Re: [PATCH 03/15] iomap: Allow filesystem to call iomap_dio_complete without i_rwsem

[Josef Bacik <josef@toxicpanda.com>]

On 9/21/20 10:43 AM, Goldwyn Rodrigues wrote:
> From: Christoph Hellwig <hch@lst.de>
> 
> This is to avoid the deadlock caused in btrfs because of O_DIRECT |
> O_DSYNC.
> 
> Filesystems such as btrfs require i_rwsem while performing sync on a
> file. iomap_dio_rw() is called under i_rw_sem. This leads to a
> deadlock because of:
> 
> iomap_dio_complete()
>    generic_write_sync()
>      btrfs_sync_file()
> 
> Separate out iomap_dio_complete() from iomap_dio_rw(), so filesystems
> can call iomap_dio_complete() after unlocking i_rwsem.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> ---
>   fs/iomap/direct-io.c  | 34 +++++++++++++++++++++++++---------
>   include/linux/iomap.h |  5 +++++
>   2 files changed, 30 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index c1aafb2ab990..d970c6bbbe11 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -76,7 +76,7 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
>   		dio->submit.cookie = submit_bio(bio);
>   }
>   
> -static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> +ssize_t iomap_dio_complete(struct iomap_dio *dio)
>   {
>   	const struct iomap_dio_ops *dops = dio->dops;
>   	struct kiocb *iocb = dio->iocb;
> @@ -130,6 +130,7 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
>   
>   	return ret;
>   }
> +EXPORT_SYMBOL_GPL(iomap_dio_complete);
>   
>   static void iomap_dio_complete_work(struct work_struct *work)
>   {
> @@ -406,8 +407,8 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
>    * Returns -ENOTBLK In case of a page invalidation invalidation failure for
>    * writes.  The callers needs to fall back to buffered I/O in this case.
>    */
> -ssize_t
> -iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> +struct iomap_dio *
> +__iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>   		const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
>   		bool wait_for_completion)
>   {
> @@ -421,14 +422,14 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>   	struct iomap_dio *dio;
>   
>   	if (!count)
> -		return 0;
> +		return NULL;
>   
>   	if (WARN_ON(is_sync_kiocb(iocb) && !wait_for_completion))
> -		return -EIO;
> +		return ERR_PTR(-EIO);
>   
>   	dio = kmalloc(sizeof(*dio), GFP_KERNEL);
>   	if (!dio)
> -		return -ENOMEM;
> +		return ERR_PTR(-ENOMEM);
>   
>   	dio->iocb = iocb;
>   	atomic_set(&dio->ref, 1);
> @@ -558,7 +559,7 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>   	dio->wait_for_completion = wait_for_completion;
>   	if (!atomic_dec_and_test(&dio->ref)) {
>   		if (!wait_for_completion)
> -			return -EIOCBQUEUED;
> +			return ERR_PTR(-EIOCBQUEUED);
>   
>   		for (;;) {
>   			set_current_state(TASK_UNINTERRUPTIBLE);
> @@ -574,10 +575,25 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>   		__set_current_state(TASK_RUNNING);
>   	}
>   
> -	return iomap_dio_complete(dio);
> +	return dio;
>   
>   out_free_dio:
>   	kfree(dio);
> -	return ret;
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL_GPL(__iomap_dio_rw);
> +
> +ssize_t
> +iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> +		const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
> +		bool wait_for_completion)
> +{
> +	struct iomap_dio *dio;
> +
> +	dio = __iomap_dio_rw(iocb, iter, ops, dops, wait_for_completion);
> +	if (IS_ERR_OR_NULL(dio))
> +		return PTR_ERR_OR_ZERO(dio);
> +	return iomap_dio_complete(dio);
>   }
>   EXPORT_SYMBOL_GPL(iomap_dio_rw);
> +

Got an extra + here for some reason.  Otherwise

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef