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Subject: Re: [PATCH 2/3] ext4: fix inode rwsem regression
To:     Goldwyn Rodrigues <rgoldwyn@suse.de>, linux-fsdevel@vger.kernel.org
Cc:     linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org,
        hch@infradead.org, andres@anarazel.de, david@fromorbit.com,
        linux-f2fs-devel@lists.sourceforge.net,
        Goldwyn Rodrigues <rgoldwyn@suse.com>,
        Matthew Bobrowski <mbobrowski@mbobrowski.org>,
        aneesh.kumar@linux.ibm.com
References: <20190911093926.pfkkx25mffzeuo32@alap3.anarazel.de>
 <20190911164517.16130-1-rgoldwyn@suse.de>
 <20190911164517.16130-3-rgoldwyn@suse.de>
From:   Ritesh Harjani <riteshh@linux.ibm.com>
Date:   Thu, 12 Sep 2019 14:22:35 +0530
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cc'd Matthew as well.

On 9/11/19 10:15 PM, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> This is similar to 942491c9e6d6 ("xfs: fix AIM7 regression")
> Apparently our current rwsem code doesn't like doing the trylock, then
> lock for real scheme.  So change our read/write methods to just do the
> trylock for the RWF_NOWAIT case.
> 
> Fixes: 728fbc0e10b7 ("ext4: nowait aio support")
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>

This patch will conflict with recent iomap patch series.
So if this is getting queued up before, so iomap patch series will
need to rebase and factor these changes in the new APIs.

Otherwise looks good to me!

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


> ---
>   fs/ext4/file.c | 17 +++++++++++------
>   1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 70b0438dbc94..d5b2d0cc325d 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -40,11 +40,13 @@ static ssize_t ext4_dax_read_iter(struct kiocb *iocb, struct iov_iter *to)
>   	struct inode *inode = file_inode(iocb->ki_filp);
>   	ssize_t ret;
>   
> -	if (!inode_trylock_shared(inode)) {
> -		if (iocb->ki_flags & IOCB_NOWAIT)
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock_shared(inode))
>   			return -EAGAIN;
> +	} else {
>   		inode_lock_shared(inode);
>   	}
> +
>   	/*
>   	 * Recheck under inode lock - at this point we are sure it cannot
>   	 * change anymore
> @@ -190,11 +192,13 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   	struct inode *inode = file_inode(iocb->ki_filp);
>   	ssize_t ret;
>   
> -	if (!inode_trylock(inode)) {
> -		if (iocb->ki_flags & IOCB_NOWAIT)
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock(inode))
>   			return -EAGAIN;
> +	} else {
>   		inode_lock(inode);
>   	}
> +
>   	ret = ext4_write_checks(iocb, from);
>   	if (ret <= 0)
>   		goto out;
> @@ -233,9 +237,10 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   	if (!o_direct && (iocb->ki_flags & IOCB_NOWAIT))
>   		return -EOPNOTSUPP;
>   
> -	if (!inode_trylock(inode)) {
> -		if (iocb->ki_flags & IOCB_NOWAIT)
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock(inode))
>   			return -EAGAIN;
> +	} else {
>   		inode_lock(inode);
>   	}
>   
>