linux-ext4 - Re: [PATCH v5 08/12] ext4: update direct I/O read to do trylock in IOCB

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Date:   Mon, 21 Oct 2019 15:48:17 +0200
From:   Jan Kara <jack@...e.cz>
To:     Matthew Bobrowski <mbobrowski@...browski.org>
Cc:     tytso@....edu, jack@...e.cz, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: Re: [PATCH v5 08/12] ext4: update direct I/O read to do trylock in
 IOCB_NOWAIT cases

On Mon 21-10-19 20:18:46, Matthew Bobrowski wrote:
> This patch updates the lock pattern in ext4_dio_read_iter() to only
> perform the trylock in IOCB_NOWAIT cases.

The changelog is actually misleading. It should say something like "This
patch updates the lock pattern in ext4_dio_read_iter() to not block on
inode lock in case of IOCB_NOWAIT direct IO reads."

Also to ease backporting of easy fixes, we try to put patches like this
early in the series (fixing code in ext4_direct_IO_read(), and then the
fixed code would just carry over to ext4_dio_read_iter()).

The change itself looks good to me.

								Honza

> 
> Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
> ---
>  fs/ext4/file.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 6ea7e00e0204..8420686b90f5 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -52,7 +52,13 @@ static int ext4_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
>  	ssize_t ret;
>  	struct inode *inode = file_inode(iocb->ki_filp);
>  
> -	inode_lock_shared(inode);
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock_shared(inode))
> +			return -EAGAIN;
> +	} else {
> +		inode_lock_shared(inode);
> +	}
> +
>  	if (!ext4_dio_supported(inode)) {
>  		inode_unlock_shared(inode);
>  		/*
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR