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[ Upstream commita77a52385e] An earlier patch which introduced smp_load_acquire/smp_store_release into rxe_queue.h incorrectly assumed that surrounding spin-locks in rxe_verbs.c around queue updates for kernel ulps was sufficient to protect the passing of data through the queues between the ulp and the rxe tasklets. But this was incorrect. The typical sequence was ulp rxe requester tasklet ------------------------ --------------------- spin_lock_irqsave() wqe = queue_head(queue) if (!queue_full(q)) { if (!wqe) spin_unlock_irqrestore return; return -ENOMEM } <process wqe> wqe = queue_producer_addr(q) <fill in wqe> queue_advance_consumer(queue) queue_advance_producer(q) spin_unlock_irqrestore() queue_head() calls queue_empty() which calls smp_load_acquire() For user space apps queue_advance_producer() calls smp_store_release() so that there is a memory barrier between the producer and the consumer but for kernel ulps queue_advance_produce() just incremented the producer index because the lock function is a release function. But to work the barrier has to come between filling in the wqe and updating the producer index. This patch adds the missing barriers. It also changes the enum names for the ulp queue types to QUEUE_TYPE_FROM/TO_ULP instead of QUEUE_TYPE_TO/FROM_DRIVER which is very ambiguous. This bug is suspected as the cause of very rare lockups in a very high scale storage application. It is a bug in any case and should be corrected. Fixes:0a67c46d2e("RDMA/rxe: Protect user space index loads/stores") Link: https://lore.kernel.org/r/20230214071053.5395-1-rpearsonhpe@gmail.com Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Signed-off-by: Sasha Levin <sashal@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 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.