On Wed, May 02, 2018 at 11:14:45PM +0200, Christoph Hellwig wrote:
> If we release the lockdep write protection token before calling into
> ->write_iter and thus never access the file pointer after an -EIOCBQUEUED
> return from ->write_iter or ->read_iter we don't need this extra
> reference.
>
> Signed-off-by: Christoph Hellwig <h...@lst.de>
LGTM,
Reviewed-by: Darrick J. Wong <darrick.w...@oracle.com>
--D
> ---
> fs/aio.c | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 18507743757a..e5866e2fc331 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1515,16 +1515,19 @@ static ssize_t aio_write(struct kiocb *req, struct
> iocb *iocb, bool vectored,
> return ret;
> ret = rw_verify_area(WRITE, file, &req->ki_pos, iov_iter_count(&iter));
> if (!ret) {
> - req->ki_flags |= IOCB_WRITE;
> - file_start_write(file);
> - ret = aio_ret(req, call_write_iter(file, req, &iter));
> /*
> - * We release freeze protection in aio_complete(). Fool lockdep
> - * by telling it the lock got released so that it doesn't
> - * complain about held lock when we return to userspace.
> + * Open-code file_start_write here to grab freeze protection,
> + * which will be released by another thread in aio_complete().
> + * Fool lockdep by telling it the lock got released so that it
> + * doesn't complain about the held lock when we return to
> + * userspace.
> */
> - if (S_ISREG(file_inode(file)->i_mode))
> + if (S_ISREG(file_inode(file)->i_mode)) {
> + __sb_start_write(file_inode(file)->i_sb,
> SB_FREEZE_WRITE, true);
> __sb_writers_release(file_inode(file)->i_sb,
> SB_FREEZE_WRITE);
> + }
> + req->ki_flags |= IOCB_WRITE;
> + ret = aio_ret(req, call_write_iter(file, req, &iter));
> }
> kfree(iovec);
> return ret;
> @@ -1599,7 +1602,6 @@ static int io_submit_one(struct kioctx *ctx, struct
> iocb __user *user_iocb,
> req->ki_user_iocb = user_iocb;
> req->ki_user_data = iocb->aio_data;
>
> - get_file(file);
> switch (iocb->aio_lio_opcode) {
> case IOCB_CMD_PREAD:
> ret = aio_read(&req->common, iocb, false, compat);
> @@ -1618,8 +1620,13 @@ static int io_submit_one(struct kioctx *ctx, struct
> iocb __user *user_iocb,
> ret = -EINVAL;
> break;
> }
> - fput(file);
>
> + /*
> + * If ret is -EIOCBQUEUED, ownership of the file reference acquired
> + * above passed to the file system, which at this point might have
> + * dropped the reference, so we must be careful to not reference it
> + * once we have called into the file system.
> + */
> if (ret && ret != -EIOCBQUEUED)
> goto out_put_req;
> return 0;
> --
> 2.17.0
>
> --
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