diff options
| author | Mikulas Patocka <mpatocka@redhat.com> | 2012-09-26 07:46:40 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2012-09-26 07:46:40 +0200 |
| commit | b87570f5d349661814b262dd5fc40787700f80d6 (patch) | |
| tree | d06ef6c95ed114e19c864ebe0240c788dd75e85c /drivers/char | |
| parent | 60ea8226cbd5c8301f9a39edc574ddabcb8150e0 (diff) | |
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 <mpatocka@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/char')
| -rw-r--r-- | drivers/char/raw.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/char/raw.c b/drivers/char/raw.c index 54a3a6d09819..0bb207eaef2f 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, |