On Sun, Apr 19, 2020 at 03:23:31PM -0700, Bart Van Assche wrote: > 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? Sure. > > + * 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? If the block device is not open, nope. For that blk_get_queue() can be used, and is used by the block layer. This begs the question: Do we have *drivers* which requires access to the request_queue from atomic context when the block device is not open? > Does every context that calls blk_put_queue() also call blk_cleanup_queue()? Nope. > 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." This would be fine, if not for the fact that it seems worthy to also ask ourselves if we even need blk_get_queue() / blk_put_queue() exported for drivers. I haven't yet finalized my review of this, but planting the above comment cements the idea further that it is possible. Granted, I think its fine as -- that is our current use case and best practice. Removing the export for blk_get_queue() / blk_put_queue() should entail reviewing each driver caller and ensuring that it is not needed. And that is not done yet, and should be considered a separate effort. > > /** > > * 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? Will do. > > * 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. I'll just remove that. > > > /** > > - * __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. Sure, thanks for the review. Luis
