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From: Ammar Faizi <[email protected]>
To: Keith Busch <[email protected]>
Cc: Facebook Kernel Team <[email protected]>,
	Jens Axboe <[email protected]>, Christoph Hellwig <[email protected]>,
	Al Viro <[email protected]>,
	Keith Busch <[email protected]>,
	Fernanda Ma'rouf <[email protected]>,
	io-uring Mailing List <[email protected]>,
	Linux Block Mailing List <[email protected]>,
	Linux fsdevel Mailing List <[email protected]>,
	Linux NVME Mailing List <[email protected]>
Subject: Re: [PATCHv2 6/7] io_uring: add support for dma pre-mapping
Date: Wed, 3 Aug 2022 06:25:14 +0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 8/3/22 2:36 AM, Keith Busch wrote:
> From: Keith Busch <[email protected]>
> 
> Provide a new register operation that can request to pre-map a known
> bvec to the requested fixed file's specific implementation. If
> successful, io_uring will use the returned dma tag for future fixed
> buffer requests to the same file.
> 
> Signed-off-by: Keith Busch <[email protected]>
[...]
> +static int io_register_map_buffers(struct io_ring_ctx *ctx, void __user *arg)
> +{
> +	struct io_uring_map_buffers map;
> +	struct io_fixed_file *file_slot;
> +	struct file *file;
> +	int ret, i;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	ret = get_map_range(ctx, &map, arg);
> +	if (ret < 0)
> +		return ret;
> +
> +	file_slot = io_fixed_file_slot(&ctx->file_table,
> +			array_index_nospec(map.fd, ctx->nr_user_files));
> +	if (!file_slot || !file_slot->file_ptr)
> +		return -EBADF;

The @file_slot NULL-check doesn't make sense. The definition of
io_fixed_file_slot() is:

static inline struct io_fixed_file *
io_fixed_file_slot(struct io_file_table *table, unsigned i)
{
         return &table->files[i];
}

which takes the address of an element in the array. So @file_slot
should never be NULL, if it ever be, something has gone wrong.

If you ever had @ctx->file_table.files being NULL in this path, you
should NULL-check the @->files itself, *not* the return value of
io_fixed_file_slot().

IOW:

...
	// NULL check here.
         if (!ctx->file_table.files)
                 return -EBADF;

         file_slot = io_fixed_file_slot(&ctx->file_table,
                                        array_index_nospec(map.fd, ctx->nr_user_files));
         if (!file_slot->file_ptr)
                 return -EBADF;
...

>   	for (i = 0; i < ctx->nr_user_files; i++) {
> -		struct file *file = io_file_from_index(&ctx->file_table, i);
> +		struct io_fixed_file *f = io_fixed_file_slot(&ctx->file_table, i);
> +		struct file *file;
>   
> -		if (!file)
> +		if (!f)
>   			continue;

The same thing, this @f NULL-check is not needed.

> -		if (io_fixed_file_slot(&ctx->file_table, i)->file_ptr & FFS_SCM)
> +		if (f->file_ptr & FFS_SCM)
>   			continue;
> +
> +		io_dma_unmap_file(ctx, f);
> +		file = io_file_from_fixed(f);
>   		io_file_bitmap_clear(&ctx->file_table, i);
>   		fput(file);
>   	}

-- 
Ammar Faizi

  reply	other threads:[~2022-08-02 23:25 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-02 19:36 [PATCHv2 0/7] dma mapping optimisations Keith Busch
2022-08-02 19:36 ` [PATCHv2 1/7] blk-mq: add ops to dma map bvec Keith Busch
2022-08-02 19:36 ` [PATCHv2 2/7] file: " Keith Busch
2022-08-02 19:36 ` [PATCHv2 3/7] iov_iter: introduce type for preregistered dma tags Keith Busch
2022-08-02 19:36 ` [PATCHv2 4/7] block: add dma tag bio type Keith Busch
2022-08-02 19:36 ` [PATCHv2 5/7] io_uring: introduce file slot release helper Keith Busch
2022-08-02 19:36 ` [PATCHv2 6/7] io_uring: add support for dma pre-mapping Keith Busch
2022-08-02 23:25   ` Ammar Faizi [this message]
2022-08-02 19:36 ` [PATCHv2 7/7] nvme-pci: implement dma_map support Keith Busch
2022-08-03 20:52 ` [PATCHv2 0/7] dma mapping optimisations Jens Axboe
2022-08-04 16:28   ` Keith Busch
2022-08-04 16:42     ` Jens Axboe

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