• Thomas Gleixner's avatar
    timekeeping: Split jiffies seqlock · e5d4d175
    Thomas Gleixner authored
    seqlock consists of a sequence counter and a spinlock_t which is used to
    serialize the writers. spinlock_t is substituted by a "sleeping" spinlock
    on PREEMPT_RT enabled kernels which breaks the usage in the timekeeping
    code as the writers are executed in hard interrupt and therefore
    non-preemptible context even on PREEMPT_RT.
    
    The spinlock in seqlock cannot be unconditionally replaced by a
    raw_spinlock_t as many seqlock users have nesting spinlock sections or
    other code which is not suitable to run in truly atomic context on RT.
    
    Instead of providing a raw_seqlock API for a single use case, open code the
    seqlock for the jiffies use case and implement it with a raw_spinlock_t and
    a sequence counter.
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20200321113242.120587764@linutronix.de
    e5d4d175
tick-common.c 14.6 KB