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d06923670b
The nvme keep-alive operation, which executes at a periodic interval,
could potentially sneak in while shutting down a fabric controller.
This may lead to a race between the fabric controller admin queue
destroy code path (invoked while shutting down controller) and hw/hctx
queue dispatcher called from the nvme keep-alive async request queuing
operation. This race could lead to the kernel crash shown below:
Call Trace:
autoremove_wake_function+0x0/0xbc (unreliable)
__blk_mq_sched_dispatch_requests+0x114/0x24c
blk_mq_sched_dispatch_requests+0x44/0x84
blk_mq_run_hw_queue+0x140/0x220
nvme_keep_alive_work+0xc8/0x19c [nvme_core]
process_one_work+0x200/0x4e0
worker_thread+0x340/0x504
kthread+0x138/0x140
start_kernel_thread+0x14/0x18
While shutting down fabric controller, if nvme keep-alive request sneaks
in then it would be flushed off. The nvme_keep_alive_end_io function is
then invoked to handle the end of the keep-alive operation which
decrements the admin->q_usage_counter and assuming this is the last/only
request in the admin queue then the admin->q_usage_counter becomes zero.
If that happens then blk-mq destroy queue operation (blk_mq_destroy_
queue()) which could be potentially running simultaneously on another
cpu (as this is the controller shutdown code path) would forward
progress and deletes the admin queue. So, now from this point onward
we are not supposed to access the admin queue resources. However the
issue here's that the nvme keep-alive thread running hw/hctx queue
dispatch operation hasn't yet finished its work and so it could still
potentially access the admin queue resource while the admin queue had
been already deleted and that causes the above crash.
This fix helps avoid the observed crash by implementing keep-alive as a
synchronous operation so that we decrement admin->q_usage_counter only
after keep-alive command finished its execution and returns the command
status back up to its caller (blk_execute_rq()). This would ensure that
fabric shutdown code path doesn't destroy the fabric admin queue until
keep-alive request finished execution and also keep-alive thread is not
running hw/hctx queue dispatch operation.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
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 reStructuredText 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.