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From: hch@lst.de (Christoph Hellwig)
Subject: [PATCH 04/47] block: provide a new BLK_EH_QUIESCED timeout return value
Date: Tue, 24 Nov 2015 16:56:09 +0100
Message-ID: <20151124155609.GA6251@lst.de> (raw)
In-Reply-To: <x491tbf2y6v.fsf@segfault.boston.devel.redhat.com>

On Tue, Nov 24, 2015@10:51:04AM -0500, Jeff Moyer wrote:
> >> 
> >> blk_complete_request:
> >> A  if (!blk_mark_rq_complete(rq) ||
> >> B      test_and_cleart_bit(REQ_ATOM_QUIESCED, &req->atomic_flags)) {
> >> C        __blk_mq_complete_request(rq);
> >> 
> >> could run alongside of:
> >> 
> >> blk_rq_check_expired:
> >> 1 if (!blk_mark_rq_complete(rq))
> >> 2   blk_rq_timed_out(rq);
> >> 
> >> So, if 1 comes before A, we have two cases to consider:
> >> 
> >> i.  the expiration path does not yet set REQ_ATOM_QUIESCED before the
> >>     completion code runs, and so the completion code does nothing.
> >
> > The command has timed out and sets REQ_ATOM_COMPLETED first,
> > the the actual completion comes in and does indeed nothing.  We now
> > set REQ_ATOM_QUIESCED and kick off a controller reset, which will
> > ultimatively complete all commands using blk_mq_complete_request.
> > Now REQ_ATOM_QUIESCED is set on the command that caused the timeout,
> > so it will be completed as well.
> >
> >> ii. the expiration path *does* SET REQ_ATOM_QUIESCED.  In this instance,
> >>     will we get yet another completion for the request when the command
> >>     is ultimately retired by the adapter reset?
> >
> > The command has timed out and sets REQ_ATOM_COMPLETED first, then
> > REQ_ATOM_QUIESCED as well.  Now the actual completion comes in and does
> > nothing because REQ_ATOM_COMPLETED was set.  We will then kick off the
> 
> See B above.  REQ_ATOM_COMPLETE is set, so the first half of that
> statement is false, but then test_and_clear_bit(REQ_ATOM_QUIESCED...)
> returns true, so we call __blk_complete_request.  So the question is,
> will we get a double completion for that request after the reset is
> performed?

We always set REQ_ATOM_COMPLETE before calling into ->timeout and thus
even having a chance to REQ_ATOM_QUIESCED.  Maybe we're talking past
each other, so if it feels like I'm off track try to explain the
race in a bit more detail.

  reply index

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-20 16:34 NVMe mega patchbomb for Linux 4.5-rc Christoph Hellwig
2015-11-20 16:34 ` [PATCH 01/47] nvme: add missing unmaps in nvme_queue_rq Christoph Hellwig
2015-11-20 16:34 ` [PATCH 02/47] block: fix blk_abort_request for blk-mq drivers Christoph Hellwig
2015-11-20 21:43   ` Jeff Moyer
2015-11-20 21:47     ` Jens Axboe
2015-11-20 21:54       ` Jeff Moyer
2015-11-20 22:20   ` Jeff Moyer
2015-11-21  7:34     ` Christoph Hellwig
2015-11-20 16:34 ` [PATCH 03/47] block: defer timeouts to a workqueue Christoph Hellwig
2015-11-23 20:31   ` Jeff Moyer
2015-11-23 20:48     ` Christoph Hellwig
2015-11-23 20:59       ` Jeff Moyer
2015-11-20 16:34 ` [PATCH 04/47] block: provide a new BLK_EH_QUIESCED timeout return value Christoph Hellwig
2015-11-24 15:16   ` Jeff Moyer
2015-11-24 15:40     ` Christoph Hellwig
2015-11-24 15:51       ` Jeff Moyer
2015-11-24 15:56         ` Christoph Hellwig [this message]
2015-11-24 16:34           ` Jeff Moyer
2015-11-24 16:47             ` Keith Busch
2015-11-24 17:56             ` Christoph Hellwig
2015-11-24 18:12               ` Jeff Moyer
2015-11-24 19:40                 ` Christoph Hellwig
2015-11-20 16:35 ` [PATCH 05/47] block: remoe REQ_ATOM_COMPLETE wrappers Christoph Hellwig
2015-11-23 21:23   ` Jeff Moyer
2015-11-24 21:22   ` Jens Axboe
2015-11-20 16:35 ` [PATCH 06/47] blk-mq: add a flags parameter to blk_mq_alloc_request Christoph Hellwig
2015-11-24 15:19   ` Jeff Moyer
2015-11-24 15:32     ` Christoph Hellwig
2015-11-24 21:21   ` Jens Axboe
2015-11-24 22:22     ` Christoph Hellwig
2015-11-24 22:25       ` Jens Axboe
2015-11-20 16:35 ` [PATCH 07/47] nvme: move struct nvme_iod to pci.c Christoph Hellwig
2015-11-20 16:35 ` [PATCH 08/47] nvme: split command submission helpers out of pci.c Christoph Hellwig
2015-11-20 16:35 ` [PATCH 09/47] nvme: add a vendor field to struct nvme_dev Christoph Hellwig
2015-11-20 16:35 ` [PATCH 10/47] nvme: use offset instead of a struct for registers Christoph Hellwig
2015-11-20 16:35 ` [PATCH 11/47] nvme: split a new struct nvme_ctrl out of struct nvme_dev Christoph Hellwig
2015-11-20 16:35 ` [PATCH 12/47] nvme: simplify nvme_setup_prps calling convention Christoph Hellwig
2015-11-20 16:35 ` [PATCH 13/47] nvme: refactor nvme_queue_rq Christoph Hellwig
2015-11-20 16:35 ` [PATCH 14/47] nvme: move nvme_error_status to common code Christoph Hellwig
2015-11-20 16:35 ` [PATCH 15/47] nvme: move nvme_setup_flush and nvme_setup_rw " Christoph Hellwig
2015-11-20 16:35 ` [PATCH 16/47] nvme: split __nvme_submit_sync_cmd Christoph Hellwig
2015-11-20 16:35 ` [PATCH 17/47] nvme: use the block layer for userspace passthrough metadata Christoph Hellwig
2015-11-20 16:35 ` [PATCH 18/47] nvme: move block_device_operations and ns/ctrl freeing to common code Christoph Hellwig
2015-11-20 16:35 ` [PATCH 19/47] nvme: add explicit quirk handling Christoph Hellwig
2015-11-20 16:35 ` [PATCH 20/47] nvme: add a common helper to read Identify Controller data Christoph Hellwig
2015-11-20 16:35 ` [PATCH 21/47] nvme: move the call to nvme_init_identify earlier Christoph Hellwig
2015-11-20 16:35 ` [PATCH 22/47] nvme: move namespace scanning to common code Christoph Hellwig
2015-11-20 16:35 ` [PATCH 23/47] nvme: move chardev and sysfs interface " Christoph Hellwig
2015-11-20 16:35 ` [PATCH 24/47] nvme: only add a controller to dev_list after it's been fully initialized Christoph Hellwig
2015-11-20 16:35 ` [PATCH 25/47] nvme: don't take the I/O queue q_lock in nvme_timeout Christoph Hellwig
2017-03-10 12:51   ` David Woodhouse
2017-03-10 14:24     ` Christoph Hellwig
2015-11-20 16:35 ` [PATCH 26/47] nvme: merge nvme_abort_req and nvme_timeout Christoph Hellwig
2015-11-20 16:35 ` [PATCH 27/47] nvme: do not restart the request timeout if we're resetting the controller Christoph Hellwig
2015-11-20 16:35 ` [PATCH 28/47] nvme: simplify resets Christoph Hellwig
2015-11-20 16:35 ` [PATCH 29/47] nvme: merge probe_work and reset_work Christoph Hellwig
2015-11-20 16:35 ` [PATCH 30/47] nvme: remove dead controllers from a work item Christoph Hellwig
2015-11-20 16:35 ` [PATCH 31/47] nvme: switch abort_limit to an atomic_t Christoph Hellwig
2015-11-20 16:35 ` [PATCH 32/47] NVMe: Implement namespace list scanning Christoph Hellwig
2015-11-20 16:35 ` [PATCH 33/47] NVMe: Use unbounded work queue for all work Christoph Hellwig
2015-11-20 16:35 ` [PATCH 34/47] NVMe: Remove device management handles on remove Christoph Hellwig
2015-11-20 16:50 ` NVMe mega patchbomb for Linux 4.5-rc Christoph Hellwig
2015-11-21  7:19 NVMe mega patchbomb for Linux 4.5-rc (resend) Christoph Hellwig
2015-11-21  7:19 ` [PATCH 04/47] block: provide a new BLK_EH_QUIESCED timeout return value Christoph Hellwig

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