Re: [PATCH] vmcore-dmesg: fix infinite loop if log buffer wraps around

[Baoquan He <bhe@redhat.com>]

On 05/23/18 at 01:59pm, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> We hit a bug where vmcore-dmesg would get stuck in a loop, and since we
> were redirecting the output to a file, it wouldn't stop until it filled
> up the disk. This only happened when the dmesg buffer had filled up and
> wrapped around. It turns out that when we hit the end of the buffer, we
> are looping back to the first record instead of the beginning of the
> buffer, which will always loop forever.
> 
> Fixes: e08d26b3b7f1 ("vmcore-dmesg: avoid allocating large memory chunk for log buf")
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---
>  vmcore-dmesg/vmcore-dmesg.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/vmcore-dmesg/vmcore-dmesg.c b/vmcore-dmesg/vmcore-dmesg.c
> index e340ef4..7972788 100644
> --- a/vmcore-dmesg/vmcore-dmesg.c
> +++ b/vmcore-dmesg/vmcore-dmesg.c
> @@ -689,7 +689,7 @@ static void dump_dmesg_structured(int fd)
>  		 */
>  		loglen = struct_val_u16(buf, log_offset_len);
>  		if (!loglen)
> -			current_idx = log_first_idx;
> +			current_idx = 0;

Looks like a good fix, ack it.

Acked-by: Baoquan He <bhe@redhat.com>

Strange it isn't found until now, the case which log_next_idx is before
log_first_idx sholdn't be seen rarely.


Thanks
Baoquan


>  		else
>  			/* Move to next record */
>  			current_idx += loglen;
> -- 
> 2.9.5
> 
> 
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