Messages in this thread Patch in this message | | | Date | Wed, 25 Oct 2023 08:43:51 +0800 | From | Rong Tao <> | Subject | [PATCH] stop_machine: pass curstate to ack_state() |
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The multi_cpu_stop() state machine uses multi_stop_data::state to hold the current state, and this is read and written atomically except in ack_state(), which performs a non-atomic read.
As ack_state() only performs this non-atomic read when there is a single writer, this is benign, but it makes reasoning about the state machine a little harder.
Remove the non-atomic read and pass the (atomically read) curstate in instead. This makes it clear that we do not expect any racy writes, and avoids a redundant load.
Acked-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Rong Tao <rongtao@cestc.cn> --- kernel/stop_machine.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index cedb17ba158a..268c2e581698 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -188,10 +188,11 @@ static void set_state(struct multi_stop_data *msdata, }
/* Last one to ack a state moves to the next state. */ -static void ack_state(struct multi_stop_data *msdata) +static void ack_state(struct multi_stop_data *msdata, + enum multi_stop_state curstate) { if (atomic_dec_and_test(&msdata->thread_ack)) - set_state(msdata, msdata->state + 1); + set_state(msdata, curstate + 1); }
notrace void __weak stop_machine_yield(const struct cpumask *cpumask) @@ -242,7 +243,7 @@ static int multi_cpu_stop(void *data) default: break; } - ack_state(msdata); + ack_state(msdata, curstate); } else if (curstate > MULTI_STOP_PREPARE) { /* * At this stage all other CPUs we depend on must spin -- 2.42.0
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