• Paul E. McKenney's avatar
    rcu: Improve diagnostics for spurious RCU CPU stall warnings · 6ccd2ecd
    Paul E. McKenney authored
    
    
    The current RCU CPU stall warning code will print "Stall ended before
    state dump start" any time that the stall-warning code is triggered on
    a CPU that has already reported a quiescent state for the current grace
    period and if all quiescent states have been reported for the current
    grace period.  However, a true stall can result in these symptoms, for
    example, by preventing RCU's grace-period kthreads from ever running
    
    This commit therefore checks for this condition, reporting the end of
    the stall only if one of the grace-period counters has actually advanced.
    Otherwise, it reports the last time that the grace-period kthread made
    meaningful progress.  (In normal situations, the grace-period kthread
    should make meaningful progress at least every jiffies_till_next_fqs
    jiffies.)
    
    Reported-by: default avatarMiroslav Benes <mbenes@suse.cz>
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Tested-by: default avatarMiroslav Benes <mbenes@suse.cz>
    6ccd2ecd