Subject: Re: [PATCH, RFC 21/30] isdn: divert, hysdn: fix interruptible_sleep_on race

From: Sergei Shtylyov <[email-masked]>
Date: Thu, 02 Jan 2014 19:01:15 +0400

Hello.

On 02-01-2014 16:07, Arnd Bergmann wrote:

> These two drivers use identical code for their procfs status
> file handling, which contains a small race against status
> data becoming available while reading the file.

> This uses wait_event_interruptible instead to fix this
> particular race and eventually get rid of all sleep_on
> instances. There seems to be another race involving
> multiple concurrent readers of the same procfs file, which
> I don't try to fix here.

> Signed-off-by: Arnd Bergmann <[email-masked]>
> Cc: Karsten Keil <[email-masked]>
> Cc: [email-masked]
> ---
>   drivers/isdn/divert/divert_procfs.c | 7 ++++---
>   drivers/isdn/hysdn/hysdn_proclog.c  | 7 ++++---
>   2 files changed, 8 insertions(+), 6 deletions(-)

> diff --git a/drivers/isdn/divert/divert_procfs.c b/drivers/isdn/divert/divert_procfs.c
> index fb4f1ba..1c5dc34 100644
> --- a/drivers/isdn/divert/divert_procfs.c
> +++ b/drivers/isdn/divert/divert_procfs.c
> @@ -86,12 +86,13 @@ isdn_divert_read(struct file *file, char __user *buf, size_t count, loff_t *off)
>   	struct divert_info *inf;
>   	int len;
>
> -	if (!*((struct divert_info **) file->private_data)) {
> +	if (!(inf = *((struct divert_info **) file->private_data))) {

    checkpatch.pl shouldn't approve assignment inside *if*. Though you're 
moving it from the existing code, it wouldn't hurt to fix it.

>   		if (file->f_flags & O_NONBLOCK)
>   			return -EAGAIN;
> -		interruptible_sleep_on(&(rd_queue));
> +		wait_event_interruptible(rd_queue, (inf =
> +			*((struct divert_info **) file->private_data)));

    Parens around assignment are hardly useful.

>   	}
> -	if (!(inf = *((struct divert_info **) file->private_data)))
> +	if (!inf)
>   		return (0);
>
>   	inf->usage_cnt--;	/* new usage count */
> diff --git a/drivers/isdn/hysdn/hysdn_proclog.c b/drivers/isdn/hysdn/hysdn_proclog.c
> index b61e8d5..7b5fd8f 100644
> --- a/drivers/isdn/hysdn/hysdn_proclog.c
> +++ b/drivers/isdn/hysdn/hysdn_proclog.c
> @@ -175,14 +175,15 @@ hysdn_log_read(struct file *file, char __user *buf, size_t count, loff_t *off)
>   	int len;
>   	hysdn_card *card = PDE_DATA(file_inode(file));
>
> -	if (!*((struct log_data **) file->private_data)) {
> +	if (!(inf = *((struct log_data **) file->private_data))) {

    Here too checkpatch.pk should complain...

>   		struct procdata *pd = card->proclog;
>   		if (file->f_flags & O_NONBLOCK)
>   			return (-EAGAIN);
>
> -		interruptible_sleep_on(&(pd->rd_queue));
> +		wait_event_interruptible(pd->rd_queue, (inf =
> +				*((struct log_data **) file->private_data)));

    And parens hardly needed.

WBR, Sergei