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    SubjectRe: 2.6.35->2.6.36 regression, vanilla kernel panic, ppp or hrtimers crashing
    On Wed, Nov 03, 2010 at 10:18:20AM +0200, Denys Fedoryshchenko wrote:
    >
    > On Wednesday 03 November 2010 10:02:58 Jarek Poplawski wrote:
    > > On Wed, Nov 03, 2010 at 09:47:53AM +0200, Denys Fedoryshchenko wrote:
    > > > I try to reverse and got very weird lockups (no netconsole logs and no
    > > > watchdog triggered reboot on that remote machine).
    > > > I will try to cook something to reboot it, because it is very remote
    > > > machine
    > >
    > > OK, I only wanted to know if reverting could be a fast fix. Since it
    > > isn't, please stay with 2.6.35 until there is some new idea (patch).
    > >
    > Well, still i want to try (if i can) more debug, and maybe i'll catch
    > something, also i have around 145 NAS servers to go, to try 2.6.36 :-)

    I think the current debugging needs analyzing first. But here is
    a patch which probably could matter at least wrt your first oopses.
    (Please try this first on something you can easily reboot.)

    Jarek P.
    ---

    diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
    index 09cf56d..1b98c4c 100644
    --- a/drivers/net/ppp_generic.c
    +++ b/drivers/net/ppp_generic.c
    @@ -409,6 +409,8 @@ static ssize_t ppp_read(struct file *file, char __user *buf,

    if (!pf)
    return -ENXIO;
    +
    + atomic_inc(&pf->refcnt);
    add_wait_queue(&pf->rwait, &wait);
    for (;;) {
    set_current_state(TASK_INTERRUPTIBLE);
    @@ -440,6 +442,17 @@ static ssize_t ppp_read(struct file *file, char __user *buf,
    set_current_state(TASK_RUNNING);
    remove_wait_queue(&pf->rwait, &wait);

    + if (atomic_dec_and_test(&pf->refcnt)) {
    + switch (pf->kind) {
    + case INTERFACE:
    + ppp_destroy_interface(PF_TO_PPP(pf));
    + break;
    + case CHANNEL:
    + ppp_destroy_channel(PF_TO_CHANNEL(pf));
    + break;
    + }
    + }
    +
    if (!skb)
    goto out;

    @@ -504,6 +517,8 @@ static unsigned int ppp_poll(struct file *file, poll_table *wait)

    if (!pf)
    return 0;
    +
    + atomic_inc(&pf->refcnt);
    poll_wait(file, &pf->rwait, wait);
    mask = POLLOUT | POLLWRNORM;
    if (skb_peek(&pf->rq))
    @@ -518,6 +533,17 @@ static unsigned int ppp_poll(struct file *file, poll_table *wait)
    mask |= POLLIN | POLLRDNORM;
    }

    + if (atomic_dec_and_test(&pf->refcnt)) {
    + switch (pf->kind) {
    + case INTERFACE:
    + ppp_destroy_interface(PF_TO_PPP(pf));
    + break;
    + case CHANNEL:
    + ppp_destroy_channel(PF_TO_CHANNEL(pf));
    + break;
    + }
    + }
    +
    return mask;
    }


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