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    Subject[PATCH tip/core/rcu 09/10] rcu: Fix RCU CPU stall detection in tiny implementation
    Date
    From: Miroslav Benes <mbenes@suse.cz>

    The tiny RCU CPU stall detection depends on *rcp->curtail not being
    NULL. It is however a tail pointer and thus NULL by definition. Instead we
    should check rcp->rcucblist for the presence of pending callbacks which
    need to be processed. With this fix INFO about the stall is printed and
    jiffies_stall (jiffies at next stall) correctly updated.

    Note that the check for pending callback is necessary to avoid spurious
    warnings if there are no pendings callbacks.

    Signed-off-by: Miroslav Benes <mbenes@suse.cz>
    [ paulmck: Fused identical "if" statements, ported to -rcu. ]
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    kernel/rcu/tiny_plugin.h | 7 +++----
    1 file changed, 3 insertions(+), 4 deletions(-)

    diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
    index 858c56569127..80f908afe348 100644
    --- a/kernel/rcu/tiny_plugin.h
    +++ b/kernel/rcu/tiny_plugin.h
    @@ -145,17 +145,16 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
    rcp->ticks_this_gp++;
    j = jiffies;
    js = ACCESS_ONCE(rcp->jiffies_stall);
    - if (*rcp->curtail && ULONG_CMP_GE(j, js)) {
    + if (rcp->rcucblist && ULONG_CMP_GE(j, js)) {
    pr_err("INFO: %s stall on CPU (%lu ticks this GP) idle=%llx (t=%lu jiffies q=%ld)\n",
    rcp->name, rcp->ticks_this_gp, rcu_dynticks_nesting,
    jiffies - rcp->gp_start, rcp->qlen);
    dump_stack();
    - }
    - if (*rcp->curtail && ULONG_CMP_GE(j, js))
    ACCESS_ONCE(rcp->jiffies_stall) = jiffies +
    3 * rcu_jiffies_till_stall_check() + 3;
    - else if (ULONG_CMP_GE(j, js))
    + } else if (ULONG_CMP_GE(j, js)) {
    ACCESS_ONCE(rcp->jiffies_stall) = jiffies + rcu_jiffies_till_stall_check();
    + }
    }

    static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
    --
    1.8.1.5


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