (len)
+ *len = rc;
+ if (rc < 0) {
+ blk_queue_exit(q);
+ return (void __pmem *) ERR_PTR(rc);
+ }
+ return addr;
+}
+
+static void __pmem *dax_map_atomic(struct block_device *bdev, sector_t sector,
+ long size)
+{
+ unsigned long pfn;
+
+ return __dax_map_atomic(bdev, sector, size, &pfn, NULL);
+}
+
+static void dax_unmap_atomic(struct block_device *bdev, void __pmem *addr)
+{
+ if (IS_ERR(addr))
+ return;
+ blk_queue_exit(bdev->bd_queue);
+}
+
int dax_clear_blocks(struct inode *inode, sector_t block, long size)
{
struct block_device *bdev = inode->i_sb->s_bdev;
@@ -42,9 +76,9 @@ int dax_clear_blocks(struct inode *inode, sector_t block, long size)
long count, sz;

sz = min_t(long, size, SZ_1M);
- count = bdev_direct_access(bdev, sector, &addr, &pfn, sz);
- if (count < 0)
- return count;
+ addr = __dax_map_atomic(bdev, sector, size, &pfn, &count);
+ if (IS_ERR(addr))
+ return PTR_ERR(addr);
if (count < sz)
sz = count;
clear_pmem(addr, sz);
@@ -52,6 +86,7 @@ int dax_clear_blocks(struct inode *inode, sector_t block, long size)
size -= sz;
BUG_ON(sz & 511);
sector += sz / 512;
+ dax_unmap_atomic(bdev, addr);
cond_resched();
} while (size);

@@ -60,14 +95,6 @@ int dax_clear_blocks(struct inode *inode, sector_t block, long size)
}
EXPORT_SYMBOL_GPL(dax_clear_blocks);

-static long dax_get_addr(struct buffer_head *bh, void __pmem **addr,
- unsigned blkbits)
-{
- unsigned long pfn;
- sector_t sector = bh->b_blocknr << (blkbits - 9);
- return bdev_direct_access(bh->b_bdev, sector, addr, &pfn, bh->b_size);
-}
-
/* the clear_pmem() calls are ordered by a wmb_pmem() in the caller */
static void dax_new_buf(void __pmem *addr, unsigned size, unsigned first,
loff_t pos, loff_t end)
@@ -97,19 +124,30 @@ static bool buffer_size_valid(struct buffer_head *bh)
return bh->b_state != 0;
}

+
+static sector_t to_sector(const struct buffer_head *bh,
+ const struct inode *inode)
+{
+ sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
+
+ return sector;
+}
+
static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
loff_t start, loff_t end, get_block_t get_block,
struct buffer_head *bh)
{
- ssize_t retval = 0;
- loff_t pos = start;
- loff_t max = start;
- loff_t bh_max = start;
- void __pmem *addr;
+ loff_t pos = start, max = start, bh_max = start;
+ struct block_device *bdev = NULL;
+ int rw = iov_iter_rw(iter), rc;
+ long map_len = 0;
+ unsigned long pfn;
+ void __pmem *addr = NULL;
+ void __pmem *kmap = (void __pmem *) ERR_PTR(-EIO);
bool hole = false;
bool need_wmb = false;

- if (iov_iter_rw(iter) != WRITE)
+ if (rw == READ)
end = min(end, i_size_read(inode));

while (pos < end) {
@@ -124,13 +162,13 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
if (pos == bh_max) {
bh->b_size = PAGE_ALIGN(end - pos);
bh->b_state = 0;
- retval = get_block(inode, block, bh,
- iov_iter_rw(iter) == WRITE);
- if (retval)
+ rc = get_block(inode, block, bh, rw == WRITE);
+ if (rc)
break;
if (!buffer_size_valid(bh))
bh->b_size = 1 << blkbits;
bh_max = pos - first + bh->b_size;
+ bdev = bh->b_bdev;
} else {
unsigned done = bh->b_size -
(bh_max - (pos - first));
@@ -138,21 +176,27 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
bh->b_size -= done;
}

- hole = iov_iter_rw(iter) != WRITE && !buffer_written(bh);
+ hole = rw == READ && !buffer_written(bh);
if (hole) {
addr = NULL;
size = bh->b_size - first;
} else {
- retval = dax_get_addr(bh, &addr, blkbits);
- if (retval < 0)
+ dax_unmap_atomic(bdev, kmap);
+ kmap = __dax_map_atomic(bdev,
+ to_sector(bh, inode),
+ bh->b_size, &pfn, &map_len);
+ if (IS_ERR(kmap)) {
+ rc = PTR_ERR(kmap);
break;
+ }
+ addr = kmap;
if (buffer_unwritten(bh) || buffer_new(bh)) {
- dax_new_buf(addr, retval, first, pos,
- end);
+ dax_new_buf(addr, map_len, first, pos,
+ end);
need_wmb = true;
}
addr += first;
- size = retval - first;
+ size = map_len - first;
}
max = min(pos + size, end);
}
@@ -175,8 +219,9 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,

if (need_wmb)
wmb_pmem();
+ dax_unmap_atomic(bdev, kmap);

- return (pos == start) ? retval : pos - start;
+ return (pos == start) ? rc : pos - start;
}

/**
@@ -265,28 +310,31 @@ static int dax_load_hole(struct address_space *mapping, struct page *page,
return VM_FAULT_LOCKED;
}

-static int copy_user_bh(struct page *to, struct buffer_head *bh,
- unsigned blkbits, unsigned long vaddr)
+static int copy_user_bh(struct page *to, struct inode *inode,
+ struct buffer_head *bh, unsigned long vaddr)
{
+ struct block_device *bdev = bh->b_bdev;
void __pmem *vfrom;
void *vto;

- if (dax_get_addr(bh, &vfrom, blkbits) < 0)
- return -EIO;
+ vfrom = dax_map_atomic(bdev, to_sector(bh, inode), bh->b_size);
+ if (IS_ERR(vfrom))
+ return PTR_ERR(vfrom);
vto = kmap_atomic(to);
copy_user_page(vto, (void __force *)vfrom, vaddr, to);
kunmap_atomic(vto);
+ dax_unmap_atomic(bdev, vfrom);
return 0;
}

static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
struct vm_area_struct *vma, struct vm_fault *vmf)
{
- struct address_space *mapping = inode->i_mapping;
- sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
unsigned long vaddr = (unsigned long)vmf->virtual_address;
- void __pmem *addr;
+ struct address_space *mapping = inode->i_mapping;
+ struct block_device *bdev = bh->b_bdev;
unsigned long pfn;
+ void __pmem *addr;
pgoff_t size;
int error;

@@ -305,11 +353,10 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
goto out;
}

- error = bdev_direct_access(bh->b_bdev, sector, &addr, &pfn, bh->b_size);
- if (error < 0)
- goto out;
- if (error < PAGE_SIZE) {
- error = -EIO;
+ addr = __dax_map_atomic(bdev, to_sector(bh, inode), bh->b_size,
+ &pfn, NULL);
+ if (IS_ERR(addr)) {
+ error = PTR_ERR(addr);
goto out;
}

@@ -317,6 +364,7 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
clear_pmem(addr, PAGE_SIZE);
wmb_pmem();
}
+ dax_unmap_atomic(bdev, addr);

error = vm_insert_mixed(vma, vaddr, pfn);

@@ -412,7 +460,7 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
if (vmf->cow_page) {
struct page *new_page = vmf->cow_page;
if (buffer_written(&bh))
- error = copy_user_bh(new_page, &bh, blkbits, vaddr);
+ error = copy_user_bh(new_page, inode, &bh, vaddr);
else
clear_user_highpage(new_page, vaddr);
if (error)
@@ -524,11 +572,9 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
unsigned blkbits = inode->i_blkbits;
unsigned long pmd_addr = address & PMD_MASK;
bool write = flags & FAULT_FLAG_WRITE;
- long length;
- void __pmem *kaddr;
+ struct block_device *bdev;
pgoff_t size, pgoff;
- sector_t block, sector;
- unsigned long pfn;
+ sector_t block;
int result = 0;

/* Fall back to PTEs if we're going to COW */
@@ -552,9 +598,9 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);

bh.b_size = PMD_SIZE;
- length = get_block(inode, block, &bh, write);
- if (length)
+ if (get_block(inode, block, &bh, write) != 0)
return VM_FAULT_SIGBUS;
+ bdev = bh.b_bdev;
i_mmap_lock_read(mapping);

/*
@@ -609,15 +655,20 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
result = VM_FAULT_NOPAGE;
spin_unlock(ptl);
} else {
- sector = bh.b_blocknr << (blkbits - 9);
- length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
- bh.b_size);
- if (length < 0) {
+ long length;
+ unsigned long pfn;
+ void __pmem *kaddr = __dax_map_atomic(bdev,
+ to_sector(&bh, inode), HPAGE_SIZE, &pfn,
+ &length);
+
+ if (IS_ERR(kaddr)) {
result = VM_FAULT_SIGBUS;
goto out;
}
- if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
+ if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR)) {
+ dax_unmap_atomic(bdev, kaddr);
goto fallback;
+ }

if (buffer_unwritten(&bh) || buffer_new(&bh)) {
clear_pmem(kaddr, HPAGE_SIZE);
@@ -626,6 +677,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
result |= VM_FAULT_MAJOR;
}
+ dax_unmap_atomic(bdev, kaddr);

result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write);
}
@@ -729,12 +781,15 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
if (err < 0)
return err;
if (buffer_written(&bh)) {
- void __pmem *addr;
- err = dax_get_addr(&bh, &addr, inode->i_blkbits);
- if (err < 0)
- return err;
+ struct block_device *bdev = bh.b_bdev;
+ void __pmem *addr = dax_map_atomic(bdev, to_sector(&bh, inode),
+ PAGE_CACHE_SIZE);
+
+ if (IS_ERR(addr))
+ return PTR_ERR(addr);
clear_pmem(addr + offset, length);
wmb_pmem();
+ dax_unmap_atomic(bdev, addr);
}

return 0;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index cf57884db4b7..59a770dad804 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -792,6 +792,8 @@ extern int scsi_cmd_ioctl(struct request_queue *, struct gendisk *, fmode_t,
extern int sg_scsi_ioctl(struct request_queue *, struct gendisk *, fmode_t,
struct scsi_ioctl_command __user *);

+extern int blk_queue_enter(struct request_queue *q, gfp_t gfp);
+extern void blk_queue_exit(struct request_queue *q);
extern void blk_start_queue(struct request_queue *q);
extern void blk_stop_queue(struct request_queue *q);
extern void blk_sync_queue(struct request_queue *q);


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