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From:   Benjamin Bara <bbara93@gmail.com>
Date:   Sat, 15 Jul 2023 09:53:24 +0200
Subject: [PATCH v7 2/5] i2c: core: run atomic i2c xfer when !preemptible
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Message-Id: <20230327-tegra-pmic-reboot-v7-2-18699d5dcd76@skidata.com>
References: <20230327-tegra-pmic-reboot-v7-0-18699d5dcd76@skidata.com>
In-Reply-To: <20230327-tegra-pmic-reboot-v7-0-18699d5dcd76@skidata.com>
To:     Wolfram Sang <wsa@kernel.org>, Lee Jones <lee@kernel.org>,
        rafael.j.wysocki@intel.com,
        Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc:     dmitry.osipenko@collabora.com, peterz@infradead.org,
        jonathanh@nvidia.com, richard.leitner@linux.dev,
        treding@nvidia.com, linux-kernel@vger.kernel.org,
        linux-i2c@vger.kernel.org, linux-tegra@vger.kernel.org,
        Benjamin Bara <benjamin.bara@skidata.com>,
        stable@vger.kernel.org, Nishanth Menon <nm@ti.com>
Precedence: bulk

From: Benjamin Bara <benjamin.bara@skidata.com>

Since bae1d3a05a8b, i2c transfers are non-atomic if preemption is
disabled. However, non-atomic i2c transfers require preemption (e.g. in
wait_for_completion() while waiting for the DMA).

panic() calls preempt_disable_notrace() before calling
emergency_restart(). Therefore, if an i2c device is used for the
restart, the xfer should be atomic. This avoids warnings like:

[   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
[   12.676926] Voluntary context switch within RCU read-side critical section!
...
[   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
[   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
...
[   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
[   13.001050]  machine_restart from panic+0x2a8/0x32c

Use !preemptible() instead, which is basically the same check as
pre-v5.2.

Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
Cc: stable@vger.kernel.org # v5.2+
Suggested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Acked-by: Wolfram Sang <wsa@kernel.org>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
---
 drivers/i2c/i2c-core.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-core.h b/drivers/i2c/i2c-core.h
index 1247e6e6e975..05b8b8dfa9bd 100644
--- a/drivers/i2c/i2c-core.h
+++ b/drivers/i2c/i2c-core.h
@@ -29,7 +29,7 @@ int i2c_dev_irq_from_resources(const struct resource *resources,
  */
 static inline bool i2c_in_atomic_xfer_mode(void)
 {
-	return system_state > SYSTEM_RUNNING && irqs_disabled();
+	return system_state > SYSTEM_RUNNING && !preemptible();
 }
 
 static inline int __i2c_lock_bus_helper(struct i2c_adapter *adap)

-- 
2.34.1