Re: [PATCH] aio: Fix freeze protection of aio writes

[Benjamin LaHaise <bcrl@kvack.org>]

On Thu, Jan 07, 2016 at 04:03:04PM +0100, Jan Kara wrote:
> Currently we dropped freeze protection of aio writes just after IO was
> submitted. Thus aio write could be in flight while the filesystem was
> frozen and that could result in unexpected situation like aio completion
> wanting to convert extent type on frozen filesystem. Testcase from
> Dmitry triggering this is like:
> 
> for ((i=0;i<60;i++));do fsfreeze -f /mnt ;sleep 1;fsfreeze -u /mnt;done &
> fio --bs=4k --ioengine=libaio --iodepth=128 --size=1g --direct=1 \
>     --runtime=60 --filename=/mnt/file --name=rand-write --rw=randwrite
> 
> Fix the problem by dropping freeze protection only once IO is completed
> in aio_complete().

Why isn't this code placed in file_start_write() and file_end_write()?  
That makes more sense to me than sprinkling it in the aio code.

		-ben

> Reported-by: Dmitry Monakhov <dmonakhov@openvz.org>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/aio.c           | 31 ++++++++++++++++++++++++++++---
>  include/linux/fs.h |  1 +
>  2 files changed, 29 insertions(+), 3 deletions(-)
> 
> This patch seems to have fallen through the cracks. Al / Ben, can you please
> merge it? Thanks!
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index 155f84253f33..ee0871cb4677 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1065,6 +1065,19 @@ static void aio_complete(struct kiocb *kiocb, long res, long res2)
>  	unsigned tail, pos, head;
>  	unsigned long	flags;
>  
> +	if (kiocb->ki_flags & IOCB_WRITE) {
> +		struct file *f = kiocb->ki_filp;
> +
> +		/*
> +		 * Tell lockdep we inherited freeze protection from submission
> +		 * thread.
> +		 */
> +		percpu_rwsem_acquire(
> +			&f->f_inode->i_sb->s_writers.rw_sem[SB_FREEZE_WRITE-1],
> +			1, _THIS_IP_);
> +		file_end_write(f);
> +	}
> +
>  	/*
>  	 * Special case handling for sync iocbs:
>  	 *  - events go directly into the iocb for fast handling
> @@ -1449,13 +1462,25 @@ rw_common:
>  
>  		len = ret;
>  
> -		if (rw == WRITE)
> +		if (rw == WRITE) {
>  			file_start_write(file);
> +			req->ki_flags |= IOCB_WRITE;
> +		}
>  
>  		ret = iter_op(req, &iter);
>  
> -		if (rw == WRITE)
> -			file_end_write(file);
> +		if (rw == WRITE) {
> +			/*
> +			 * 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.
> +			 */
> +			percpu_rwsem_release(
> +				&file->f_inode->i_sb->s_writers.rw_sem[SB_FREEZE_WRITE-1],
> +				1, _THIS_IP_);
> +		}
> +
>  		kfree(iovec);
>  		break;
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3aa514254161..54af40ed6a26 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -319,6 +319,7 @@ struct writeback_control;
>  #define IOCB_EVENTFD		(1 << 0)
>  #define IOCB_APPEND		(1 << 1)
>  #define IOCB_DIRECT		(1 << 2)
> +#define IOCB_WRITE		(1 << 3)
>  
>  struct kiocb {
>  	struct file		*ki_filp;
> -- 
> 2.6.2

-- 
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