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block: Do not discard buffers under a mounted filesystem

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Discarding blocks and buffers under a mounted filesystem is hardly
anything admin wants to do. Usually it will confuse the filesystem and
sometimes the loss of buffer_head state (including b_private field) can
even cause crashes like:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
PGD 0 P4D 0
Oops: 0002 [#1] SMP PTI
CPU: 4 PID: 203778 Comm: jbd2/dm-3-8 Kdump: loaded Tainted: G O     --------- -  - 4.18.0-147.5.0.5.h126.eulerosv2r9.x86_64 #1
Hardware name: Huawei RH2288H V3/BC11HGSA0, BIOS 1.57 08/11/2015
RIP: 0010:jbd2_journal_grab_journal_head+0x1b/0x40 [jbd2]
...
Call Trace:
 __jbd2_journal_insert_checkpoint+0x23/0x70 [jbd2]
 jbd2_journal_commit_transaction+0x155f/0x1b60 [jbd2]
 kjournald2+0xbd/0x270 [jbd2]

So if we don't have block device open with O_EXCL already, claim the
block device while we truncate buffer cache. This makes sure any
exclusive block device user (such as filesystem) cannot operate on the
device while we are discarding buffer cache.

Reported-by: Ye Bin <yebin10@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
[axboe: fix !CONFIG_BLOCK error in truncate_bdev_range()]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jan Kara
2020-09-04 10:58:52 +02:00
committed by Jens Axboe
parent 6dbf7bb555
commit 384d87ef2c
3 changed files with 50 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/blkdev.h
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@@ -1987,11 +1987,18 @@ void bdput(struct block_device *);
#ifdef CONFIG_BLOCK
void invalidate_bdev(struct block_device *bdev);
int truncate_bdev_range(struct block_device *bdev, fmode_t mode, loff_t lstart,
loff_t lend);
int sync_blockdev(struct block_device *bdev);
#else
static inline void invalidate_bdev(struct block_device *bdev)
{
}
static inline int truncate_bdev_range(struct block_device *bdev, fmode_t mode,
loff_t lstart, loff_t lend)
{
return 0;
}
static inline int sync_blockdev(struct block_device *bdev)
{
return 0;