On Thu, Mar 19, 2020 at 10:53:22AM +0200, Nikolay Borisov wrote:
>
>
> On 9.03.20 г. 23:32 ч., Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@xxxxxx>
> >
> > Currently, direct I/O has its own versions of bio_readpage_error() and
> > btrfs_check_repairable() (dio_read_error() and
> > btrfs_check_dio_repairable(), respectively). The main difference is that
> > the direct I/O version doesn't do read validation. The rework of direct
> > I/O repair makes it possible to do validation, so we can get rid of
> > btrfs_check_dio_repairable() and combine bio_readpage_error() and
> > dio_read_error() into a new helper, btrfs_submit_read_repair().
> >
> > Signed-off-by: Omar Sandoval <osandov@xxxxxx>
> > ---
> > fs/btrfs/extent_io.c | 126 +++++++++++++++++++------------------------
> > fs/btrfs/extent_io.h | 17 +++---
> > fs/btrfs/inode.c | 103 ++++-------------------------------
> > 3 files changed, 76 insertions(+), 170 deletions(-)
> >
> > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> > index fad86ef4d09d..a5cbe04da803 100644
> > --- a/fs/btrfs/extent_io.c
> > +++ b/fs/btrfs/extent_io.c
>
> <snip>
>
> > -/*
> > - * This is a generic handler for readpage errors. If other copies exist, read
> > - * those and write back good data to the failed position. Does not investigate
> > - * in remapping the failed extent elsewhere, hoping the device will be smart
> > - * enough to do this as needed
> > - */
> > -static int bio_readpage_error(struct bio *failed_bio, u64 phy_offset,
> > - struct page *page, u64 start, u64 end,
> > - int failed_mirror)
> > +blk_status_t btrfs_submit_read_repair(struct inode *inode,
> > + struct bio *failed_bio, u64 phy_offset,
> > + struct page *page, unsigned int pgoff,
> > + u64 start, u64 end, int failed_mirror,
> > + submit_bio_hook_t *submit_bio_hook)
> > {
> > struct io_failure_record *failrec;
> > - struct inode *inode = page->mapping->host;
> > + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > struct extent_io_tree *tree = &BTRFS_I(inode)->io_tree;
> > struct extent_io_tree *failure_tree = &BTRFS_I(inode)->io_failure_tree;
> > + struct btrfs_io_bio *failed_io_bio = btrfs_io_bio(failed_bio);
> > + struct btrfs_io_bio *io_bio;
> > + int icsum = phy_offset >> inode->i_sb->s_blocksize_bits;
> > bool need_validation = false;
> > struct bio *bio;
> > - int read_mode = 0;
> > blk_status_t status;
> > int ret;
> >
> > + btrfs_info(btrfs_sb(inode->i_sb),
> > + "Repair Read Error: read error at %llu", start);
> > +
> > BUG_ON(bio_op(failed_bio) == REQ_OP_WRITE);
> >
> > ret = btrfs_get_io_failure_record(inode, start, end, &failrec);
> > if (ret)
> > - return ret;
> > + return errno_to_blk_status(ret);
> >
> > /*
> > * If there was an I/O error and the I/O was for multiple sectors, we
> > * need to validate each sector individually.
> > */
> > if (failed_bio->bi_status != BLK_STS_OK) {
>
> Is this correct though, in case of buffered reads we are always called
> with bi_status != BLK_STS_OK (we are called from end_bio_extent_readpage
> in case uptodate is false, which happens if failed_bio->bi_status is
> non-zero. Additionally the bio is guaranteed to not be cloned because
> there is : ASSERT(!bio_flagged(bio, BIO_CLONED));
>
> The end effect of all of this is in case of buffered bios we never set
> need_revalidate, is this intentional?
For buffered I/O, this is called when bi_status != BLK_STS_OK OR
readpage_end_io_hook (i.e., check_data_csum()) failed. This check
distinguishes between those two cases: if we didn't hit an I/O error
(bi_status == BLK_STS_OK), then we don't need validation, otherwise, we
need validation if the bio is more than one sector.
> > - u64 len = 0;
> > - int i;
> > -
> > - for (i = 0; i < failed_bio->bi_vcnt; i++) {
> > - len += failed_bio->bi_io_vec[i].bv_len;
> > - if (len > inode->i_sb->s_blocksize) {
> > + if (bio_flagged(failed_bio, BIO_CLONED)) {
>
> If I understand this correctly this is the "this is a DIO " branch. IMO
> it'd be clearer if you had bool is_dio = bio_flagged(failed_bio,
> BIO_CLONED) at the top of the function and you used that.
Repair bios for direct I/O aren't cloned, so is_dio isn't accurate. IMO
it shouldn't matter whether it came from direct I/O or not. If it's a
cloned bio, you get the size out of io_bio->iter, and if it's not, you
get it out of bi_io_vec.
> > + if (failed_io_bio->iter.bi_size >
> > + inode->i_sb->s_blocksize)
> > need_validation = true;
> > - break;
> > + } else {
>
> This branch will only ever be executed in case of DIO with csum failure.
> So either add a comment to demarcate when various leaves of the 2 'if'
> should be called or, and I think this would be the better solution,
> rewrite it.
As commented above, this outer branch is for I/O errors (not checksum
errors), and this specific branch is for non-cloned bios, which happens
to be buffered read bios and buffered or direct I/O repair bios. Would
it be clearer as:
static u64 btrfs_bio_size(struct bio *bio)
{
if (bio_flagged(bio, BIO_CLONED))
return bio->iter.bi_size;
else
return bio_size_all(bio);
}
blk_status_t btrfs_submit_read_repair(...)
{
...
/*
* If there was an I/O error and the I/O was for multiple sectors, we
* need to validate each sector individually.
*/
need_validation = (failed_bio->bi_status != BLK_STS_OK &&
btrfs_bio_size() > inode->i_sb->s_blocksize);
...
}
