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block: fix race between set_blocksize and read paths

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With the new large sector size support, it's now the case that
set_blocksize can change i_blksize and the folio order in a manner that
conflicts with a concurrent reader and causes a kernel crash.

Specifically, let's say that udev-worker calls libblkid to detect the
labels on a block device.  The read call can create an order-0 folio to
read the first 4096 bytes from the disk.  But then udev is preempted.

Next, someone tries to mount an 8k-sectorsize filesystem from the same
block device.  The filesystem calls set_blksize, which sets i_blksize to
8192 and the minimum folio order to 1.

Now udev resumes, still holding the order-0 folio it allocated.  It then
tries to schedule a read bio and do_mpage_readahead tries to create
bufferheads for the folio.  Unfortunately, blocks_per_folio == 0 because
the page size is 4096 but the blocksize is 8192 so no bufferheads are
attached and the bh walk never sets bdev.  We then submit the bio with a
NULL block device and crash.

Therefore, truncate the page cache after flushing but before updating
i_blksize.  However, that's not enough -- we also need to lock out file
IO and page faults during the update.  Take both the i_rwsem and the
invalidate_lock in exclusive mode for invalidations, and in shared mode
for read/write operations.

I don't know if this is the correct fix, but xfs/259 found it.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/174543795699.4139148.2086129139322431423.stgit@frogsfrogsfrogs
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Darrick J. Wong 2025-04-23 12:53:42 -07:00 • committed by Jens Axboe
parent 81dd1feb19
commit c0e473a0d2
4 changed files with 43 additions and 1 deletions
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17
block/bdev.c
View file

@ -169,10 +169,27 @@ int set_blocksize(struct file *file, int size)
/* Don't change the size if it is same as current */
if (inode->i_blkbits != blksize_bits(size)) {
/*
* Flush and truncate the pagecache before we reconfigure the
* mapping geometry because folio sizes are variable now. If a
* reader has already allocated a folio whose size is smaller
* than the new min_order but invokes readahead after the new
* min_order becomes visible, readahead will think there are
* "zero" blocks per folio and crash. Take the inode and
* invalidation locks to avoid racing with
* read/write/fallocate.
*/
inode_lock(inode);
filemap_invalidate_lock(inode->i_mapping);
sync_blockdev(bdev);
kill_bdev(bdev);
inode->i_blkbits = blksize_bits(size);
mapping_set_folio_min_order(inode->i_mapping, get_order(size));
kill_bdev(bdev);
filemap_invalidate_unlock(inode->i_mapping);
inode_unlock(inode);
}
return 0;
}

5
block/blk-zoned.c
View file

@ -343,6 +343,7 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, blk_mode_t mode,
op = REQ_OP_ZONE_RESET;
/* Invalidate the page cache, including dirty pages. */
inode_lock(bdev->bd_mapping->host);
filemap_invalidate_lock(bdev->bd_mapping);
ret = blkdev_truncate_zone_range(bdev, mode, &zrange);
if (ret)
@ -364,8 +365,10 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, blk_mode_t mode,
ret = blkdev_zone_mgmt(bdev, op, zrange.sector, zrange.nr_sectors);
fail:
if (cmd == BLKRESETZONE)
if (cmd == BLKRESETZONE) {
filemap_invalidate_unlock(bdev->bd_mapping);
inode_unlock(bdev->bd_mapping->host);
}
return ret;
}

16
block/fops.c
View file

@ -746,7 +746,14 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
ret = direct_write_fallback(iocb, from, ret,
blkdev_buffered_write(iocb, from));
} else {
/*
* Take i_rwsem and invalidate_lock to avoid racing with
* set_blocksize changing i_blkbits/folio order and punching
* out the pagecache.
*/
inode_lock_shared(bd_inode);
ret = blkdev_buffered_write(iocb, from);
inode_unlock_shared(bd_inode);
}
if (ret > 0)
@ -757,6 +764,7 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
struct inode *bd_inode = bdev_file_inode(iocb->ki_filp);
struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host);
loff_t size = bdev_nr_bytes(bdev);
loff_t pos = iocb->ki_pos;
@ -793,7 +801,13 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
goto reexpand;
}
/*
* Take i_rwsem and invalidate_lock to avoid racing with set_blocksize
* changing i_blkbits/folio order and punching out the pagecache.
*/
inode_lock_shared(bd_inode);
ret = filemap_read(iocb, to, ret);
inode_unlock_shared(bd_inode);
reexpand:
if (unlikely(shorted))
@ -836,6 +850,7 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
if ((start | len) & (bdev_logical_block_size(bdev) - 1))
return -EINVAL;
inode_lock(inode);
filemap_invalidate_lock(inode->i_mapping);
/*
@ -868,6 +883,7 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
fail:
filemap_invalidate_unlock(inode->i_mapping);
inode_unlock(inode);
return error;
}

6
block/ioctl.c
View file

@ -142,6 +142,7 @@ static int blk_ioctl_discard(struct block_device *bdev, blk_mode_t mode,
if (err)
return err;
inode_lock(bdev->bd_mapping->host);
filemap_invalidate_lock(bdev->bd_mapping);
err = truncate_bdev_range(bdev, mode, start, start + len - 1);
if (err)
@ -174,6 +175,7 @@ out_unplug:
blk_finish_plug(&plug);
fail:
filemap_invalidate_unlock(bdev->bd_mapping);
inode_unlock(bdev->bd_mapping->host);
return err;
}
@ -199,12 +201,14 @@ static int blk_ioctl_secure_erase(struct block_device *bdev, blk_mode_t mode,
end > bdev_nr_bytes(bdev))
return -EINVAL;
inode_lock(bdev->bd_mapping->host);
filemap_invalidate_lock(bdev->bd_mapping);
err = truncate_bdev_range(bdev, mode, start, end - 1);
if (!err)
err = blkdev_issue_secure_erase(bdev, start >> 9, len >> 9,
GFP_KERNEL);
filemap_invalidate_unlock(bdev->bd_mapping);
inode_unlock(bdev->bd_mapping->host);
return err;
}
@ -236,6 +240,7 @@ static int blk_ioctl_zeroout(struct block_device *bdev, blk_mode_t mode,
return -EINVAL;
/* Invalidate the page cache, including dirty pages */
inode_lock(bdev->bd_mapping->host);
filemap_invalidate_lock(bdev->bd_mapping);
err = truncate_bdev_range(bdev, mode, start, end);
if (err)
@ -246,6 +251,7 @@ static int blk_ioctl_zeroout(struct block_device *bdev, blk_mode_t mode,
fail:
filemap_invalidate_unlock(bdev->bd_mapping);
inode_unlock(bdev->bd_mapping->host);
return err;
}