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f5eb7e12a7
The below patches caused a regression in a multipath setup:
Fixes: 9f98772ba307 ("nvme-rdma: fix controller reset hang during traffic")
Fixes: 2875b0aecabe ("nvme-tcp: fix controller reset hang during traffic")
These patches on their own are correct because they fixed a controller reset
regression.
When we reset/teardown a controller, we must freeze and quiesce the namespaces
request queues to make sure that we safely stop inflight I/O submissions.
Freeze is mandatory because if our hctx map changed between reconnects,
blk_mq_update_nr_hw_queues will immediately attempt to freeze the queue, and
if it still has pending submissions (that are still quiesced) it will hang.
This is what the above patches fixed.
However, by freezing the namespaces request queues, and only unfreezing them
when we successfully reconnect, inflight submissions that are running
concurrently can now block grabbing the nshead srcu until either we successfully
reconnect or ctrl_loss_tmo expired (or the user explicitly disconnected).
This caused a deadlock [1] when a different controller (different path on the
same subsystem) became live (i.e. optimized/non-optimized). This is because
nvme_mpath_set_live needs to synchronize the nshead srcu before requeueing I/O
in order to make sure that current_path is visible to future (re)submisions.
However the srcu lock is taken by a blocked submission on a frozen request
queue, and we have a deadlock.
In recent kernels (v5.9+) direct_make_request was replaced by submit_bio_noacct
which does not have this issue because it bio_list will be active when
nvme-mpath calls submit_bio_noacct on the bottom device (because it was
populated when submit_bio was triggered on it.
Hence, we need to fix all the kernels that were before submit_bio_noacct was
introduced.
[1]:
Workqueue: nvme-wq nvme_tcp_reconnect_ctrl_work [nvme_tcp]
Call Trace:
__schedule+0x293/0x730
schedule+0x33/0xa0
schedule_timeout+0x1d3/0x2f0
wait_for_completion+0xba/0x140
__synchronize_srcu.part.21+0x91/0xc0
synchronize_srcu_expedited+0x27/0x30
synchronize_srcu+0xce/0xe0
nvme_mpath_set_live+0x64/0x130 [nvme_core]
nvme_update_ns_ana_state+0x2c/0x30 [nvme_core]
nvme_update_ana_state+0xcd/0xe0 [nvme_core]
nvme_parse_ana_log+0xa1/0x180 [nvme_core]
nvme_read_ana_log+0x76/0x100 [nvme_core]
nvme_mpath_init+0x122/0x180 [nvme_core]
nvme_init_identify+0x80e/0xe20 [nvme_core]
nvme_tcp_setup_ctrl+0x359/0x660 [nvme_tcp]
nvme_tcp_reconnect_ctrl_work+0x24/0x70 [nvme_tcp]
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.