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    Subject[PATCH 3.12 75/77] sched: Fix cfs_bandwidth misuse of hrtimer_expires_remaining
    Date
    3.12-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Ben Segall <bsegall@google.com>

    commit db06e78cc13d70f10877e0557becc88ab3ad2be8 upstream.

    hrtimer_expires_remaining does not take internal hrtimer locks and thus
    must be guarded against concurrent __hrtimer_start_range_ns (but
    returning HRTIMER_RESTART is safe). Use cfs_b->lock to make it safe.

    Signed-off-by: Ben Segall <bsegall@google.com>
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Cc: pjt@google.com
    Link: http://lkml.kernel.org/r/20131016181617.22647.73829.stgit@sword-of-the-dawn.mtv.corp.google.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Cc: Chris J Arges <chris.j.arges@canonical.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/sched/fair.c | 14 +++++++++++---
    1 file changed, 11 insertions(+), 3 deletions(-)

    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -2519,7 +2519,13 @@ static const u64 min_bandwidth_expiratio
    /* how long we wait to gather additional slack before distributing */
    static const u64 cfs_bandwidth_slack_period = 5 * NSEC_PER_MSEC;

    -/* are we near the end of the current quota period? */
    +/*
    + * Are we near the end of the current quota period?
    + *
    + * Requires cfs_b->lock for hrtimer_expires_remaining to be safe against the
    + * hrtimer base being cleared by __hrtimer_start_range_ns. In the case of
    + * migrate_hrtimers, base is never cleared, so we are fine.
    + */
    static int runtime_refresh_within(struct cfs_bandwidth *cfs_b, u64 min_expire)
    {
    struct hrtimer *refresh_timer = &cfs_b->period_timer;
    @@ -2595,10 +2601,12 @@ static void do_sched_cfs_slack_timer(str
    u64 expires;

    /* confirm we're still not at a refresh boundary */
    - if (runtime_refresh_within(cfs_b, min_bandwidth_expiration))
    + raw_spin_lock(&cfs_b->lock);
    + if (runtime_refresh_within(cfs_b, min_bandwidth_expiration)) {
    + raw_spin_unlock(&cfs_b->lock);
    return;
    + }

    - raw_spin_lock(&cfs_b->lock);
    if (cfs_b->quota != RUNTIME_INF && cfs_b->runtime > slice) {
    runtime = cfs_b->runtime;
    cfs_b->runtime = 0;



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