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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Christoph Hellwig <hch@lst.de>
Cc: viro@zeniv.linux.org.uk, Avi Kivity <avi@scylladb.com>,
	linux-aio@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/7] aio: remove the extra get_file/fput pair in io_submit_one
Date: Wed, 2 May 2018 15:04:57 -0700	[thread overview]
Message-ID: <20180502220457.GB4116@magnolia> (raw)
In-Reply-To: <20180502211448.18276-5-hch@lst.de>

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 <hch@lst.de>

LGTM,
Reviewed-by: Darrick J. Wong <darrick.wong@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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  reply	other threads:[~2018-05-02 22:05 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-02 21:14 io_pgetevents & aio fsync V4 Christoph Hellwig
2018-05-02 21:14 ` [PATCH 1/7] aio: don't print the page size at boot time Christoph Hellwig
2018-05-02 21:14 ` [PATCH 2/7] aio: remove an outdated BUG_ON and comment in aio_complete Christoph Hellwig
2018-05-02 21:14 ` [PATCH 3/7] aio: sanitize ki_list handling Christoph Hellwig
2018-05-02 21:14 ` [PATCH 4/7] aio: remove the extra get_file/fput pair in io_submit_one Christoph Hellwig
2018-05-02 22:04   ` Darrick J. Wong [this message]
2018-05-02 21:14 ` [PATCH 5/7] aio: refactor read/write iocb setup Christoph Hellwig
2018-05-02 21:14 ` [PATCH 6/7] aio: implement IOCB_CMD_FSYNC and IOCB_CMD_FDSYNC Christoph Hellwig
2018-05-02 21:14 ` [PATCH 7/7] aio: implement io_pgetevents Christoph Hellwig
2018-05-18  8:28   ` James Hogan
2018-05-18  8:57     ` Christoph Hellwig
2018-07-04 14:21   ` Adrian Reber
2018-07-08 20:44     ` Christoph Hellwig
2018-07-09 17:20       ` Stephan Müller
2018-07-09 19:21       ` Stephan Müller
2018-07-10 12:51         ` Christoph Hellwig
2018-07-10  5:11       ` Andrei Vagin
2018-05-10 18:05 ` io_pgetevents & aio fsync V4 Al Viro
  -- strict thread matches above, loose matches on Subject: below --
2018-04-15 15:01 io_pgetevents & aio fsync V3 Christoph Hellwig
2018-04-15 15:01 ` [PATCH 4/7] aio: remove the extra get_file/fput pair in io_submit_one Christoph Hellwig
2018-04-26 15:41   ` Darrick J. Wong

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