From: Hannes Reinecke <hare@suse.de>
To: Luis Chamberlain <mcgrof@kernel.org>, axboe@kernel.dk
Cc: bvanassche@acm.org, ming.lei@redhat.com, hch@infradead.org,
jack@suse.cz, osandov@fb.com, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/8] block: refcount the request_queue early in __device_add_disk()
Date: Wed, 12 May 2021 17:07:54 +0200 [thread overview]
Message-ID: <ae439ba5-ad0e-f898-8eda-9c5533af58f8@suse.de> (raw)
In-Reply-To: <20210512064629.13899-2-mcgrof@kernel.org>
On 5/12/21 8:46 AM, Luis Chamberlain wrote:
> We refcount the request_queue right now towards the end of the
> __device_add_disk(), however when we add error handling on this
> function we'll want to refcount the request_queue first, to help
> make less complicated changes on drivers on their error paths.
>
> For instance, today a driver may call add_disk without error handling
> but still handle other errors:
>
> int foo_block_add(...)
> {
> ...
> queue = blk_mq_init_queue(...);
> ...
> disk->queue = queue;
> disk = alloc_disk(...);
> if (!disk)
> goto out_free_queue;
> ...
> add_disk(disk);
> ...
> return 0;
>
> out_free_queue:
> blk_cleanup_queue(queue);
> /* Note: we never call put_disk() as add_disk() never failed */
> ...
> }
>
> We want drivers to cleanup with put_disk() on the error path if
> add_disk() fails. However, calling blk_cleanup_queue() will already
> put the queue, and so the last put_disk() on the error path will
> be extra. This can be simplified later if once error handling is
> added to __device_add_disk(), if refcounting the request_queue
> fails right away on __device_add_disk() we just return early and
> set disk->NULL for the driver. That would ensure driver error
> paths chug on with their error paths, and all they'd need to
> expand with is the missing put_disk().
>
> The collateral evolution for adding error paths for add_disk() becomes
> larger with the alternative of replacing the blk_cleanup_queue() with
> a put_disk(). We'd still need to sprinkle then some blk_cleanup_queue()
> calls on the driver paths up above prior to add_disk(). And how would
> we know we reached a part of add_disk() which did refcount then?
>
> A related commit is 5a0ec388ef0 ("pktcdvd: Fix pkt_setup_dev() error
> path") which *had* to take the approach of removing the blk_cleanup_queue()
> because otherwise the driver crashes.
>
> Moving this to the top ensure our future error path can easily just
> handle this itself. For instance, if it was not able to refcount the
> request_queue it can disk->queue to NULL, that way allowing a
> blk_cleanup_queue() call followed but a put_disk(). And if the
> refcount was incremented, we'd still be able to keep the same error
> path of blk_cleanup_queue() followed by put_disk().
>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
> block/genhd.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
next prev parent reply other threads:[~2021-05-12 15:10 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 6:46 [PATCH v1 0/8] block: add error handling for *add_disk*() Luis Chamberlain
2021-05-12 6:46 ` [PATCH v1 1/8] block: refcount the request_queue early in __device_add_disk() Luis Chamberlain
2021-05-12 15:07 ` Hannes Reinecke [this message]
2021-05-12 6:46 ` [PATCH v1 2/8] block: move disk announce work from register_disk() to a helper Luis Chamberlain
2021-05-12 15:08 ` Hannes Reinecke
2021-05-12 6:46 ` [PATCH v1 3/8] block: move disk invalidation from del_gendisk() into " Luis Chamberlain
2021-05-12 15:09 ` Hannes Reinecke
2021-05-12 6:46 ` [PATCH v1 4/8] block: move disk unregistration work from del_gendisk() to " Luis Chamberlain
2021-05-12 15:09 ` Hannes Reinecke
2021-05-12 6:46 ` [PATCH v1 5/8] block: add initial error handling for *add_disk()* and friends Luis Chamberlain
2021-05-12 15:15 ` Hannes Reinecke
2021-05-12 6:46 ` [PATCH v1 6/8] loop: add error handling support for add_disk() Luis Chamberlain
2021-05-12 15:15 ` Hannes Reinecke
2021-05-12 6:46 ` [PATCH v1 7/8] null_blk: " Luis Chamberlain
2021-05-12 15:16 ` Hannes Reinecke
2021-05-12 16:47 ` Luis Chamberlain
2021-05-12 17:12 ` Hannes Reinecke
2021-05-12 17:20 ` Luis Chamberlain
2021-05-12 17:28 ` Hannes Reinecke
2021-05-19 19:57 ` Luis Chamberlain
2021-05-12 6:46 ` [PATCH v1 8/8] block: add add_disk() failure injection support Luis Chamberlain
2021-05-12 15:22 ` Hannes Reinecke
2021-05-12 16:56 ` Luis Chamberlain
2021-05-12 17:55 ` Hannes Reinecke
2021-05-12 14:44 ` [PATCH v1 0/8] block: add error handling for *add_disk*() Christoph Hellwig
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