Re: net: suspicious RCU usage in nf_hook
From: Eric Dumazet <hidden>
Date: 2017-02-01 21:16:16
Also in:
lkml, netfilter-devel
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
On Wed, 2017-02-01 at 12:51 -0800, Cong Wang wrote:
quoted hunk ↗ jump to hunk
On Tue, Jan 31, 2017 at 7:44 AM, Eric Dumazet [off-list ref] wrote:quoted
On Mon, 2017-01-30 at 22:19 -0800, Cong Wang wrote:quoted
The context is process context (TX path before hitting qdisc), and BH is not disabled, so in_interrupt() doesn't catch it. Hmm, this makes me thinking maybe we really need to disable BH in this case for nf_hook()? But it is called in RX path too, and BH is already disabled there.ipt_do_table() and similar netfilter entry points disable BH. Maybe it is done too late.I think we need a fix like the following one for minimum impact.diff --git a/net/core/dev.c b/net/core/dev.c index 727b6fd..eee7d63 100644 --- a/net/core/dev.c +++ b/net/core/dev.c@@ -1720,12 +1720,10 @@ EXPORT_SYMBOL(net_enable_timestamp); void net_disable_timestamp(void) { #ifdef HAVE_JUMP_LABEL - if (in_interrupt()) { - atomic_inc(&netstamp_needed_deferred); - return; - } -#endif + atomic_inc(&netstamp_needed_deferred); +#else static_key_slow_dec(&netstamp_needed); +#endif } EXPORT_SYMBOL(net_disable_timestamp);
This would permanently leave the kernel in the netstamp_needed state. I would prefer the patch using a process context to perform the cleanup ? Note there is a race window, but probably not a big deal. net/core/dev.c | 30 ++++++++++-------------------- 1 file changed, 10 insertions(+), 20 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index 7f218e095361520d11c243d650e053321ea7274f..1cae681b6cfd1cf2c9bee7072eb8af9cf79cced8 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c@@ -1695,37 +1695,27 @@ EXPORT_SYMBOL_GPL(net_dec_egress_queue); static struct static_key netstamp_needed __read_mostly; #ifdef HAVE_JUMP_LABEL -/* We are not allowed to call static_key_slow_dec() from irq context - * If net_disable_timestamp() is called from irq context, defer the - * static_key_slow_dec() calls. - */ static atomic_t netstamp_needed_deferred; -#endif - -void net_enable_timestamp(void) +static void netstamp_clear(struct work_struct *work) { -#ifdef HAVE_JUMP_LABEL int deferred = atomic_xchg(&netstamp_needed_deferred, 0); - if (deferred) { - while (--deferred) - static_key_slow_dec(&netstamp_needed); - return; - } + while (deferred--) + static_key_slow_dec(&netstamp_needed); +} +static DECLARE_WORK(netstamp_work, netstamp_clear); #endif + +void net_enable_timestamp(void) +{ static_key_slow_inc(&netstamp_needed); } EXPORT_SYMBOL(net_enable_timestamp); void net_disable_timestamp(void) { -#ifdef HAVE_JUMP_LABEL - if (in_interrupt()) { - atomic_inc(&netstamp_needed_deferred); - return; - } -#endif - static_key_slow_dec(&netstamp_needed); + atomic_inc(&netstamp_needed_deferred); + schedule_work(&netstamp_work); } EXPORT_SYMBOL(net_disable_timestamp);