lkml.org 
[lkml]   [2012]   [Mar]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    SubjectRe: [PATCH RT] seqlock/rt: Prevent livelocks with seqlocks in RT
    From
    Date
    On Tue, 2012-03-06 at 09:18 +0100, Thomas Gleixner wrote:

    > Errm. rt15 has
    >
    > /*
    > * Starvation safe read side for RT
    > */
    > static inline unsigned read_seqbegin(seqlock_t *sl)
    > {
    > unsigned ret;
    >
    > repeat:
    > ret = sl->seqcount.sequence;
    > if (unlikely(ret & 1)) {
    > /*
    > * Take the lock and let the writer proceed (i.e. evtl
    > * boost it), otherwise we could loop here forever.
    > */
    > spin_lock(&sl->lock);
    > spin_unlock(&sl->lock);
    > goto repeat;
    > }
    > return ret;
    > }
    > #endif

    You're right it does!

    I didn't see this as the lock up showed it was locked up in
    read_seqcount_begin(), it was late and I was tired.

    Here's the real fix then:

    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

    diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
    index 723274d..29ffd4f 100644
    --- a/include/linux/seqlock.h
    +++ b/include/linux/seqlock.h
    @@ -177,7 +177,7 @@ typedef struct {
    /*
    * Read side functions for starting and finalizing a read side section.
    */
    -#ifndef CONFIG_PREEMPT_RT
    +#ifndef CONFIG_PREEMPT_RT_FULL
    static inline unsigned read_seqbegin(const seqlock_t *sl)
    {
    return read_seqcount_begin(&sl->seqcount);



    \
     
     \ /
      Last update: 2012-03-06 13:19    [W:0.021 / U:59.344 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site