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The deadlock combines 4 flows in parallel:
- ns scanning (triggered from reconnect)
- request timeout
- ANA update (triggered from reconnect)
- I/O coming into the mpath device
(1) ns scanning triggers disk revalidation -> update disk info ->
freeze queue -> but blocked, due to (2)
(2) timeout handler reference the g_usage_counter - > but blocks in
the transport .timeout() handler, due to (3)
(3) the transport timeout handler (indirectly) calls nvme_stop_queue() ->
which takes the (down_read) namespaces_rwsem - > but blocks, due to (4)
(4) ANA update takes the (down_write) namespaces_rwsem -> calls
nvme_mpath_set_live() -> which synchronize the ns_head srcu
(see commit 504db087aa) -> but blocks, due to (5)
(5) I/O came into nvme_mpath_make_request -> took srcu_read_lock ->
direct_make_request > blk_queue_enter -> but blocked, due to (1)
==> the request queue is under freeze -> deadlock.
The fix is making ANA update take a read lock as the namespaces list
is not manipulated, it is just the ns and ns->head that are being
updated (which is protected with the ns->head lock).
Fixes: 0d0b660f21 ("nvme: add ANA support")
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
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.