| Message ID | 20200921144353.31319-12-rgoldwyn@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | BTRFS DIO inode locking/D_SYNC fix | expand |
On 9/21/20 10:43 AM, Goldwyn Rodrigues wrote: > From: Goldwyn Rodrigues <rgoldwyn@suse.com> > > Direct writes within EOF are safe to be performed with inode shared lock > to improve parallelization with other direct writes or reads because EOF > is not changed and there is no race with truncate(). > > Direct reads are already performed under shared inode lock. > > This patch is precursor to removing btrfs_inode->dio_sem. > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> > --- > fs/btrfs/file.c | 33 +++++++++++++++++++++------------ > 1 file changed, 21 insertions(+), 12 deletions(-) > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > index d9c3be19d7b3..50092d24eee2 100644 > --- a/fs/btrfs/file.c > +++ b/fs/btrfs/file.c > @@ -1977,7 +1977,6 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); > loff_t pos; > ssize_t written = 0; > - bool relock = false; > ssize_t written_buffered; > loff_t endbyte; > int err; > @@ -1986,6 +1985,15 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) > if (iocb->ki_flags & IOCB_NOWAIT) > ilock_flags |= BTRFS_ILOCK_TRY; > > + /* > + * If the write DIO within EOF, use a shared lock > + */ > + if (iocb->ki_pos + iov_iter_count(from) <= i_size_read(inode)) > + ilock_flags |= BTRFS_ILOCK_SHARED; > + else if (iocb->ki_flags & IOCB_NOWAIT) > + return -EAGAIN; > + > +relock: Huh? Why are you making it so EOF extending NOWAIT writes now fail? We are still using ILOCK_TRY here, so we may still not block, am I missing something? Thanks, Josef
On 10:52 22/09, Josef Bacik wrote: > On 9/21/20 10:43 AM, Goldwyn Rodrigues wrote: > > From: Goldwyn Rodrigues <rgoldwyn@suse.com> > > > > Direct writes within EOF are safe to be performed with inode shared lock > > to improve parallelization with other direct writes or reads because EOF > > is not changed and there is no race with truncate(). > > > > Direct reads are already performed under shared inode lock. > > > > This patch is precursor to removing btrfs_inode->dio_sem. > > > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> > > --- > > fs/btrfs/file.c | 33 +++++++++++++++++++++------------ > > 1 file changed, 21 insertions(+), 12 deletions(-) > > > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > > index d9c3be19d7b3..50092d24eee2 100644 > > --- a/fs/btrfs/file.c > > +++ b/fs/btrfs/file.c > > @@ -1977,7 +1977,6 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) > > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); > > loff_t pos; > > ssize_t written = 0; > > - bool relock = false; > > ssize_t written_buffered; > > loff_t endbyte; > > int err; > > @@ -1986,6 +1985,15 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) > > if (iocb->ki_flags & IOCB_NOWAIT) > > ilock_flags |= BTRFS_ILOCK_TRY; > > + /* > > + * If the write DIO within EOF, use a shared lock > > + */ > > + if (iocb->ki_pos + iov_iter_count(from) <= i_size_read(inode)) > > + ilock_flags |= BTRFS_ILOCK_SHARED; > > + else if (iocb->ki_flags & IOCB_NOWAIT) > > + return -EAGAIN; > > + > > +relock: > > Huh? Why are you making it so EOF extending NOWAIT writes now fail? We are > still using ILOCK_TRY here, so we may still not block, am I missing > something? Thanks, > Yes, this is incorrect. I had thought of this would block on disk space allocations. But did not consider the prealloc case. I am removing this check to match the previous behavior.
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index d9c3be19d7b3..50092d24eee2 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1977,7 +1977,6 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); loff_t pos; ssize_t written = 0; - bool relock = false; ssize_t written_buffered; loff_t endbyte; int err; @@ -1986,6 +1985,15 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) if (iocb->ki_flags & IOCB_NOWAIT) ilock_flags |= BTRFS_ILOCK_TRY; + /* + * If the write DIO within EOF, use a shared lock + */ + if (iocb->ki_pos + iov_iter_count(from) <= i_size_read(inode)) + ilock_flags |= BTRFS_ILOCK_SHARED; + else if (iocb->ki_flags & IOCB_NOWAIT) + return -EAGAIN; + +relock: err = btrfs_inode_lock(inode, ilock_flags); if (err < 0) return err; @@ -1997,21 +2005,23 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) } pos = iocb->ki_pos; + /* + * Re-check since file size may have changed + * just before taking the lock or pos may have changed + * because of O_APPEND in generic_write_check() + */ + if ((ilock_flags & BTRFS_ILOCK_SHARED) && + pos + iov_iter_count(from) > i_size_read(inode)) { + btrfs_inode_unlock(inode, ilock_flags); + ilock_flags &= ~BTRFS_ILOCK_SHARED; + goto relock; + } if (check_direct_IO(fs_info, from, pos)) { btrfs_inode_unlock(inode, ilock_flags); goto buffered; } - /* - * If the write DIO is beyond the EOF, we need update - * the isize, but it is protected by i_mutex. So we can - * not unlock the i_mutex at this case. - */ - if (pos + iov_iter_count(from) <= inode->i_size) { - btrfs_inode_unlock(inode, 0); - relock = true; - } down_read(&BTRFS_I(inode)->dio_sem); /* @@ -2029,8 +2039,7 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) written = 0; up_read(&BTRFS_I(inode)->dio_sem); - if (relock) - btrfs_inode_lock(inode, 0); + btrfs_inode_unlock(inode, ilock_flags); if (written < 0 || !iov_iter_count(from)) { err = written;