On Sat, Aug 3, 2024 at 9:54 AM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
On Sat, Aug 03, 2024 at 05:48:14AM +0530, Riyan Dhiman wrote:
> Adhere to Linux kernel coding style
>
> Reported by checkpatch:
>
> CHECK: mutex definition without comment
>
> Proof for comment:
>
> 1. The mutex is used to protect access to the 'running' list
> (line 1798 tsi148_dma_list_exec function)
> mutex_lock(&ctrlrl->mtx);
> if (!list_empty(&ctrlr->running)) {
> mutex_unlock(&ctrlr->mtx);
> return -EBUSY;
> }
Why did you chop out the "channel = ctrlr->number;" line? That code
looks like this:
I included only the mutex lock and unlock part of the code in the message.
I thought adding the entire code snippet would make the commit message too lengthy.
drivers/staging/vme_user/vme_tsi148.c
1798 mutex_lock(&ctrlr->mtx);
1799
1800 channel = ctrlr->number;
1801
1802 if (!list_empty(&ctrlr->running)) {
1803 /*
1804 * XXX We have an active DMA transfer and currently haven't
1805 * sorted out the mechanism for "pending" DMA transfers.
1806 * Return busy.
1807 */
1808 /* Need to add to pending here */
1809 mutex_unlock(&ctrlr->mtx);
1810 return -EBUSY;
1811 }
1812
1813 list_add(&list->list, &ctrlr->running);
The first line after we take a lock and the last line before we drop
the lock are hopefully chosen because they need to be protected by the
lock.
Yes, I included only that part of the code in the commit message to avoid a lengthy commit message
> 2. It's also used when removing DMA list from running list:
> (line 1862 tsi148_dma_list_exec function)
> mutex_lock(&ctrlr->mtx);
> list_del(&list->list);
> mutex_unlock(&ctrlr->mtx);
> Ensuring thread-safe modification of the controller's state.
>
> Without this mutex, concurrent access to the DMA controller's state could
> lead to data corruption or inconsistant state.
>
It's also used in drivers/staging/vme_user/vme.c
What you should do is rename the mutex from mtx to XXX_mtx and then
rename all the places where it is used. Keep renaming until the driver
builds.
XXX_mtx is obviously not the correct name. But "mtx" is vague and
useless. There are 3 other locks in this header file which have the
same name so not only is it useless as a descriptive name, it's also
useless for searching.
Yes, I agree 'mt' is a vague name and doesn't convey much information.
In this patch, I have added only comments to address the checkpatch error.
Given your suggestion to change the variable name, I'd like to confirm,
Should I create a new patch that includes both the comment and the 'mtx' variable name change?
Or should I leave this current patch with comments only and
create a separate patch for the variable name changes?
Since you say that it is "protect access to the 'running' list", then
that means you need to check all the places where the running list is
accessed and ensure that the lock is held. Or if it's not, what makes
that thread safe?
Yes, I have checked the lock usage in all the places where the 'running' list is accessed.
> diff --git a/drivers/staging/vme_user/vme_bridge.h b/drivers/staging/vme_user/vme_bridge.h
> index 9bdc41bb6602..bb3750b40eb1 100644
> --- a/drivers/staging/vme_user/vme_bridge.h
> +++ b/drivers/staging/vme_user/vme_bridge.h
> @@ -61,6 +61,7 @@ struct vme_dma_list {
> struct vme_dma_resource {
> struct list_head list;
> struct vme_bridge *parent;
> + /* Mutex to protect DMA controller resources and ensure thread-safe operations */
"resources" is too vague. "ensure thread-safe operations" is obvious
and doesn't need to be said.
Should I mention the exact resources this mutex protects?
Regards,
Riyan Dhiman
