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SubjectRe: [PATCH v3 03/15] block, dax: fix lifetime of in-kernel dax mappings with dax_map_atomic()
On Sun, Nov 01, 2015 at 11:29:58PM -0500, Dan Williams wrote:
> 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: Jan Kara <jack@suse.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
<>
> @@ -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);

I think you can use dax_map_atomic() here instead, allowing you to avoid
having a local pfn variable that otherwise goes unused.

> @@ -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);

Same as above, you can use dax_map_atomic() here instead and nix the pfn variable.

> @@ -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);

Just a note that we lost the check for bdev_direct_access() returning less
than PAGE_SIZE. Are we sure this can't happen and that it's safe to remove
the check?

> @@ -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);

Let's use PMD_SIZE instead of HPAGE_SIZE to be consistent with the rest of the
DAX code.

> +
> + 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);

Ditto, let's use PMD_SIZE for consistency (I realize this was changed ealier
in the series).


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