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net: net_enable_timestamp() can be called from irq contexts 

It is now very clear that silly TCP listeners might play with
enabling/disabling timestamping while new children are added
to their accept queue.

Meaning net_enable_timestamp() can be called from BH context
while current state of the static key is not enabled.

Lets play safe and allow all contexts.

The work queue is scheduled only under the problematic cases,
which are the static key enable/disable transition, to not slow down
critical paths.

This extends and improves what we did in commit 5fa8bbda38 ("net: use
a work queue to defer net_disable_timestamp() work")

Fixes: b90e5794c5 ("net: dont call jump_label_dec from irq context")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2017-03-01 14:28:39 -08:00 committed by David S. Miller
parent 540e2894f7
commit 13baa00ad0
1 changed files with 31 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
net/core/dev.c
View File

@ -1698,27 +1698,54 @@ EXPORT_SYMBOL_GPL(net_dec_egress_queue);
static struct static_key netstamp_needed __read_mostly;
#ifdef HAVE_JUMP_LABEL
static atomic_t netstamp_needed_deferred;
static atomic_t netstamp_wanted;
static void netstamp_clear(struct work_struct *work)
{
int deferred = atomic_xchg(&netstamp_needed_deferred, 0);
int wanted;
while (deferred--)
static_key_slow_dec(&netstamp_needed);
wanted = atomic_add_return(deferred, &netstamp_wanted);
if (wanted > 0)
static_key_enable(&netstamp_needed);
else
static_key_disable(&netstamp_needed);
}
static DECLARE_WORK(netstamp_work, netstamp_clear);
#endif
void net_enable_timestamp(void)
{
#ifdef HAVE_JUMP_LABEL
int wanted;
while (1) {
wanted = atomic_read(&netstamp_wanted);
if (wanted <= 0)
break;
if (atomic_cmpxchg(&netstamp_wanted, wanted, wanted + 1) == wanted)
return;
}
atomic_inc(&netstamp_needed_deferred);
schedule_work(&netstamp_work);
#else
static_key_slow_inc(&netstamp_needed);
#endif
}
EXPORT_SYMBOL(net_enable_timestamp);
void net_disable_timestamp(void)
{
#ifdef HAVE_JUMP_LABEL
/* net_disable_timestamp() can be called from non process context */
atomic_inc(&netstamp_needed_deferred);
int wanted;
while (1) {
wanted = atomic_read(&netstamp_wanted);
if (wanted <= 1)
break;
if (atomic_cmpxchg(&netstamp_wanted, wanted, wanted - 1) == wanted)
return;
}
atomic_dec(&netstamp_needed_deferred);
schedule_work(&netstamp_work);
#else
static_key_slow_dec(&netstamp_needed);