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 /include | |
| 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 'include')
| -rw-r--r-- | include/linux/fs.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h index bd6f6e7ca48..e60bbd0225d 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -725,6 +725,8 @@ struct block_device { int bd_fsfreeze_count; /* Mutex for freeze */ struct mutex bd_fsfreeze_mutex; + /* A semaphore that prevents I/O while block size is being changed */ + struct rw_semaphore bd_block_size_semaphore; }; /* @@ -2565,6 +2567,8 @@ extern int generic_segment_checks(const struct iovec *iov, unsigned long *nr_segs, size_t *count, int access_flags); /* fs/block_dev.c */ +extern ssize_t blkdev_aio_read(struct kiocb *iocb, const struct iovec *iov, + unsigned long nr_segs, loff_t pos); extern ssize_t blkdev_aio_write(struct kiocb *iocb, const struct iovec *iov, unsigned long nr_segs, loff_t pos); extern int blkdev_fsync(struct file *filp, loff_t start, loff_t end, |