[Sheepdog] [PATCH] object_cache: fix a race condition

[Liu Yuan]

On 04/28/2012 09:35 PM, Liu Yuan wrote:

> From: Liu Yuan <tailai.ly at taobao.com>
> 
> create_cache_object() need to get a lock to avoid race with
> object_cache_rw().
> 
> This is to address below bug in the log:
> Apr 28 17:48:12 do_io_request(931) 2, 47c33f00003f80 , 1
> Apr 28 17:48:12 object_cache_rw(321) 00003f80, len 4096, off 1396736
> Apr 28 17:48:12 client_rx_handler(427) HEAD, fd:280
> Apr 28 17:48:12 client_rx_handler(432) DATA_INIT, fd:280
> Apr 28 17:48:12 client_rx_handler(470) END, fd:280
> Apr 28 17:48:12 queue_request(275) 2
> Apr 28 17:48:12 do_io_request(931) 2, b1f0b000003f9b , 1
> Apr 28 17:48:12 object_cache_pull(423) [local] 00003f9b
> Apr 28 17:48:12 object_cache_pull(423) [local] 00003f9b
> Apr 28 17:48:12 create_cache_object(352) 00003f9b already created
> Apr 28 17:48:12 object_cache_rw(321) 00003f9b, len 16384, off 2940928
> Apr 28 17:48:12 read_cache_object(307) size =0; count= 16384
> Apr 28 17:48:12 do_io_request(956) failed: 2, b1f0b000003f9b , 1, 3
> Apr 28 17:48:12 io_op_done(151) leaving sheepdog cluster
> 
> Signed-off-by: Liu Yuan <tailai.ly at taobao.com>
> ---
>  sheep/object_cache.c |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/sheep/object_cache.c b/sheep/object_cache.c
> index a1b9e2a..0d00bb1 100644
> --- a/sheep/object_cache.c
> +++ b/sheep/object_cache.c
> @@ -350,12 +350,22 @@ static int create_cache_object(struct object_cache *oc, uint32_t idx, void *buff
>  		ret = SD_RES_EIO;
>  		goto out;
>  	}
> +	if (flock(fd, LOCK_EX) < 0) {
> +		ret = SD_RES_EIO;
> +		eprintf("%m\n");
> +		goto out_close;
> +	}
>  	ret = xpwrite(fd, buffer, buf_size, 0);
>  	if (ret != buf_size) {
>  		ret = SD_RES_EIO;
>  		eprintf("failed, vid %"PRIx32", idx %"PRIx32"\n", oc->vid, idx);
>  		goto out_close;
>  	}
> +	if (flock(fd, LOCK_UN) < 0) {
> +		ret = SD_RES_EIO;
> +		eprintf("%m\n");
> +		goto out_close;
> +	}
>  
>  	ret = SD_RES_SUCCESS;
>  	dprintf("%08"PRIx32" size %zu\n", idx, buf_size);


Applied.

Thanks,
Yuan