[PATCH v5 2/6] i2c: core: run atomic i2c xfer when !preemptible

Benjamin Bara
2023-04-18T11:10:54Z

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>
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