Re: [f2fs-dev][PATCH] f2fs: avoid to access NULL pointer in issue_flush_thread

[Gu Zheng <guz.fnst@cn.fujitsu.com>]

Hi Yu,
Thanks for your catch.

Regards,
Gu
On 07/07/2014 09:39 AM, Chao Yu wrote:

> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=75861
> 
> Denis 2014-05-10 11:28:59 UTC reported:
> "F2FS-fs (mmcblk0p28): mounting..
>  Unable to handle kernel NULL pointer dereference at virtual address 00000018
>  ...
>  [<c0a2f678>] (_raw_spin_lock+0x3c/0x70) from [<c03a0330>] (issue_flush_thread+0x50/0x17c)
>  [<c03a0330>] (issue_flush_thread+0x50/0x17c) from [<c01b4064>] (kthread+0x98/0xa4)
>  [<c01b4064>] (kthread+0x98/0xa4) from [<c0108060>] (kernel_thread_exit+0x0/0x8)"
> 
> This patch assign cmd_control_info in sm_info before issue_flush_thread is being
> created, so this make sure that issue flush thread will have no chance to access
> invalid info in fcc.
> 
> Signed-off-by: Chao Yu <chao2.yu@samsung.com>

Reviewed-by: Gu Zheng <guz.fnst@cn.fujitsu.com>

> ---
>  fs/f2fs/segment.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index bb5980d..a4f8375 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -272,14 +272,15 @@ int create_flush_cmd_control(struct f2fs_sb_info *sbi)
>  		return -ENOMEM;
>  	spin_lock_init(&fcc->issue_lock);
>  	init_waitqueue_head(&fcc->flush_wait_queue);
> +	sbi->sm_info->cmd_control_info = fcc;
>  	fcc->f2fs_issue_flush = kthread_run(issue_flush_thread, sbi,
>  				"f2fs_flush-%u:%u", MAJOR(dev), MINOR(dev));
>  	if (IS_ERR(fcc->f2fs_issue_flush)) {
>  		err = PTR_ERR(fcc->f2fs_issue_flush);
>  		kfree(fcc);
> +		sbi->sm_info->cmd_control_info = NULL;
>  		return err;
>  	}
> -	sbi->sm_info->cmd_control_info = fcc;
>  
>  	return err;
>  }