From b87570f5d349661814b262dd5fc40787700f80d6 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Wed, 26 Sep 2012 07:46:40 +0200 Subject: Fix a crash when block device is read and block size is changed at the same time The kernel may crash when block size is changed and I/O is issued simultaneously. Because some subsystems (udev or lvm) may read any block device anytime, the bug actually puts any code that changes a block device size in jeopardy. The crash can be reproduced if you place "msleep(1000)" to blkdev_get_blocks just before "bh->b_size = max_blocks << inode->i_blkbits;". Then, run "dd if=/dev/ram0 of=/dev/null bs=4k count=1 iflag=direct" While it is waiting in msleep, run "blockdev --setbsz 2048 /dev/ram0" You get a BUG. The direct and non-direct I/O is written with the assumption that block size does not change. It doesn't seem practical to fix these crashes one-by-one there may be many crash possibilities when block size changes at a certain place and it is impossible to find them all and verify the code. This patch introduces a new rw-lock bd_block_size_semaphore. The lock is taken for read during I/O. It is taken for write when changing block size. Consequently, block size can't be changed while I/O is being submitted. For asynchronous I/O, the patch only prevents block size change while the I/O is being submitted. The block size can change when the I/O is in progress or when the I/O is being finished. This is acceptable because there are no accesses to block size when asynchronous I/O is being finished. The patch prevents block size changing while the device is mapped with mmap. Signed-off-by: Mikulas Patocka Signed-off-by: Jens Axboe --- drivers/char/raw.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/char/raw.c') diff --git a/drivers/char/raw.c b/drivers/char/raw.c index 54a3a6d..0bb207e 100644 --- a/drivers/char/raw.c +++ b/drivers/char/raw.c @@ -285,7 +285,7 @@ static long raw_ctl_compat_ioctl(struct file *file, unsigned int cmd, static const struct file_operations raw_fops = { .read = do_sync_read, - .aio_read = generic_file_aio_read, + .aio_read = blkdev_aio_read, .write = do_sync_write, .aio_write = blkdev_aio_write, .fsync = blkdev_fsync, -- cgit v1.1