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    Subject[PATCH AUTOSEL 5.16 18/52] sched: Avoid double preemption in __cond_resched_*lock*()
    Date
    From: Peter Zijlstra <peterz@infradead.org>

    [ Upstream commit 7e406d1ff39b8ee574036418a5043c86723170cf ]

    For PREEMPT/DYNAMIC_PREEMPT the *_unlock() will already trigger a
    preemption, no point in then calling preempt_schedule_common()
    *again*.

    Use _cond_resched() instead, since this is a NOP for the preemptible
    configs while it provide a preemption point for the others.

    Reported-by: xuhaifeng <xuhaifeng@oppo.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/YcGnvDEYBwOiV0cR@hirez.programming.kicks-ass.net
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/sched/core.c | 12 +++---------
    1 file changed, 3 insertions(+), 9 deletions(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 77563109c0ea0..d24823b3c3f9f 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -8176,9 +8176,7 @@ int __cond_resched_lock(spinlock_t *lock)

    if (spin_needbreak(lock) || resched) {
    spin_unlock(lock);
    - if (resched)
    - preempt_schedule_common();
    - else
    + if (!_cond_resched())
    cpu_relax();
    ret = 1;
    spin_lock(lock);
    @@ -8196,9 +8194,7 @@ int __cond_resched_rwlock_read(rwlock_t *lock)

    if (rwlock_needbreak(lock) || resched) {
    read_unlock(lock);
    - if (resched)
    - preempt_schedule_common();
    - else
    + if (!_cond_resched())
    cpu_relax();
    ret = 1;
    read_lock(lock);
    @@ -8216,9 +8212,7 @@ int __cond_resched_rwlock_write(rwlock_t *lock)

    if (rwlock_needbreak(lock) || resched) {
    write_unlock(lock);
    - if (resched)
    - preempt_schedule_common();
    - else
    + if (!_cond_resched())
    cpu_relax();
    ret = 1;
    write_lock(lock);
    --
    2.34.1
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