Re: [PATCH 1/4] io_uring: track fixed files with a bitmap

[Hao Xu <haoxu.linux@xxxxxxxxx>]

在 2022/5/9 上午7:49, Jens Axboe 写道:
> In preparation for adding a basic allocator for direct descriptors,
> add helpers that set/clear whether a file slot is used.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
>   fs/io_uring.c | 37 +++++++++++++++++++++++++++++++++++--
>   1 file changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index b6d491c9a25f..6eac6629e7d4 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -257,6 +257,7 @@ struct io_rsrc_put {
>   
>   struct io_file_table {
>   	struct io_fixed_file *files;
> +	unsigned long *bitmap;
>   };
>   
>   struct io_rsrc_node {
> @@ -7573,6 +7574,7 @@ static inline struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
>   	/* mask in overlapping REQ_F and FFS bits */
>   	req->flags |= (file_ptr << REQ_F_SUPPORT_NOWAIT_BIT);
>   	io_req_set_rsrc_node(req, ctx, 0);
> +	WARN_ON_ONCE(file && !test_bit(fd, ctx->file_table.bitmap));
>   out:
>   	io_ring_submit_unlock(ctx, issue_flags);
>   	return file;
> @@ -8639,13 +8641,35 @@ static bool io_alloc_file_tables(struct io_file_table *table, unsigned nr_files)
>   {
>   	table->files = kvcalloc(nr_files, sizeof(table->files[0]),
>   				GFP_KERNEL_ACCOUNT);
> -	return !!table->files;
> +	if (unlikely(!table->files))
> +		return false;
> +
> +	table->bitmap = bitmap_zalloc(nr_files, GFP_KERNEL_ACCOUNT);
> +	if (unlikely(!table->bitmap)) {
> +		kvfree(table->files);
> +		return false;
> +	}
> +
> +	return true;
>   }
>   
>   static void io_free_file_tables(struct io_file_table *table)
>   {
>   	kvfree(table->files);
> +	bitmap_free(table->bitmap);
>   	table->files = NULL;
> +	table->bitmap = NULL;
> +}
> +
> +static inline void io_file_bitmap_set(struct io_file_table *table, int bit)
> +{
> +	WARN_ON_ONCE(test_bit(bit, table->bitmap));
> +	__set_bit(bit, table->bitmap);
> +}
> +
> +static inline void io_file_bitmap_clear(struct io_file_table *table, int bit)
> +{
> +	__clear_bit(bit, table->bitmap);
>   }
>   
>   static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
> @@ -8660,6 +8684,7 @@ static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
>   			continue;
>   		if (io_fixed_file_slot(&ctx->file_table, i)->file_ptr & FFS_SCM)
>   			continue;
> +		io_file_bitmap_clear(&ctx->file_table, i);
>   		fput(file);
>   	}
>   #endif
> @@ -9063,6 +9088,7 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
>   		}
>   		file_slot = io_fixed_file_slot(&ctx->file_table, i);
>   		io_fixed_file_set(file_slot, file);
> +		io_file_bitmap_set(&ctx->file_table, i);
>   	}
>   
>   	io_rsrc_node_switch(ctx, NULL);
> @@ -9123,6 +9149,7 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
>   		if (ret)
>   			goto err;
>   		file_slot->file_ptr = 0;
> +		io_file_bitmap_clear(&ctx->file_table, slot_index);
>   		needs_switch = true;
>   	}
>   
> @@ -9130,13 +9157,16 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
>   	if (!ret) {
>   		*io_get_tag_slot(ctx->file_data, slot_index) = 0;
>   		io_fixed_file_set(file_slot, file);
> +		io_file_bitmap_set(&ctx->file_table, slot_index);
[1]
>   	}
>   err:
>   	if (needs_switch)
>   		io_rsrc_node_switch(ctx, ctx->file_data);
>   	io_ring_submit_unlock(ctx, issue_flags);
> -	if (ret)
> +	if (ret) {
> +		io_file_bitmap_clear(&ctx->file_table, slot_index);
We don't need to clean it, since we get here only when we didn't
run [1], which means we haven't set it.

>   		fput(file);
> +	}
>   	return ret;
>   }
>