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    Subject[PATCH 5.10 16/83] xen/balloon: fix cancelled balloon action
    Date
    From: Juergen Gross <jgross@suse.com>

    commit 319933a80fd4f07122466a77f93e5019d71be74c upstream.

    In case a ballooning action is cancelled the new kernel thread handling
    the ballooning might end up in a busy loop.

    Fix that by handling the cancelled action gracefully.

    While at it introduce a short wait for the BP_WAIT case.

    Cc: stable@vger.kernel.org
    Fixes: 8480ed9c2bbd56 ("xen/balloon: use a kernel thread instead a workqueue")
    Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
    Signed-off-by: Juergen Gross <jgross@suse.com>
    Tested-by: Jason Andryuk <jandryuk@gmail.com>
    Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Link: https://lore.kernel.org/r/20211005133433.32008-1-jgross@suse.com
    Signed-off-by: Juergen Gross <jgross@suse.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/xen/balloon.c | 21 +++++++++++++++------
    1 file changed, 15 insertions(+), 6 deletions(-)

    --- a/drivers/xen/balloon.c
    +++ b/drivers/xen/balloon.c
    @@ -491,12 +491,12 @@ static enum bp_state decrease_reservatio
    }

    /*
    - * Stop waiting if either state is not BP_EAGAIN and ballooning action is
    - * needed, or if the credit has changed while state is BP_EAGAIN.
    + * Stop waiting if either state is BP_DONE and ballooning action is
    + * needed, or if the credit has changed while state is not BP_DONE.
    */
    static bool balloon_thread_cond(enum bp_state state, long credit)
    {
    - if (state != BP_EAGAIN)
    + if (state == BP_DONE)
    credit = 0;

    return current_credit() != credit || kthread_should_stop();
    @@ -516,10 +516,19 @@ static int balloon_thread(void *unused)

    set_freezable();
    for (;;) {
    - if (state == BP_EAGAIN)
    - timeout = balloon_stats.schedule_delay * HZ;
    - else
    + switch (state) {
    + case BP_DONE:
    + case BP_ECANCELED:
    timeout = 3600 * HZ;
    + break;
    + case BP_EAGAIN:
    + timeout = balloon_stats.schedule_delay * HZ;
    + break;
    + case BP_WAIT:
    + timeout = HZ;
    + break;
    + }
    +
    credit = current_credit();

    wait_event_freezable_timeout(balloon_thread_wq,

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