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Subject: Re: [PATCH v5 08/12] ext4: update direct I/O read to do trylock in
 IOCB_NOWAIT cases
To:     Matthew Bobrowski <mbobrowski@mbobrowski.org>, tytso@mit.edu,
        jack@suse.cz, adilger.kernel@dilger.ca
Cc:     linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        hch@infradead.org, david@fromorbit.com, darrick.wong@oracle.com
References: <cover.1571647178.git.mbobrowski@mbobrowski.org>
 <5ee370a435eb08fb14579c7c197b16e9fa0886f0.1571647179.git.mbobrowski@mbobrowski.org>
From:   Ritesh Harjani <riteshh@linux.ibm.com>
Date:   Wed, 23 Oct 2019 12:21:10 +0530
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On 10/21/19 2:48 PM, Matthew Bobrowski wrote:
> This patch updates the lock pattern in ext4_dio_read_iter() to only
> perform the trylock in IOCB_NOWAIT cases.
> 
> Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>

This shall need a rebase (as mentioned in patch-1 discussion).
It will be good to mention that the locking condition
is kept similar to 942491c9e6d6 ("xfs: fix AIM7 regression").

Also, I think it may also need a fixes tag.
It seems unconditional inode_lock_shared was added by below commit.

Fixes: 16c54688592c ("ext4: Allow parallel DIO reads")


Otherwise, this patch looks good to me. You may add:

Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>


> ---
>   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);
>   		/*
>