On Thu 07-01-21 16:40:34, Jan Kara wrote: > 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@xxxxxxxxxx> > CC: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx> > Link: https://lore.kernel.org/qemu-devel/20201111153913.41840-1-mlevitsk@xxxxxxxxxx > Signed-off-by: Jan Kara <jack@xxxxxxx> Jens, can you please pick up this patch? Thanks! Honza > --- > 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 3e5b02f6606c..a97f43b49839 100644 > --- a/fs/block_dev.c > +++ b/fs/block_dev.c > @@ -1797,13 +1797,11 @@ 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 = { > -- > 2.26.2 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
