On Thu, Apr 13, 2023 at 09:46:40AM +0200, Benjamin Bara wrote:
> From: Benjamin Bara <benjamin.bara@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx # v5.2+
> Suggested-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> Signed-off-by: Benjamin Bara <benjamin.bara@xxxxxxxxxxx>
So, with Peter's input and me checking again:
Acked-by: Wolfram Sang <wsa@xxxxxxxxxx>
I assume this shall go in via the mfd-tree. Let me know if I should pick
it instead.
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