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SubjectRe: [PATCH v2 04/10] block: revert back to synchronous request_queue removal
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On 4/19/20 12:45 PM, Luis Chamberlain wrote:
> +/**
> + * blk_put_queue - decrement the request_queue refcount
> + *
> + * @q: the request_queue structure to decrement the refcount for
> + *

How about following the example from
Documentation/doc-guide/kernel-doc.rst and not leaving a blank line
above the function argument documentation?

> + * Decrements the refcount to the request_queue kobject, when this reaches
^^
of?
> + * 0 we'll have blk_release_queue() called. You should avoid calling
> + * this function in atomic context but if you really have to ensure you
> + * first refcount the block device with bdgrab() / bdput() so that the
> + * last decrement happens in blk_cleanup_queue().
> + */

Is calling bdgrab() and bdput() an option from a context in which it is
not guaranteed that the block device is open?

Does every context that calls blk_put_queue() also call blk_cleanup_queue()?

How about avoiding confusion by changing the last sentence of that
comment into something like the following: "The last reference must not
be dropped from atomic context. If it is necessary to call
blk_put_queue() from atomic context, make sure that that call does not
decrease the request queue refcount to zero."

> /**
> * blk_cleanup_queue - shutdown a request queue
> + *
> * @q: request queue to shutdown
> *

How about following the example from
Documentation/doc-guide/kernel-doc.rst and not leaving a blank line
above the function argument documentation?

> * Mark @q DYING, drain all pending requests, mark @q DEAD, destroy and
> * put it. All future requests will be failed immediately with -ENODEV.
> + *
> + * You should not call this function in atomic context. If you need to
> + * refcount a request_queue in atomic context, instead refcount the
> + * block device with bdgrab() / bdput().

Surrounding blk_cleanup_queue() with bdgrab() / bdput() does not help.
This blk_cleanup_queue() must not be called from atomic context.

> /**
> - * __blk_release_queue - release a request queue
> - * @work: pointer to the release_work member of the request queue to be released
> + * blk_release_queue - release a request queue
> + *
> + * This function is called as part of the process when a block device is being
> + * unregistered. Releasing a request queue starts with blk_cleanup_queue(),
> + * which set the appropriate flags and then calls blk_put_queue() as the last
> + * step. blk_put_queue() decrements the reference counter of the request queue
> + * and once the reference counter reaches zero, this function is called to
> + * release all allocated resources of the request queue.
> *
> - * Description:
> - * This function is called when a block device is being unregistered. The
> - * process of releasing a request queue starts with blk_cleanup_queue, which
> - * set the appropriate flags and then calls blk_put_queue, that decrements
> - * the reference counter of the request queue. Once the reference counter
> - * of the request queue reaches zero, blk_release_queue is called to release
> - * all allocated resources of the request queue.
> + * This function can sleep, and so we must ensure that the very last
> + * blk_put_queue() is never called from atomic context.
> + *
> + * @kobj: pointer to a kobject, who's container is a request_queue
> */

Please follow the style used elsewhere in the kernel and move function
argument documentation just below the line with the function name.

Thanks,

Bart.

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