From: Jan Kara jack@suse.cz
mainline inclusion from mainline-5.12-rc1 commit 767630c63bb23acf022adb265574996ca39a4645 category: bugfix bugzilla: 107770 CVE: NA
-------------------------------------------------
blkdev_fallocate() tries to detect whether a discard raced with an overlapping write by calling invalidate_inode_pages2_range(). However this check can give both false negatives (when writing using direct IO or when writeback already writes out the written pagecache range) and false positives (when write is not actually overlapping but ends in the same page when blocksize < pagesize). This actually causes issues for qemu which is getting confused by EBUSY errors.
Fix the problem by removing this conflicting write detection since it is inherently racy and thus of little use anyway.
Reported-by: Maxim Levitsky mlevitsk@redhat.com CC: "Darrick J. Wong" darrick.wong@oracle.com Link: https://lore.kernel.org/qemu-devel/20201111153913.41840-1-mlevitsk@redhat.co... Signed-off-by: Jan Kara jack@suse.cz Reviewed-by: Maxim Levitsky mlevitsk@redhat.com Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Baokun Li libaokun1@huawei.com Reviewed-by: Zhang Yi yi.zhang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- fs/block_dev.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/fs/block_dev.c b/fs/block_dev.c index 30dd7b19bd2e3..06f73a1a1f66b 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -2174,13 +2174,11 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start, return error;
/* - * Invalidate again; if someone wandered in and dirtied a page, - * the caller will be given -EBUSY. The third argument is - * inclusive, so the rounding here is safe. + * Invalidate the page cache again; if someone wandered in and dirtied + * a page, we just discard it - userspace has no way of knowing whether + * the write happened before or after discard completing... */ - return invalidate_inode_pages2_range(bdev->bd_inode->i_mapping, - start >> PAGE_SHIFT, - end >> PAGE_SHIFT); + return truncate_bdev_range(bdev, file->f_mode, start, end); }
const struct file_operations def_blk_fops = {