On Sun, 10 Aug 2008, sven.wegener@xxxxxxxxxxx wrote:
> From: Sven Wegener <sven.wegener@xxxxxxxxxxx>
>
> There is a slight chance for a deadlock in the estimator code. We can't call
> del_timer_sync() while holding our lock, as the timer might be active and
> spinning for the lock on another cpu. Work around this issue by using
> try_to_del_timer_sync() and releasing the lock. We could actually delete the
> timer outside of our lock, as the add and kill functions are only every called
> from userspace via [gs]etsockopt() and are serialized by a mutex, but better
> make this explicit.
>
> Signed-off-by: Sven Wegener <sven.wegener@xxxxxxxxxxx>
> Cc: stable <stable@xxxxxxxxxx>
> ---
> net/ipv4/ipvs/ip_vs_est.c | 7 +++++--
> 1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/ipvs/ip_vs_est.c b/net/ipv4/ipvs/ip_vs_est.c
> index bc04eed..1d6e58e 100644
> --- a/net/ipv4/ipvs/ip_vs_est.c
> +++ b/net/ipv4/ipvs/ip_vs_est.c
> @@ -170,8 +170,11 @@ void ip_vs_kill_estimator(struct ip_vs_stats *stats)
> kfree(est);
> killed++;
> }
> - if (killed && est_list == NULL)
> - del_timer_sync(&est_timer);
> + while (killed && !est_list && try_to_del_timer_sync(&est_timer) < 0) {
> + write_unlock_bh(&est_lock);
> + cpu_relax();
> + write_lock_bh(&est_lock);
> + }
> write_unlock_bh(&est_lock);
> }
>
As a side note, just noticed that this opens another race condition, if we
leave the mutex serializing the [gs]etsockopt calls out:
If the timer reschedules itself, after we just removed the last estimator,
but we failed to deactivate the timer due to it being active, we have the
chance of add_timer() on already pending timer during creating a new
estimator. This will then trigger the BUG_ON() in add_timer(). Thanks to
the mutex this can't happen currently.
The "ipvs: Embed estimator object into stats object" patch will move to
code from add_timer() to mod_timer() so at the the end of this series
we're safe.
Sven
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