Re: [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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