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From:   Mitchell Levy via B4 Relay 
        <devnull+levymitchell0.gmail.com@kernel.org>
Subject: [PATCH RFC 0/2] hyperv: Use raw_spinlock_t when not sleepable
Date:   Wed, 09 Aug 2023 22:36:31 +0000
Message-Id: <20230809-b4-rt_preempt-fix-v1-0-7283bbdc8b14@gmail.com>
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To:     "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= <kw@linux.com>,
        Rob Herring <robh@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>
Cc:     linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-pci@vger.kernel.org, Mitchell Levy <levymitchell0@gmail.com>
Reply-To: <levymitchell0@gmail.com>
Precedence: bulk

When compiled with PREEMPT_RT, spinlock_t is sleepable. While I did not
observe this causing any lockups on my system, it did cause warnings to
be emitted when compiled with lock debugging. This series fixes some
instances where spinlock_t is used in non-sleepable contexts, though it
almost certainly does not find every such instance.

An example of the warning raised by lockdep:
=============================
[BUG: Invalid wait context ]
6.5.0-rc1+ #16 Not tainted
-----------------------------
swapper/0/1 is trying to lock:
ffffa05a014d64c0 (&channel→sched_lock) {...}-{3:3}, at: vmbus_isr+0x179/0x320
other info that might help us debug this:
context-{2:2}
2 locks held by swapper/0/1:
 #0: ffffffff909a9c70 (misc_mtx){+.+.}-{4:4}, at: misc_register+0x34/0x180
 #1: ffffffff9079b4c8 (rcu_read_lock) {...}-{1:3}, at: rcu_lock_acquire+0x0/0x40
stack backtrace:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc1+ #16
Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 05/09/2022

Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
---
Mitchell Levy (2):
      Use raw_spinlock_t for vmbus_channel.sched_lock
      Use raw_spinlock_t in vmbus_requestor

 drivers/hv/channel.c                | 6 +++---
 drivers/hv/channel_mgmt.c           | 2 +-
 drivers/hv/vmbus_drv.c              | 4 ++--
 drivers/pci/controller/pci-hyperv.c | 6 +++---
 include/linux/hyperv.h              | 8 ++++----
 5 files changed, 13 insertions(+), 13 deletions(-)
---
base-commit: 14f9643dc90adea074a0ffb7a17d337eafc6a5cc
change-id: 20230807-b4-rt_preempt-fix-35a65c90c6c9

Best regards,
-- 
Mitchell Levy <levymitchell0@gmail.com>