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rcu-tasks: Remove open-coded one-byte cmpxchg() emulation

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This commit removes the open-coded one-byte cmpxchg() emulation from
rcu_trc_cmpxchg_need_qs(), replacing it with just cmpxchg() given the
latter's new-found ability to handle single-byte arguments across all
architectures.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit is contained in:
Paul E. McKenney 2024-10-09 11:00:45 -07:00 committed by Frederic Weisbecker
parent 0a116dc86d
commit d4e287d7ca
1 changed files with 1 additions and 16 deletions
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17
kernel/rcu/tasks.h
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@ -1541,22 +1541,7 @@ static void rcu_st_need_qs(struct task_struct *t, u8 v)
*/
u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new)
{
union rcu_special ret;
union rcu_special trs_old = READ_ONCE(t->trc_reader_special);
union rcu_special trs_new = trs_old;
if (trs_old.b.need_qs != old)
return trs_old.b.need_qs;
trs_new.b.need_qs = new;
// Although cmpxchg() appears to KCSAN to update all four bytes,
// only the .b.need_qs byte actually changes.
instrument_atomic_read_write(&t->trc_reader_special.b.need_qs,
sizeof(t->trc_reader_special.b.need_qs));
// Avoid false-positive KCSAN failures.
ret.s = data_race(cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s));
return ret.b.need_qs;
return cmpxchg(&t->trc_reader_special.b.need_qs, old, new);
}
EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs);